A/C question - won't hold vacuum but seems to hold pressure?

sabino56 · 10-11-2024, 01:07 PM

Hi, I'm looking for an answer to a curiosity and some advice

Background:
I had the bearing on the compressor pulley go bad. I had to evacuate the system as the A/C hard line runs in front of the pulley. I got the pulley off and replaced the bearing as others have explained in threads. I could pull a vacuum but it wouldn't hold with my little pump - but decided to let the shop who evacuated the system try regardless. They said - "big leak" somewhere.

I had replaced the o-ring on the one line I disconnected with the same purple one from BMW so my guess was it was the seal on the compressor shaft.
It's hard to pressure check in there so I bought a can of freon and some detection oil/dye and put that in the system. Sure enough, I could see some dye coming thru the pulley.

What is confusing/interesting to me is after letting it sit overnight I went out and the pressure (only 70psi static - one can) is still the same as last night. The A/C is actually cold/cool. Obviously there is some leaking under pressure as when running the A/C the dye became visible. I didn't have gage on high pressure side but obviously it was higher than the 70psi when not running.

Under vacuum I can pull to ~ 20-25 and watch it slowly bleed back to zero.

The curiosity:
It seems the seal which is leaking is directional - it holds pressure better than a vacuum?
I don't have a lot of A/C experience - a few fixes on various cars over the years but had not seen something where the pressure ~holds and the vacuum doesn't.
Is this "normal"?

Looking for Advice:
Regardless, it looks like I need to replaced the compressor. Any advice on something to avoid or brand to recommend?

If just the seal and the compressor hasn't grenaded - should I replace dryer also? and do I need to get system flushed?

Thanks

mainbearing · 10-12-2024, 10:33 AM

Sounds like the compressor shaft seal is leaking indeed. I would think the typical shaft seal would hold pressure better in one direction than the other.

Get a Denso compressor (check to see if you have a 5-rib or 6-rib pulley).
https://www.rockauto.com/en/catalog/...ompressor,6628

Or a compressor kit from UAC or GPD (incl expansion valve). Maybe with a new condenser too. Or pick up Denso parts individually.
https://www.rockauto.com/en/catalog/...nent+kit,17507

A new condenser should come with desiccant inside. However it is strange that the Denso table here says "Includes drier: No" (even if the receiver/dryer tube is part of the condenser and it should have the desiccant inside):
https://www.rockauto.com/en/moreinfo...t=6708&jsn=977

If the compressor has not granaded and sent debris into the system then no need to flush. It will be a guess as to how much oil to add, but do not overfill or it will reduce cooling performance.

Pick up a manifold gauge set (plus other things you might need) from Harbor Freight when on sale around $50 w/ coupon. Find Youtube videos on how to use.

Quote:

Originally Posted by sabino56

Looking for Advice:
Regardless, it looks like I need to replaced the compressor. Any advice on something to avoid or brand to recommend?

If just the seal and the compressor hasn't grenaded - should I replace dryer also? and do I need to get system flushed?

Thanks

gbalthrop · 10-12-2024, 12:27 PM

I'm NOT familiar with the Compressor Shaft or Seal, but it appears it is acting as a "Check-valve", where pressure can flow INTO the seal from Ambient air pressure, but has some resistance to pressure RELEASE from Refrigerant to Atmosphere. The question is: How LONG will it hold 70 PSIG from one can of refrigerant?

In AZ, I presume A/C is NOT optional, even with cool weather approaching?
If Seal "Seals" enough to hold pressure when compressor is NOT turning & pumping, does it leak when High Side pressure is 150PSIG or more? How Long do you intend to keep the car operational?

As far as desiccant replacement, the ISTA procedure is to replace it IF the system was open to the atmosphere > 24 hours. Early models, prior to 2009(?) had removable Desiccant cylinder in Condenser.

Lots of questions, NO Answers

George

sabino56 · Yesterday, 09:47 AM

Thanks, I appreciate the responses. Yeah, a working AC in the desert SW is a must though it’s cooling down so not so bad now. I’m going to replaced the compressor as any leak will eventually be a problem - even if apparently much worse under vacuum than under pressure.

The system has never been opened since new and spent its whole life in desert heat without any problems. Kinda frustrating that the bearing, meant to protect the belt/ability to keep engine going in the event the compressor seizes, goes bad and takes out a good compressor….. (that is, assuming the bad seal wasn’t going bad independently of the pulley falling apart).

