AC won't take freon

[flintknapper]

Ok I did a search Foo, to get my new system chillin, so I pulled a consistent vacuum , using gauges and I trying to charge the system but my friend said the compressor must engage, and I think the system needs freon in it to get the clutch to engage, he told me, to jumper the Pressure switch by the battery and I get nothing. @flintknapper I see you are very knowledgeable on the AC system because I am not . I am using a new compressor and this is on my Cummins swapped 80

Send your friend on an errand and while he is gone, charge your system.

Don't bother jumping the pressure switch (assuming it works OK now).

You are right, the system needs to have a minimum amount of pressure (usually about 30 psi) in order to satisfy the low pressure side of the binary switch (Pressure Switch). Your binary switch will not allow the compressor clutch to kick in if the pressure is too low or too high.

So how do we get refrigerant into the system if the compressor won't run?

We pull a vacuum on the system and let the vacuum suck the first 8-12ozs into the system.

Rather than walk you through the entire process I am just going to paste instructions that I made for another forum member here a couple of Summers ago. You can read through it and follow it verbatim or pick up at whatever point you are at now.

This addresses adding refrigerant to a system that has been evacuated (no Freon in the system). It assumes you have already added oil.

BE SURE you understand the procedure for charging the first can (as a liquid) into vacuum through the high side (ENGINE OFF). If you have any questions about it....ask here first.

A/C Pump Down and Recharge

​

• Before final pump down the system should be checked for leaks by first pulling a vacuum on the system for 15-20 minutes. Shut off manifold valves BEFORE turning off vacuum pump. If after 45 minutes there is no significant vacuum loss, you may assume there are no leaks and it is safe to proceed with pumping down the system in preparation for the recharge.
• It is important to pull a ‘deep’ vacuum on the system before recharging. This means a minimum of 1-1/2 to 2 hours. Your gauge will quickly pull into a negative reading (vacuum) BUT it takes time for any moisture to boil off and be removed from the system, so don’t rush this.
• Once you have waited the proper amount of time, turn off your low and high side valves while the vacuum pump is still running. This will help prevent the possibility of air getting back into the system (provided your lines and connections are good).
• Leave your high and low side lines hooked up to the A/C ports but remove the Yellow (center) line from your vacuum pump and connect your first can of refrigerant to it. Each and every time you connect a new can to the center line, you will need to ‘purge’ that line. We don’t want air/moisture going back into the system. So once the can is hooked up and pierced…crack the connection at the manifold just enough to let a small mist of refrigerant escape…then hand tighten it back. IF your manifold has a Schrader valve at the location, just depress it. That is what it is there for (purging the line).
• Now you are ready to introduce the first can of refrigerant as a liquid into the system. We are going to do this (FIRST CAN ONLY) through the high side. Since the system is under vacuum it will quite readily suck a good amount of refrigerant into the system just as it is (ENGINE OFF, COMPRESSOR OFF). Never open the high side line with the engine running and the compressor on.
• To charge into vacuum through the high side: Turn your refrigerant can upside down (point the end you have tapped toward the ground) so that ‘liquid’ refrigerant will enter the system when we open the high side valve. With the can inverted, open the high side (and ONLY the high side valve) all the way. The refrigerant will be sucked into the system within a couple of minutes (usually less). You will feel the can getting noticeably lighter and colder. Once you are confident the can has emptied, close the high side valve. We will NOT open the high side valve again during the remaining charging sequences.
• You now want to hand turn the compressor 8-10 full revolutions (belt should not be on yet or just loosely fitted). This will pump a small amount of refrigerant and oil through the system before we start it up. Then connect the belt and tighten it.
• The remaining refrigerant charge will be done through the low side, with the engine running, compressor on, A/C set to high and windows open.
• As before, connect a new can of refrigerant to the yellow center line of your gauge set and ‘purge’ the line. The refrigerant can MUST now be held upright so that only ‘gas’ enters the suction side of the compressor. We don’t want any liquid refrigerant going into the low side…since it is ‘possible’ to slug your compressor. There are a few exceptions to this warning…that I will cover later, but at this stage, the rule is: Only refrigerant in its gaseous state is to enter the compressors low side.
• Slowly open the low side valve (NOT ALL THE WAY) watch for the low side pressure to build…but not exceed 60-75lbs. Use the low side valve to control this. As the refrigerant is taken into the system (it takes a while, especially if it isn’t hot outside) you will be able to open the valve nearly all the way.
• After your second can has emptied (typical 12oz cans) you should have 24 ounces in the system. We want to shoot for 30-31 ounces total (can be adjusted later) so you will be using a part (roughly ½) of the third can. Expect the last bit of this charge to go in more slowly, be patient. This is also the time that we need to start paying attention to our gauge pressures and vent temperatures.
• Since we are basically ‘weighing in’ the refrigerant amount, we are in no fear of overcharging the system, but we want to find the point at which increasing system pressure no longer results in lower vent temps (diminishing returns).
• This is the point where I would like to be in communication with you. You may have questions…or I may need to ask you some.

