AC issues, can't figure out. (1 Viewer)

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Hi all.
I've been searching on the forum but couldn't find anything relevant to my issue.
AC air is coming out hot.
I rented the gauges to check pressure I got the following readings.
Static pressure (System off): 50 psi on both low and high ports
System on, engine idling: about 5psi on low port, close to 130psi on high
System on, engine at 2k rpm: low goes to the negative, high stays around 150 psi.
I assume I needed a recharge so bought the ac pro and followed their instructions.
Nothing... no change at all. I can't feel gas go8ng from the bottle to the system ( I did remove the safety cap)
Compressor clutch engages normally.

Any ideas?
 

flintknapper

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Hi all.
I've been searching on the forum but couldn't find anything relevant to my issue.
AC air is coming out hot.
I rented the gauges to check pressure I got the following readings.
Static pressure (System off): 50 psi on both low and high ports
System on, engine idling: about 5psi on low port, close to 130psi on high
System on, engine at 2k rpm: low goes to the negative, high stays around 150 psi.
I assume I needed a recharge so bought the ac pro and followed their instructions.
Nothing... no change at all. I can't feel gas go8ng from the bottle to the system ( I did remove the safety cap)
Compressor clutch engages normally.

Any ideas?

You have an obstruction in the system or the TXV is stuck closed. Do not fool with the refrigerant charge any further.
 

flintknapper

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What is the txv?

'TXV' =

Thermal Expansion Valve at the Evaporator. Known to become 'clogged' and present an obstruction and/or becomes stuck in various positions ranging from open to closed or anything in between. However....obstructions can occur elsewhere in the system...but that is clearly the issue in this case.

Finding WHERE it is and WHAT it is will be the challenge.
 

flintknapper

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@Leandro what else did u T-shoot? did u check the AC Fuse?

^^^^^

Not sure if you picked up on it....but the OP said he ran the system (meaning it works, electrically) but had abnormal low side pressure (and high side for that matter).

When you have low side pressure that low (or even going into vacuum) you have an obstruction, period.

He will need to find where that is and what caused it.
 

flintknapper

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Yes, system runs "normally". Blows air ( hot) clutch engages...

Any idea where to start?

System running (but not for too long, you don't have much oil circulating through the system) reach up and feel the small high side line where it goes into the evaporator at the fire wall. Line should be hot or very warm (don't grab it....just feel it).Then feel the larger low side line coming out of the evaporator and leading down to the compressor. Should feel cold.

IF the low side doesn't feel cold then your restriction is the TXV or evaporator. The TXV can seize up in the closed positon or the inlet screen in it can become clogged (usually with desiccant from the drier), but with other things as well. Do you have Rear Air?

Check back with your findings and we will go from there.

High Low 100.jpg
 
Last edited:
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Thanks for the info. I'll check that tomorrow, now I'm all dressed up to go for dinner. I can say for sure that the low side is at ambient temperature, I checked that multiple times while trying to charge the system. I haven't checked the high side though. I see refrigerant running thru the little peep window in the front, and I think I see bubbles, but moves so fast that I can't be sure.
 

flintknapper

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Thanks for the info. I'll check that tomorrow, now I'm all dressed up to go for dinner. I can say for sure that the low side is at ambient temperature, I checked that multiple times while trying to charge the system. I haven't checked the high side though. I see refrigerant running thru the little peep window in the front, and I think I see bubbles, but moves so fast that I can't be sure.

Sounds like classic obstruction....

Have a great dinner, the rest can wait.
 
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Ok, this gets more weird.
I ran tha AC for a couple of minutes following the gas citcuit and something doesn't add up (or I don't understand how the AC works as well as I thought).
The high pressure line going into the condenser (front, next to radiator) is pretty hot, so far so good. The high pressure line (thinner pipe) going along the driver fender and getting into the evaporator (thru firewall) is cold, maybe colder than ambient. The low pressure line coming out the firewall (thicker pipe with low pressure port) is ambient temperature.
I see refrigerant running on the glass.
Shouldn't all high pressure lines be hot until it gets into the evaporator, and low pressure lines be cold out of the evaporator? Could I have a blockage in the condenser instead of expansion valve?
 

flintknapper

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Ok, this gets more weird.
I ran tha AC for a couple of minutes following the gas citcuit and something doesn't add up (or I don't understand how the AC works as well as I thought).
The high pressure line going into the condenser (front, next to radiator) is pretty hot, so far so good. The high pressure line (thinner pipe) going along the driver fender and getting into the evaporator (thru firewall) is cold, maybe colder than ambient. The low pressure line coming out the firewall (thicker pipe with low pressure port) is ambient temperature.
I see refrigerant running on the glass.
Shouldn't all high pressure lines be hot until it gets into the evaporator, and low pressure lines be cold out of the evaporator? Could I have a blockage in the condenser instead of expansion valve?

The high pressure line(s) will be hot (to warm) depending on where you check them and and heat load. For instance if you feel the high pressure line anywhere it comes off of the compressor, over the top of the radiator and into the condenser...it will be HOT, like you can't keep your hand on it hot. If you check it at the sight glass....it should feel warm/hot, but not uncomfortably so. At the sight glass (on your vehicle) it splits off into two high side lines that trace the drivers side fender skirt and along the firewall. Anywhere along that course the line will just be warm.

The larger low side line coming out of the evaporator should feel cool to cold (depending on how long it has run and the heat load).

You need to let the system run a good 15-20 minutes to stabilize and allow some cooling of the interior. I would place the unit on recirculate, temp on COLD and fan on HIGH.

