AC Vacuum sucks out the oil?

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Replaced my AC compressor few weeks ago due to a clutch going bad. I replaced it with a new Denso unit which come prefilled with oil. I vacuumed the system for about 30 minutes and then refilled with pure refrigerant. Can’t recall the exact amount but a bit more than two 12oz cans. I followed the FSM and made sure there were no bubbles in the sight glass at 1500 rpm. The dryer was replaced as well.

My question is, does pulling a vacuum draw out any PAG oil from the system? My AC doesn’t feel as cold as before and I’m not sure why, I thought that a vacuum on the system won’t remove the PAG oil but maybe I’m low on it?
Thanks
 

RoaringFork

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How did you recover the refrigerant before you replaced the compressor?

A proper A/C machine can drain some but not all of the oil from the system, done by vacuum.

When you vacuumed your system for 30 minutes did see any oil??
 

RoaringFork

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Excessive oil in the system can impede cooling. It’s possible the pre filled replacement compressor had more PAG than needed.
 
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How did you recover the refrigerant before you replaced the compressor?

A proper A/C machine can drain some but not all of the oil from the system, done by vacuum.

When you vacuumed your system for 30 minutes did see any oil??
Excessive oil in the system can impede cooling. It’s possible the pre filled replacement compressor had more PAG than needed.

I vacuumed the system with a harbor freight vacuum, I didn’t really see much oily mist come out of the vent.

I should mention that if I’m at idle in drive, and the AC compressor comes on, my rpm does dip about 200rpm for few seconds. I feel like it shouldn’t be that much.

Is there a way to recover all of the oil in the AC system?
 

RoaringFork

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Ideally... you would have drained the oil from the old compressor into a measuring cup, and record the amount. Then drain the new compressor and fill with the recorded amount.

How did you charge it, what refrigerant did you use? The problem you’re describing is: it’s not cooling as well... many factors other than PAG oil can cause poor cooling...

The compressor and dryer hold the majority of the oil. You could drain them both and compare to spec to see if it’s over filled. Or drain your old compressor, pull and drain your new compressor and see if it’s obviously overfilled.
 

flintknapper

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Replaced my AC compressor few weeks ago due to a clutch going bad. I replaced it with a new Denso unit which come prefilled with oil. I vacuumed the system for about 30 minutes and then refilled with pure refrigerant. Can’t recall the exact amount but a bit more than two 12oz cans. I followed the FSM and made sure there were no bubbles in the sight glass at 1500 rpm. The dryer was replaced as well.

My question is, does pulling a vacuum draw out any PAG oil from the system? My AC doesn’t feel as cold as before and I’m not sure why, I thought that a vacuum on the system won’t remove the PAG oil but maybe I’m low on it?
Thanks
The lubricating oil is carried through the system by the refrigerant. So when evacuating the system...you are also removing any miscible oil that way. But...there will remain a certain amount in low spots of your condenser, drier and evaporator. Pulling a Vacuum on the system (especially for just 30 minutes) will not remove much (if any) of that oil...and only then...if it had absorbed moisture.

As for the performance of your newly charged system, there are just too many unknowns for us to speculate why it is not cooling as well as before.

If you can share with us the procedure you used....perhaps we can draw some conclusions.

***

How much oil was in the new compressor? (8 ozs.?).
Did you replace the Drier?
Did you use a manifold gauge set to evacuate the system and recharge?
Did you use NEW vacuum pump oil in the vacuum pump?
How much refrigerant do you think you might have put in the system. (on a new install always weigh it in, then tailor the charge via pressure and vent temps). The sight glass is for when you are out in BFE and don't have anything else to gauge it by. Personally I think they should have left that part out of the FSM as it does more of a disservice to folks than helps.

As previously mentioned by @RoaringFork, too much oil in the system will prevent you from reaching the full cooling capability of the system.

But we are talking several ounces over before that comes into play.
 
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The lubricating oil is carried through the system by the refrigerant. So when evacuating the system...you are also removing any miscible oil that way. But...there will remain a certain amount in low spots of your condenser, drier and evaporator. Pulling a Vacuum on the system (especially for just 30 minutes) will not remove much (if any) of that oil...and only then...if it had absorbed moisture.

As for the performance of your newly charged system, there are just too many unknowns for us to speculate why it is not cooling as well as before.

If you can share with us the procedure you used....perhaps we can draw some conclusions.

***

How much oil was in the new compressor? (8 ozs.?).
Did you replace the Drier?
Did you use a manifold gauge set to evacuate the system and recharge?
Did you use NEW vacuum pump oil in the vacuum pump?
How much refrigerant do you think you might have put in the system. (on a new install always weigh it in, then tailor the charge via pressure and vent temps). The sight glass is for when you are out in BFE and don't have anything else to gauge it by. Personally I think they should have left that part out of the FSM as it does more of a disservice to folks than helps.