General information:

*Make sure all valves are turned OFF before disconnecting or changing out refrigerant cans, we don’t want to lose any refrigerant charge or get air into the system.

*Pressure readings (for high and low side comparison) are taken with the Valves Closed. Some folks like to increase engine speed to 1200-1500 rpm to simulate high idle or just off idle speed, but there is no real advantage to this IMO. Just let the system stabilize (run at idle for 10 minutes) and note your pressures.

*Pressure readings will vary with the ambient (outside) temperature. So we will need to know the ambient temperature (or a good guess) in order for our pressures to mean anything.

*Each system…depending upon component condition and outside influences (heat loads from the environment) will work best at a specific charge level (a little less or more than the factor y spec). This is where the knowledgeable owner can take the time to ‘fine tune’ his system by adding or removing small amounts of refrigerant until you find the ‘sweet spot’ for your system.

*Your system (everyone’s system) will work better at highway speeds than at slower speeds or in stop and go traffic. Any time the compressor is turning faster and you have more air flow across the condenser (more heat exchange) the better the system will cool, so just expect that.

*If you can get vent temps that are 30-35° F below that of the ambient temp..then your system is working very well. You might get more than that…but the 80 series is hard to cool.

*Since you have taken the time to learn about you’re A/C system and equip yourself to work on it, you can now check it from time to time to see what your pressures are, trouble shoot it and work on it if needed.

***Lastly…I warned you never to let liquid refrigerant enter the low side of the compressor. In reality…you might have trouble getting the last few ounces of refrigerant into the system (especially in cooler weather). So it is permissible to quickly tilt the can on its side and then immediately back upright to let a LITTLE liquid into the system. The chances of slugging the compressor like this are exceedingly small. You will see the low side pressure jump/spike for just a second when you do this but generally it will not harm anything. Alternately, you can take a hair dryer and warm the can to force the last bit of charge into the system.

 

[shocktower]

Send your friend on an errand and while he is gone, charge your system.

Don't bother jumping the pressure switch (assuming it works OK now).

You are right, the system needs to have a minimum amount of pressure (usually about 30 psi) in order to satisfy the low pressure side of the binary switch (Pressure Switch). Your binary switch will not allow the compressor clutch to kick in if the pressure is too low or too high.

So how do we get refrigerant into the system if the compressor won't run?

We pull a vacuum on the system and let the vacuum suck the first 8-12ozs into the system.

Rather than walk you through the entire process I am just going to paste instructions that I made for another forum member here a couple of Summers ago. You can read through it and follow it verbatim or pick up at whatever point you are at now.

This addresses adding refrigerant to a system that has been evacuated (no Freon in the system). It assumes you have already added oil.

BE SURE you understand the procedure for charging the first can (as a liquid) into vacuum through the high side (ENGINE OFF). If you have any questions about it....ask here first.

A/C Pump Down and Recharge

​

• Before final pump down the system should be checked for leaks by first pulling a vacuum on the system for 15-20 minutes. Shut off manifold valves BEFORE turning off vacuum pump. If after 45 minutes there is no significant vacuum loss, you may assume there are no leaks and it is safe to proceed with pumping down the system in preparation for the recharge.
• It is important to pull a ‘deep’ vacuum on the system before recharging. This means a minimum of 1-1/2 to 2 hours. Your gauge will quickly pull into a negative reading (vacuum) BUT it takes time for any moisture to boil off and be removed from the system, so don’t rush this.
• Once you have waited the proper amount of time, turn off your low and high side valves while the vacuum pump is still running. This will help prevent the possibility of air getting back into the system (provided your lines and connections are good).
• Leave your high and low side lines hooked up to the A/C ports but remove the Yellow (center) line from your vacuum pump and connect your first can of refrigerant to it. Each and every time you connect a new can to the center line, you will need to ‘purge’ that line. We don’t want air/moisture going back into the system. So once the can is hooked up and pierced…crack the connection at the manifold just enough to let a small mist of refrigerant escape…then hand tighten it back. IF your manifold has a Schrader valve at the location, just depress it. That is what it is there for (purging the line).
• Now you are ready to introduce the first can of refrigerant as a liquid into the system. We are going to do this (FIRST CAN ONLY) through the high side. Since the system is under vacuum it will quite readily suck a good amount of refrigerant into the system just as it is (ENGINE OFF, COMPRESSOR OFF). Never open the high side line with the engine running and the compressor on.
• To charge into vacuum through the high side: Turn your refrigerant can upside down (point the end you have tapped toward the ground) so that ‘liquid’ refrigerant will enter the system when we open the high side valve. With the can inverted, open the high side (and ONLY the high side valve) all the way. The refrigerant will be sucked into the system within a couple of minutes (usually less). You will feel the can getting noticeably lighter and colder. Once you are confident the can has emptied, close the high side valve. We will NOT open the high side valve again during the remaining charging sequences.
• You now want to hand turn the compressor 8-10 full revolutions (belt should not be on yet or just loosely fitted). This will pump a small amount of refrigerant and oil through the system before we start it up. Then connect the belt and tighten it.
• The remaining refrigerant charge will be done through the low side, with the engine running, compressor on, A/C set to high and windows open.
• As before, connect a new can of refrigerant to the yellow center line of your gauge set and ‘purge’ the line. The refrigerant can MUST now be held upright so that only ‘gas’ enters the suction side of the compressor. We don’t want any liquid refrigerant going into the low side…since it is ‘possible’ to slug your compressor. There are a few exceptions to this warning…that I will cover later, but at this stage, the rule is: Only refrigerant in its gaseous state is to enter the compressors low side.
• Slowly open the low side valve (NOT ALL THE WAY) watch for the low side pressure to build…but not exceed 60-75lbs. Use the low side valve to control this. As the refrigerant is taken into the system (it takes a while, especially if it isn’t hot outside) you will be able to open the valve nearly all the way.
• After your second can has emptied (typical 12oz cans) you should have 24 ounces in the system. We want to shoot for 30-31 ounces total (can be adjusted later) so you will be using a part (roughly ½) of the third can. Expect the last bit of this charge to go in more slowly, be patient. This is also the time that we need to start paying attention to our gauge pressures and vent temperatures.
• Since we are basically ‘weighing in’ the refrigerant amount, we are in no fear of overcharging the system, but we want to find the point at which increasing system pressure no longer results in lower vent temps (diminishing returns).
• This is the point where I would like to be in communication with you. You may have questions…or I may need to ask you some.