I found TIS and read thru (should have done that before asking questions) and confirmed that desiccant is replaceable in the condenser for 2006 but you have to remove the radiator and condenser to get to it ( apparently comes out an opening in the top). So unless I find shavings in the oil when removing the compressor I’m not going to mess with that. I’ve kept it sealed up and it’s very dry here so when opened for short time shouldn’t be a problem.

I found a Denso compressor on FCP with same part number as the Denso in my car now plus made in Poland vs China so going that way.

Thanks again for the advice.

10-11-2024, 01:07 PM	#1
sabino56 Private First Class 87 Rep 150 Posts Drives: 2006 E90 330i Join Date: Mar 2018 Location: AZ, Tucson iTrader: (0)	A/C question - won't hold vacuum but seems to hold pressure? Hi, I'm looking for an answer to a curiosity and some advice Background: I had the bearing on the compressor pulley go bad. I had to evacuate the system as the A/C hard line runs in front of the pulley. I got the pulley off and replaced the bearing as others have explained in threads. I could pull a vacuum but it wouldn't hold with my little pump - but decided to let the shop who evacuated the system try regardless. They said - "big leak" somewhere. I had replaced the o-ring on the one line I disconnected with the same purple one from BMW so my guess was it was the seal on the compressor shaft. It's hard to pressure check in there so I bought a can of freon and some detection oil/dye and put that in the system. Sure enough, I could see some dye coming thru the pulley. What is confusing/interesting to me is after letting it sit overnight I went out and the pressure (only 70psi static - one can) is still the same as last night. The A/C is actually cold/cool. Obviously there is some leaking under pressure as when running the A/C the dye became visible. I didn't have gage on high pressure side but obviously it was higher than the 70psi when not running. Under vacuum I can pull to ~ 20-25 and watch it slowly bleed back to zero. The curiosity: It seems the seal which is leaking is directional - it holds pressure better than a vacuum? I don't have a lot of A/C experience - a few fixes on various cars over the years but had not seen something where the pressure ~holds and the vacuum doesn't. Is this "normal"? Looking for Advice: Regardless, it looks like I need to replaced the compressor. Any advice on something to avoid or brand to recommend? If just the seal and the compressor hasn't grenaded - should I replace dryer also? and do I need to get system flushed? Thanks
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10-12-2024, 12:27 PM	#3
gbalthrop Brigadier General 3028 Rep 4,373 Posts Drives: 2007 328xi E91 Join Date: May 2017 Location: Fairfax Co, VA iTrader: (0)	I'm NOT familiar with the Compressor Shaft or Seal, but it appears it is acting as a "Check-valve", where pressure can flow INTO the seal from Ambient air pressure, but has some resistance to pressure RELEASE from Refrigerant to Atmosphere. The question is: How LONG will it hold 70 PSIG from one can of refrigerant? In AZ, I presume A/C is NOT optional, even with cool weather approaching? If Seal "Seals" enough to hold pressure when compressor is NOT turning & pumping, does it leak when High Side pressure is 150PSIG or more? How Long do you intend to keep the car operational? As far as desiccant replacement, the ISTA procedure is to replace it IF the system was open to the atmosphere > 24 hours. Early models, prior to 2009(?) had removable Desiccant cylinder in Condenser. Lots of questions, NO Answers George
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Yesterday, 09:47 AM	#4
sabino56 Private First Class 87 Rep 150 Posts Drives: 2006 E90 330i Join Date: Mar 2018 Location: AZ, Tucson iTrader: (0)	Thanks, I appreciate the responses. Yeah, a working AC in the desert SW is a must though it’s cooling down so not so bad now. I’m going to replaced the compressor as any leak will eventually be a problem - even if apparently much worse under vacuum than under pressure. The system has never been opened since new and spent its whole life in desert heat without any problems. Kinda frustrating that the bearing, meant to protect the belt/ability to keep engine going in the event the compressor seizes, goes bad and takes out a good compressor….. (that is, assuming the bad seal wasn’t going bad independently of the pulley falling apart). I found TIS and read thru (should have done that before asking questions) and confirmed that desiccant is replaceable in the condenser for 2006 but you have to remove the radiator and condenser to get to it ( apparently comes out an opening in the top). So unless I find shavings in the oil when removing the compressor I’m not going to mess with that. I’ve kept it sealed up and it’s very dry here so when opened for short time shouldn’t be a problem. I found a Denso compressor on FCP with same part number as the Denso in my car now plus made in Poland vs China so going that way. Thanks again for the advice.
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