Then check your lines after it has run for awhile. We are just trying to get an idea where the blockage/restriction is.

Yes, it could be at the condenser. It could be at the drier. More commonly it will be the TXV at the Evaporator. IF the low side line coming out of the evaporator never gets cool and the pressure continues to be low or pull into vacuum then its a good bet the TXV or Evap is your trouble.

Just briefly....your A/C works by REMOVING hot air (and moisture) from the cabin. You are NOT bringing cool air IN, you are taking hot air OUT.

The absence of heat is of course what we define as 'cool'. The heat in the cabin is absorbed into the Evaporator and the Cold, Gaseous refrigerant. (Heat can only flow to a cooler source). The gas (and heat) then goes to the compressor, where it is compressed (raises pressure and temperature). It then flows as a hot gas to the Condenser where the heat (most of it) is released into the cooler outside air and the hot gas condenses into a liquid.

The liquid refrigerant goes through the drier (which actually stores some of it until needed), then it travels (still as a liquid) through the small line to the TXV (Thermal Expansion Valve) which meters how much of the liquid gets released into the Evaporator. When the liquid refrigerant (in reality not completely liquid at this point) is released into the Evaporator.....it is low pressure and turns back into a gas which is much cooler. The whole cycle starts again. The Evaporator absorbs more heat from the cabin.

Eventually you have enough heat exchanges that air in the cabin is feeling cooler AND the evaporator itself gets cold... so the air being blown across it aids in the cooling process. BUT the principle of Air Conditioning remains the same: You are removing heat, not bringing 'cold' inside.
 
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Did some more pinpoint troubleshooting today.
High line going into the condenser is flaming hot, untouchable.
The line that comes out to the rear AC is warm/hot up to the point where is capped (I capped it 3 years ago when the line going ander the truck fell into pieces)
The line that goes to the front AC, into the firewall is at ambient temperature.
This leads me to believe that the blockage must be somewhere in that line close to the condenser. If the blockage is in the valve or evaporator there were compressed gas on that line and be at least warm.
What do you guys think?
Should I start ripping off the lines and passing compressed air?
 

flintknapper

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Did some more pinpoint troubleshooting today.
High line going into the condenser is flaming hot, untouchable.
The line that comes out to the rear AC is warm/hot up to the point where is capped (I capped it 3 years ago when the line going ander the truck fell into pieces)
The line that goes to the front AC, into the firewall is at ambient temperature.
This leads me to believe that the blockage must be somewhere in that line close to the condenser. If the blockage is in the valve or evaporator there were compressed gas on that line and be at least warm.
What do you guys think?
Should I start ripping off the lines and passing compressed air?


Yes, unfortunately.

The high side lines (after the split off) should be a least warm to the touch. Not hot (depending on ambient temp and heat load) but certainly not ambient. Your restriction/blockage could still be at the TXV but you're going to have to "go in" either way....so might as well start at the condenser. It's possible the trouble is at your drier as well...if the desiccant bag has eroded. IF it did ....then you'll likely have blockage there (drier or line) AND at the TXV screen. The desiccant will look like fine silt.
 
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Did some more pinpoint troubleshooting today.
High line going into the condenser is flaming hot, untouchable.
The line that comes out to the rear AC is warm/hot up to the point where is capped (I capped it 3 years ago when the line going ander the truck fell into pieces)
The line that goes to the front AC, into the firewall is at ambient temperature.
This leads me to believe that the blockage must be somewhere in that line close to the condenser. If the blockage is in the valve or evaporator there were compressed gas on that line and be at least warm.
What do you guys think?
Should I start ripping off the lines and passing compressed air?
The drier is a part of the condenser - there is a plug that holds a long dissicant bag. Yep, one of those “do not eat” bags. Good idea to replace if cracking open the system for any length of time.

The block expansion valve (not a true TXV but same function) is the smallest restriction of the system. If clogged (with dissicant or crude) that is causing your problem. I don’t remember how accessible they are - but I did replace mine when I replaced the evaporator (do not need to remove the dash, just cut the small support below the glove box, I used a metal brace and 2 screws to fix).

No way around not cracking open the system - just dumping the refrigerant into the atmosphere not a great idea, see if a shop will do the recovery - having them do the charging is the easy route - Check with your local auto parts store to borrow a vacuum pump if you are going to tackle it yourself.

570DA89F-C204-4F8D-8542-65651C9B69B7.png
 
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Thank you guys
I had no time to keep working on this, just kept driving with the AC off and windows down.
I'm inclined to think my obstruction is either at beginning of the line that goes from the condenser to the evaporator or on the block where the peep glass is.
 

flintknapper

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Thank you guys
I had no time to keep working on this, just kept driving with the AC off and windows down.
I'm inclined to think my obstruction is either at beginning of the line that goes from the condenser to the evaporator or on the block where the peep glass is.

Guessing at this point is fruitless. You'll just have to disconnect some lines and run compressed air through them and the components (drier, Condenser, evaporator) in order to tell. Pain the rear....I know, but that's about all you can do.
 

flintknapper

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I know, I know.... I should stop procrastinating and get to it...
where is the drier located?


Passenger side of Condenser. It is a tube attached to the condenser. It contains the desiccant bag which might have ruptured in your case.

Once the system has been evacuated (refrigerant)....you can remove the plug at the bottom of the drier and remove the contents. You'll be doing this anyway because you know the desiccant in there now (if still intact) is old and anytime you open the system to atmosphere for very long, you need to replace it anyway.

Desiccant Tube.jpg
 

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