General information:

*Make sure all valves are turned OFF before disconnecting or changing out refrigerant cans, we don’t want to lose any refrigerant charge or get air into the system.

*Pressure readings (for high and low side comparison) are taken with the Valves Closed. Some folks like to increase engine speed to 1200-1500 rpm to simulate high idle or just off idle speed, but there is no real advantage to this IMO. Just let the system stabilize (run at idle for 10 minutes) and note your pressures.

*Pressure readings will vary with the ambient (outside) temperature. So we will need to know the ambient temperature (or a good guess) in order for our pressures to mean anything.

*Each system…depending upon component condition and outside influences (heat loads from the environment) will work best at a specific charge level (a little less or more than the factor y spec). This is where the knowledgeable owner can take the time to ‘fine tune’ his system by adding or removing small amounts of refrigerant until you find the ‘sweet spot’ for your system.

*Your system (everyone’s system) will work better at highway speeds than at slower speeds or in stop and go traffic. Any time the compressor is turning faster and you have more air flow across the condenser (more heat exchange) the better the system will cool, so just expect that.

*If you can get vent temps that are 30-35° F below that of the ambient temp..then your system is working very well. You might get more than that…but the 80 series is hard to cool.

*Since you have taken the time to learn about you’re A/C system and equip yourself to work on it, you can now check it from time to time to see what your pressures are, trouble shoot it and work on it if needed.

***Lastly…I warned you never to let liquid refrigerant enter the low side of the compressor. In reality…you might have trouble getting the last few ounces of refrigerant into the system (especially in cooler weather). So it is permissible to quickly tilt the can on its side and then immediately back upright to let a LITTLE liquid into the system. The chances of slugging the compressor like this are exceedingly small. You will see the low side pressure jump/spike for just a second when you do this but generally it will not harm anything. Alternately, you can take a hair dryer and warm the can to force the last bit of charge into the system.

Ok I think I got it, but I am using a big green can of the 134 sitting on a scale to weigh it out from the bulk cylinder do I need to do anything special ??

 

[flintknapper]

Ok I think I got it, but I am using a big green can of the 134 sitting on a scale to weigh it out from the bulk cylinder do I need to do anything special ??

No, just weigh it in. (Check weight of cylinder after a minute or so). You'll still need to invert the cylinder to get liquid refrigerant. The high and low side will probably equalize before you could put too much refrigerant in (by vacuum). We just want to get enough in to satisfy the low pressure requirement and also have liquid refrigerant available immediately to carry the oil though the system. You'll finish your charge though the low side (gaseous refrigerant). Do you have a small vent temperature gauge/thermometer?

 

[shocktower]

No, just weigh it in. (Check weight of cylinder after a minute or so). You'll still need to invert the cylinder to get liquid refrigerant. The high and low side will probably equalize before you could put too much refrigerant in (by vacuum). We just want to get enough in to satisfy the low pressure requirement and also have liquid refrigerant available immediately to carry the oil though the system. You'll finish your charge though the low side (gaseous refrigerant). Do you have a small vent temperature gauge/thermometer?

View attachment 2653267

Ok I will do this and I will get a vent temp gauge . Thank you so much I feel like Neo in the matrix

 

[flintknapper]

Ok I will do this and I will get a vent temp gauge . Thank you so much I feel like Neo in the matrix

IF you have problems or just have questions, don't hesitate to ask. We are happy to help. There are several well qualified persons aboard who can guide you. I will do all I can as well.

A/C work can seem daunting at first....but if done right (follow the instructions, don't take short cuts) it can be done by almost anyone.

We just don't want to have to do it all twice.