As previously mentioned by @RoaringFork, too much oil in the system will prevent you from reaching the full cooling capability of the system.

But we are talking several ounces over before that comes into play.
I did not measure oil in the new compressor because I did not want to contaminate it, and I didn’t anything to measure it with. Drier was replaced with new denso unit. Used new manifold gauges and new vacuum pump with new oil.
I refilled it with “pure” refrigerant - about 25-26oz At most.

I might try evacuating and recharging the system again
 

RoaringFork

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I did not measure oil in the new compressor because I did not want to contaminate it, and I didn’t anything to measure it with. Drier was replaced with new denso unit. Used new manifold gauges and new vacuum pump with new oil.
I refilled it with “pure” refrigerant - about 25-26oz At most.

I might try evacuating and recharging the system again

An evac and recharge may help. Where are you purchasing the “pure” refrigerant. That may be you’re issue... is it r134a, or the auto parts store blend that anyone off the street can buy? Do you have a 609?
 

flintknapper

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I did not measure oil in the new compressor because I did not want to contaminate it, and I didn’t anything to measure it with. Drier was replaced with new denso unit. Used new manifold gauges and new vacuum pump with new oil.
I refilled it with “pure” refrigerant - about 25-26oz At most.

I might try evacuating and recharging the system again
OK, thanks for the info...that helps.

Yes, lets evacuate the system and recharge. I am going to make one 'assumption' that the new compressor had an 8 oz. charge of PAG46 in it (most do) and that 'most' of the oil in your system prior to the recharge was gone. Full operating amount should be roughly 8ozs. but a little bit over will not be a big deal.

When you pull a vacuum this time...let it run for a good 2 hrs. That way we know you have a deep vacuum on the system (have boiled off any moisture, this takes time).

Be sure to purge your lines of air before introducing any refrigerant or you will be putting air into the system. Your previous charge was light (26 ozs.). You should be weighing in between 28-31 ozs.

Are you familiar with the procedure to charge the first can into the high side as a liquid (into vacuum, engine off)? If not...we can walk you through it. Or if you are not comfortable doing that...just recharge all refrigerant through the low side (gaseous) with the system running.

Do you have a temp gauge you can monitor vent temperatures with?

We will need to know the ambient temp when you do this...in order to tailor the vent temps.
 
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OK, thanks for the info...that helps.

Yes, lets evacuate the system and recharge. I am going to make one 'assumption' that the new compressor had an 8 oz. charge of PAG46 in it (most do) and that 'most' of the oil in your system prior to the recharge was gone. Full operating amount should be roughly 8ozs. but a little bit over will not be a big deal.

When you pull a vacuum this time...let it run for a good 2 hrs. That way we know you have a deep vacuum on the system (have boiled off any moisture, this takes time).

Be sure to purge your lines of air before introducing any refrigerant or you will be putting air into the system. Your previous charge was light (26 ozs.). You should be weighing in between 28-31 ozs.

Are you familiar with the procedure to charge the first can into the high side as a liquid (into vacuum, engine off)? If not...we can walk you through it. Or if you are not comfortable doing that...just recharge all refrigerant through the low side (gaseous) with the system running.

Do you have a temp gauge you can monitor vent temperatures with?

We will need to know the ambient temp when you do this...in order to tailor the vent temps.
Yes, my charge was on the light side but I stopped adding refrigerant because my high pressure side was at 230-240 and I didn’t want to push it. I’ve used this chart.
3C2E5274-E4F0-4744-B56C-5F29F1D4EA2B.png


I’m not familiar with discharging into high side first or what the purpose of that is. I do not have temp gauge but I can lick my finger
 

flintknapper

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Pressure/Temperature charts (interrelated) are useful when topping off a charge or for the purposes of fine tuning (optimizing) vent temps and troubleshooting. But anytime you are starting from an complete evacuation...ALWAYS figure on going by 'weight' and watch your gauges only for signs of over-pressure (indicating a restriction/other).

We know the system is designed to take between 28-31.5 ozs of refrigerant. So unless pressures (for ambient temp) get way outside of the normal 'window', plan on putting in the entire weighted amount.

Charging the first can into the high side as a liquid (into vacuum, engine off) insures you have at least 12 ozs in the system before you start up the compressor. It satisfies the minimum pressure needed to activate compressor's clutch and will get refrigerant flowing through the system the quickest. Remember...the lubricating oil is carried by the refrigerant. High side charging into vacuum is also the quickest way to get about 1/2 your capacity into the system.

But in this case...I'm not going to recommend it for you. I think you will benefit from doing a few system recharges...before using that method. There are a few things you could do that might get you into trouble, so let's wait until you are more experienced.
 

maxamillion2345

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A cheap digital kitchen scale works well for weighing your refrigerant.

Just for the record, Flintknapper is spot on with all his AC advice. Listen to him.
 
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