 

[GeoRoss]

@flintknapper I think is referring to me. He was invaluable helping me completely redo my system. Flushed all the lines, new o-rings and schrader valves, condenser, compressor, drier, expansion valve. The only thing I didn't replace was the evaporator. If it is under 105˚ it blows below 50˚. Someday I may add an e-fan for when driving in traffic on those really hot days, but since the cruiser has retired from being a daily I probably won't.

 

[flintknapper]

@flintknapper I think is referring to me. He was invaluable helping me completely redo my system. Flushed all the lines, new o-rings and schrader valves, condenser, compressor, drier, expansion valve. The only thing I didn't replace was the evaporator. If it is under 105˚ it blows below 50˚. Someday I may add an e-fan for when driving in traffic on those really hot days, but since the cruiser has retired from being a daily I probably won't.

You were a champ Sir. Did a great job!

 

[re_guderian]

Bumping an old thread, and not for an 80, but for my (POS) Hyundai... I can't get the small cans to vapor charge on the low side after pulling a vacuum for a long time. I've purged lines, followed all the instructions. It's also like 110 degrees outside, could that be the problem? It took over 20 minutes for 4 oz of the the second 12 oz can into a system designed for 22-24 ozs. Is it just too hot ambient to charge? What is a typical can pressure? At these (110) ambients, my low side reading is near 40, and the high side near 300 with only 16 oz in the system. From what I gather from the temp/pressure charts, that's not TOO bad? System held vacuum no problem. Getting "coolish" air out the vents with only that much in the system, but would really like to add the full charge by weight. Thoughts from those with more experience than me?

 

[flintknapper]

Bumping an old thread, and not for an 80, but for my (POS) Hyundai... I can't get the small cans to vapor charge on the low side after pulling a vacuum for a long time. I've purged lines, followed all the instructions. It's also like 110 degrees outside, could that be the problem? It took over 20 minutes for 4 oz of the the second 12 oz can into a system designed for 22-24 ozs. Is it just too hot ambient to charge? What is a typical can pressure? At these (110) ambients, my low side reading is near 40, and the high side near 300 with only 16 oz in the system. From what I gather from the temp/pressure charts, that's not TOO bad? System held vacuum no problem. Getting "coolish" air out the vents with only that much in the system, but would really like to add the full charge by weight. Thoughts from those with more experience than me?

Yes, you definitely want to have the full 'weighted' charge in the system. What you are experiencing is not unusual when performing a new recharge and doing so from the low side only (vapor charge, engine running). The last few ounces can be difficult to get into the system. The ambient temperature is not an issue for you....in fact working in your favor with respect to can pressure.

Your Low and High side pressures (for the ambient of 110°F) are about what I would expect to see at the system charge level you have presently. Once you get the remainder of the refrigerant in (at the same ambient) I would not be surprised to see your low side go up to around 50 psi and high side as high as 335°F or better.

Since it doesn't appear you have any restrictions....I would be inclined to 'force feed' the last few ounces. What I mean by that is 'forcing' the compressor to accept SMALL amounts of 'liquid' refrigerant. Generally we do NOT want the compressor to see anything but 'gas' since liquids are not compressible. But in reality (under some conditions) they do see small amounts of liquid refrigerant from the evaporator anyway.

It is vitally important not to SLUG the compressor however. That said....the way to force feed the last few ounces is as follows:

1. Engine running, compressor on, AC set on high, fan on high, windows down.

2. Let engine and compressor run until the engine has reached normal operating temperature and the high and low side pressures have stabilized. Both Valves (high and low side) will be off at this point.

3. Hook up your can to the middle hose of your manifold gauge set and 'purge' that line a small amount.

4. Now fully open your middle service line valve. Depending on your manifold set it may have a valve on the manifold or you may only have a valve at the can tap/adapter. In any case...fully open that circuit.

5. Next (with can facing up/can tap accepting gas only) open your low side valve fully. Let low side gauge settle for a minute or so.

6. Now we begin the 'force feed'. Take the refrigerant can in hand and with quick, short rotations of the wrist....tilt it over about 90° so that a SMALL amount of liquid refrigerant gets sucked up. IF your manifold has a 'sight window' you will see a small amount of liquid refrigerant appear. As soon as you see liquid.... tilt the can back up vertically and wait for it to disappear.

You will see a sharp spike on the low side pressure gauge each time this happens. This is evidence the refrigerant reached the compressor. Continue to do this SLOWLY (it can take 15-minutes) to get 4-6 ounces in. Once you feel you have charged in the proper weight, turn off all valves let the unit run, check your pressures (now stabilized) and take a vent temp reading.

NOTES:

With very high ambient temps and in environments with high Solar Gain (Sun Belt States) a system achieving vent temps 30-35°F below the ambient is doing about it can do. And you should be quite happy with that. IF it does better than that (highway speeds, overcast, etc) great....but don't expect it.

Tip: When hooking up your manifold gauge hoses (to manifold and adapter) do NOT over-tighten. Just tighten snugly by hand. We don't want leaks obviously, but I see many people crushing the seals in either end. This eventually deforms the seal and it will block (partially or wholly) the line. You can almost expect this with rented equipment.

Disclaimer: Perform a 'force feed' at your own risk. I am not there to show you. Do so slowly and don't slug your compressor. Or if in doubt take it to a professional. It is an easily performed technique, done daily at shops and in driveways all over....but some folks can break an anvil with a rubber hammer. Just saying............

 

[re_guderian]

Yes, you definitely want to have the full 'weighted' charge in the system. What you are experiencing is not unusual when performing a new recharge and doing so from the low side only (vapor charge, engine running). The last few ounces can be difficult to get into the system. The ambient temperature is not an issue for you....in fact working in your favor with respect to can pressure.

Your Low and High side pressures (for the ambient of 110°F) are about what I would expect to see at the system charge level you have presently. Once you get the remainder of the refrigerant in (at the same ambient) I would not be surprised to see your low side go up to around 50 psi and high side as high as 335°F or better.

Since it doesn't appear you have any restrictions....I would be inclined to 'force feed' the last few ounces. What I mean by that is 'forcing' the compressor to accept SMALL amounts of 'liquid' refrigerant. Generally we do NOT want the compressor to see anything but 'gas' since liquids are not compressible. But in reality (under some conditions) they do see small amounts of liquid refrigerant from the evaporator anyway.

It is vitally important not to SLUG the compressor however. That said....the way to force feed the last few ounces is as follows:

1. Engine running, compressor on, AC set on high, fan on high, windows down.

2. Let engine and compressor run until the engine has reached normal operating temperature and the high and low side pressures have stabilized. Both Valves (high and low side) will be off at this point.

3. Hook up your can to the middle hose of your manifold gauge set and 'purge' that line a small amount.

4. Now fully open your middle service line valve. Depending on your manifold set it may have a valve on the manifold or you may only have a valve at the can tap/adapter. In any case...fully open that circuit.

5. Next (with can facing up/can tap accepting gas only) open your low side valve fully. Let low side gauge settle for a minute or so.

6. Now we begin the 'force feed'. Take the refrigerant can in hand and with quick, short rotations of the wrist....tilt it over about 90° so that a SMALL amount of liquid refrigerant gets sucked up. IF your manifold has a 'sight window' you will see a small amount of liquid refrigerant appear. As soon as you see liquid.... tilt the can back up vertically and wait for it to disappear.

You will see a sharp spike on the low side pressure gauge each time this happens. This is evidence the refrigerant reached the compressor. Continue to do this SLOWLY (it can take 15-minutes) to get 4-6 ounces in. Once you feel you have charged in the proper weight, turn off all valves let the unit run, check your pressures (now stabilized) and take a vent temp reading.

NOTES:

With very high ambient temps and in environments with high Solar Gain (Sun Belt States) a system achieving vent temps 30-35°F below the ambient is doing about it can do. And you should be quite happy with that. IF it does better than that (highway speeds, overcast, etc) great....but don't expect it.

Tip: When hooking up your manifold gauge hoses (to manifold and adapter) do NOT over-tighten. Just tighten snugly by hand. We don't want leaks obviously, but I see many people crushing the seals in either end. This eventually deforms the seal and it will block (partially or wholly) the line. You can almost expect this with rented equipment.

Disclaimer: Perform a 'force feed' at your own risk. I am not there to show you. Do so slowly and don't slug your compressor. Or if in doubt take it to a professional. It is an easily performed technique, done daily at shops and in driveways all over....but some folks can break an anvil with a rubber hammer. Just saying............

Worked like a charm, thanks! Another tip I learned (the hard way) for the future - take the weight of the new can PLUS the can tap (instead of just the full can) when trying to evaluate exactly how many ounces you've put in from the can.

 

[flintknapper]

Worked like a charm, thanks! Another tip I learned (the hard way) for the future - take the weight of the new can PLUS the can tap (instead of just the full can) when trying to evaluate exactly how many ounces you've put in from the can.

Good deal!

Next time you have a full recharge situation (starting with an empty system) let me know and I'll walk you through the process to introduce the first can of refrigerant (12-16 ozs) as a liquid through the high side (into vacuum). Will solve most charging issues.

Take care,

Flint.

 

[suprasvobodea]

Send your friend on an errand and while he is gone, charge your system.

Don't bother jumping the pressure switch (assuming it works OK now).

You are right, the system needs to have a minimum amount of pressure (usually about 30 psi) in order to satisfy the low pressure side of the binary switch (Pressure Switch). Your binary switch will not allow the compressor clutch to kick in if the pressure is too low or too high.

So how do we get refrigerant into the system if the compressor won't run?

We pull a vacuum on the system and let the vacuum suck the first 8-12ozs into the system.

Rather than walk you through the entire process I am just going to paste instructions that I made for another forum member here a couple of Summers ago. You can read through it and follow it verbatim or pick up at whatever point you are at now.

This addresses adding refrigerant to a system that has been evacuated (no Freon in the system). It assumes you have already added oil.

BE SURE you understand the procedure for charging the first can (as a liquid) into vacuum through the high side (ENGINE OFF). If you have any questions about it....ask here first.

A/C Pump Down and Recharge

​

• Before final pump down the system should be checked for leaks by first pulling a vacuum on the system for 15-20 minutes. Shut off manifold valves BEFORE turning off vacuum pump. If after 45 minutes there is no significant vacuum loss, you may assume there are no leaks and it is safe to proceed with pumping down the system in preparation for the recharge.
• It is important to pull a ‘deep’ vacuum on the system before recharging. This means a minimum of 1-1/2 to 2 hours. Your gauge will quickly pull into a negative reading (vacuum) BUT it takes time for any moisture to boil off and be removed from the system, so don’t rush this.
• Once you have waited the proper amount of time, turn off your low and high side valves while the vacuum pump is still running. This will help prevent the possibility of air getting back into the system (provided your lines and connections are good).
• Leave your high and low side lines hooked up to the A/C ports but remove the Yellow (center) line from your vacuum pump and connect your first can of refrigerant to it. Each and every time you connect a new can to the center line, you will need to ‘purge’ that line. We don’t want air/moisture going back into the system. So once the can is hooked up and pierced…crack the connection at the manifold just enough to let a small mist of refrigerant escape…then hand tighten it back. IF your manifold has a Schrader valve at the location, just depress it. That is what it is there for (purging the line).
• Now you are ready to introduce the first can of refrigerant as a liquid into the system. We are going to do this (FIRST CAN ONLY) through the high side. Since the system is under vacuum it will quite readily suck a good amount of refrigerant into the system just as it is (ENGINE OFF, COMPRESSOR OFF). Never open the high side line with the engine running and the compressor on.
• To charge into vacuum through the high side: Turn your refrigerant can upside down (point the end you have tapped toward the ground) so that ‘liquid’ refrigerant will enter the system when we open the high side valve. With the can inverted, open the high side (and ONLY the high side valve) all the way. The refrigerant will be sucked into the system within a couple of minutes (usually less). You will feel the can getting noticeably lighter and colder. Once you are confident the can has emptied, close the high side valve. We will NOT open the high side valve again during the remaining charging sequences.
• You now want to hand turn the compressor 8-10 full revolutions (belt should not be on yet or just loosely fitted). This will pump a small amount of refrigerant and oil through the system before we start it up. Then connect the belt and tighten it.
• The remaining refrigerant charge will be done through the low side, with the engine running, compressor on, A/C set to high and windows open.
• As before, connect a new can of refrigerant to the yellow center line of your gauge set and ‘purge’ the line. The refrigerant can MUST now be held upright so that only ‘gas’ enters the suction side of the compressor. We don’t want any liquid refrigerant going into the low side…since it is ‘possible’ to slug your compressor. There are a few exceptions to this warning…that I will cover later, but at this stage, the rule is: Only refrigerant in its gaseous state is to enter the compressors low side.
• Slowly open the low side valve (NOT ALL THE WAY) watch for the low side pressure to build…but not exceed 60-75lbs. Use the low side valve to control this. As the refrigerant is taken into the system (it takes a while, especially if it isn’t hot outside) you will be able to open the valve nearly all the way.
• After your second can has emptied (typical 12oz cans) you should have 24 ounces in the system. We want to shoot for 30-31 ounces total (can be adjusted later) so you will be using a part (roughly ½) of the third can. Expect the last bit of this charge to go in more slowly, be patient. This is also the time that we need to start paying attention to our gauge pressures and vent temperatures.
• Since we are basically ‘weighing in’ the refrigerant amount, we are in no fear of overcharging the system, but we want to find the point at which increasing system pressure no longer results in lower vent temps (diminishing returns).
• This is the point where I would like to be in communication with you. You may have questions…or I may need to ask you some.

General information:

*Make sure all valves are turned OFF before disconnecting or changing out refrigerant cans, we don’t want to lose any refrigerant charge or get air into the system.

*Pressure readings (for high and low side comparison) are taken with the Valves Closed. Some folks like to increase engine speed to 1200-1500 rpm to simulate high idle or just off idle speed, but there is no real advantage to this IMO. Just let the system stabilize (run at idle for 10 minutes) and note your pressures.

*Pressure readings will vary with the ambient (outside) temperature. So we will need to know the ambient temperature (or a good guess) in order for our pressures to mean anything.

*Each system…depending upon component condition and outside influences (heat loads from the environment) will work best at a specific charge level (a little less or more than the factor y spec). This is where the knowledgeable owner can take the time to ‘fine tune’ his system by adding or removing small amounts of refrigerant until you find the ‘sweet spot’ for your system.

*Your system (everyone’s system) will work better at highway speeds than at slower speeds or in stop and go traffic. Any time the compressor is turning faster and you have more air flow across the condenser (more heat exchange) the better the system will cool, so just expect that.

*If you can get vent temps that are 30-35° F below that of the ambient temp..then your system is working very well. You might get more than that…but the 80 series is hard to cool.

*Since you have taken the time to learn about you’re A/C system and equip yourself to work on it, you can now check it from time to time to see what your pressures are, trouble shoot it and work on it if needed.

***Lastly…I warned you never to let liquid refrigerant enter the low side of the compressor. In reality…you might have trouble getting the last few ounces of refrigerant into the system (especially in cooler weather). So it is permissible to quickly tilt the can on its side and then immediately back upright to let a LITTLE liquid into the system. The chances of slugging the compressor like this are exceedingly small. You will see the low side pressure jump/spike for just a second when you do this but generally it will not harm anything. Alternately, you can take a hair dryer and warm the can to force the last bit of charge into the system.

I have an 87 Supra that I replaced the compressor, condenser (all Denso -OEM) ) and the dryer . I’m trying to recharge & cannot get Freon 134a to enter system . The vacuum won’t go above 25 inches ( I know I should read 29) and after pausing it overnight it did drop about 4 pounds so I know I have a leak … somewhere . Is this why it won’t pull a charge into the new system ..?

Also , there are videos of people telling you to charge to the low system & turn the can upside down to make it go faster while running compressor! Why do they say this if it can damage the compressor by entering liquid into it from the low side???
what is the term “ slugging the compressor“ mean??

I’m a mechanical Engineer & have been working on this car for 35 years now.. I want to learn everything possible I can from my friends and fellow members of this forum

 

[gummycarbs]

there are videos of people telling you to charge to the low system & turn the can upside down to make it go faster while running compressor!

What videos did you find that say this? *Every* resource I read before doing my AC system said to do this *only with the engine off*.

what is the term “ slugging the compressor“ mean??

Same as getting water into your engine's air intake. An incompressible fluid can't be compressed by the compressor, so you break the compressor.

 

[BILT4ME]

I have an 87 Supra that I replaced the compressor, condenser (all Denso -OEM) ) and the dryer . I’m trying to recharge & cannot get Freon 134a to enter system . The vacuum won’t go above 25 inches ( I know I should read 29) and after pausing it overnight it did drop about 4 pounds so I know I have a leak … somewhere . Is this why it won’t pull a charge into the new system ..?

Also , there are videos of people telling you to charge to the low system & turn the can upside down to make it go faster while running compressor! Why do they say this if it can damage the compressor by entering liquid into it from the low side???
what is the term “ slugging the compressor“ mean??

I’m a mechanical Engineer & have been working on this car for 35 years now.. I want to learn everything possible I can from my friends and fellow members of this forum

On an automotive system, turning the can upside down with it running is a HELL NO situation.

You can do it if the engine is OFF. Then you must let the system sit and equalize for a period of time before turning it on.

Slugging the compressor means trying to force a liquid into a piston compressor and it will wreck it.

On a HOME AC system, yes you can do that. They have different operating systems.

 

[suprasvobodea]

Flint knapper
OMG.. Ok, Those vidoes are on UTUBE> . Just search on UTUBE for "recharging car ac system" THeres several on there!! I know I have a leak, as it drops slightly when I turn off the vacuum pump after 20 min (It's only 1.3 CF a rental ) & it only draws down to 25 " . ( i know I'm supposed to go to 29...) It's funny because I borrowed my friend's compressor to pressurize the system with the manifold gages on to 150 PSI and it held overnight to the same place on gages!!! But now, it won't pull lower than 25 " ... and I have a leak. I have dye in the compressor oil already, but it's useless if it's not under pressure. At this point, I'm raising the white flag and taking it to a local shop .. UNLESS.. you can talk me back from the cliff, and offer some constructive advice from here. ( I do NOT want to give up but I'm about exhausted & this is my first time doing a total rebuild on the AC system. Can I talk to you, or PM somehow? I don't know how to do that, and i don't want to give out my cell phone on this public forum. What should I do next .....?

 

[canman]

I’m a mechanical engineer with over a decade of experience with mobile HVAC. The system will take the refrigerant charge at 24” HG since the pressure in the refrigerant container will be roughly equivalent to the ambient temp in F. As you mentioned, unless you can achieve and maintain a vacuum of 29” HG, you have a leak, and there is no point in adding any refrigerant as it will eventually leak out.

 

[flintknapper]

Flint knapper
OMG.. Ok, Those vidoes are on UTUBE> . Just search on UTUBE for "recharging car ac system" THeres several on there!! I know I have a leak, as it drops slightly when I turn off the vacuum pump after 20 min (It's only 1.3 CF a rental ) & it only draws down to 25 " . ( i know I'm supposed to go to 29...) It's funny because I borrowed my friend's compressor to pressurize the system with the manifold gages on to 150 PSI and it held overnight to the same place on gages!!! But now, it won't pull lower than 25 " ... and I have a leak. I have dye in the compressor oil already, but it's useless if it's not under pressure. At this point, I'm raising the white flag and taking it to a local shop .. UNLESS.. you can talk me back from the cliff, and offer some constructive advice from here. ( I do NOT want to give up but I'm about exhausted & this is my first time doing a total rebuild on the AC system. Can I talk to you, or PM somehow? I don't know how to do that, and i don't want to give out my cell phone on this public forum. What should I do next .....?

So many unknowns here.

Please disregard the Youtube videos, often times they are not a good source for information with respect to Automotive A/C work.

At your elevation (Dallas) you should be able to achieve at least 28 inHg vacuum with a fully sealed system AND a good vacuum pump.

Rental pumps run the gamut from being good/usable equipment to worn out junk. Quite possible the vacuum pump itself won't let you get a deep vacuum on the system. IF the pump was a single stage type, worn...and did not have NEW/Fresh oil in it....then that is part of the problem right there.

System leaks are another possibility. While you replaced the Compressor, Condenser and Dryer....we don't know the condition of the Evaporator. It is not uncommon to have a small leak in the bottom corner of an evaporator. Typically debris collects in the bottom of the housing and gets soaked with the condensation produced there... leaving the bottom of the Evaporator sitting in mix of wet gunk. Naturally... this corrodes a spot in the Evap that usually presents as a small leak.

Until we know one way or the other whether the system is leaking (or not) it doesn't make good sense to go forward. Since some leaks can be difficult for the DIYer to find and address.....I would recommend (in this case) you take the vehicle to a reputable shop, tell them what you've done so far as see what they can find.

At that point....you can decide to let them do the work or take it back home and continue. IF the system will hold a vacuum then there is no reason why you can't charge the system yourself....BUT we still have a couple of unknowns (Condition of the Evaporator and TXV if so equipped). Hate to have you go through all the work only to end up with mediocre vent temps.

 

[gummycarbs]

It's funny because I borrowed my friend's compressor to pressurize the system with the manifold gages on to 150 PSI and it held overnight to the same place on gages!!! But now, it won't pull lower than 25 "

Sounds like a bad vacuum pump (or pump connection) or a seal that only seals under pressure.

 

[canman]

I’ve seen plenty of systems that will hold pressure but not a vacuum. Usually due to either a bad o-ring or improperly installed one. Same can happen to compressor shaft seals. When it comes to refrigerant systems and o-ring sealing performance, things really must be surgically clean. Always coat the o-rings with the appropriate compressor oil during installation.

 

[suprasvobodea]

So many unknowns here.

Please disregard the Youtube videos, often times they are not a good source for information with respect to Automotive A/C work.

At your elevation (Dallas) you should be able to achieve at least 28 inHg vacuum with a fully sealed system AND a good vacuum pump.

Rental pumps run the gamut from being good/usable equipment to worn out junk. Quite possible the vacuum pump itself won't let you get a deep vacuum on the system. IF the pump was a single stage type, worn...and did not have NEW/Fresh oil in it....then that is part of the problem right there.

System leaks are another possibility. While you replaced the Compressor, Condenser and Dryer....we don't know the condition of the Evaporator. It is not uncommon to have a small leak in the bottom corner of an evaporator. Typically debris collects in the bottom of the housing and gets soaked with the condensation produced there... leaving the bottom of the Evaporator sitting in mix of wet gunk. Naturally... this corrodes a spot in the Evap that usually presents as a small leak.

Until we know one way or the other whether the system is leaking (or not) it doesn't make good sense to go forward. Since some leaks can be difficult for the DIYer to find and address.....I would recommend (in this case) you take the vehicle to a reputable shop, tell them what you've done so far as see what they can find.

At that point....you can decide to let them do the work or take it back home and continue. IF the system will hold a vacuum then there is no reason why you can't charge the system yourself....BUT we still have a couple of unknowns (Condition of the Evaporator and TXV if so equipped). Hate to have you go through all the work only to end up with mediocre vent temps.

Flintknapper

Thank you for the help and detailed descriptions. I decided I am going to take my baby to a new shop that knows older cars.- like my 87 Supra. I am just going to have them LOCATE AND FIX the damn leak. Yes, I want to finish the job of recharging the system myself after they repair the leak. I will ask them to pull a vacuum with THEIR pump to see if they can get below 25". I will then connect up the manifold gages I rented and proceed to add 134A thru the high side as liquid with the car off.& low valve closed ) when I get home.
BEFORE i take over tomorrow , I think I'm going to start the engine, ( under vacuum) engage the dash switch and see if the clutch engages ...?? If it does, WHAT SHOULD I DO ?? - since it's not supposed to be below 30 and above ~ 290 or so ..?? ( not sure of the high side value) Please list the steps to determine if it's engaged with a brand new high/low press switch. Obviously - this is most likely an electrical ground or something issue! :-(

After checking/repairing the High /Low switch I will close both high/low manifold valves, start the engine, and turn on AC. Then slowly open the low side for the 2nd can of 134A - IN UPRIGHT POSITION for gas only !. My system takes 1.4-1.6 lbs of R12. That equates to 22 Oz of 134a. I found a thread on the SupraForum for a conversion from R12 >> 134A. They said to use 0.85 of the R12 amount + 0.25 oz. . I guess you are supposed to use LESS refrig for 134A, - not quite sure why ...