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Old 07-18-2016, 06:31 PM   #1
samadams9
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Default Intermittent AC problem - doesn't work when the engine is cold?

The car is 2007 Subaru Impreza SOHC with manual AC, with 220,000 miles.

The symptom is that the AC works intermittently, seemingly only works only when the engine is really warmed up. It does not work first in the morning or cooler evenings. This seems opposite of the most AC symptoms out there in various forums.

What was done before this happened was that the high pressure discharge hose had a leak, and I replaced with the new OEM hose, replaced the receiver drier, added 2ml PAG mid viscosity oil. I used the manifold gauge and the vacuum pump from Autozone and did the evacuation procedure.

The system holds vacuum fine, no vacuum loss for 20 min after the pump is shut off.

So, I went ahead and charged the system with R-134 (Factory spec 16 to 19 oz). I actually measured the weight of the cans during the charge so I'd stop at about 17 or 18 oz of freon in the system, excluding the small amount I bled out of the manifold hoses before opening the ports.

Everything went well and the air was cold. The pressure read about 25 psi low side, 205 psi high side, 77F ambient temperature. (Factory spec: 18 - 28 psi low side, 213 - 242 psi high side, with 85F ambient)
As I've done this successfully before on other cars, I thought the problem was fixed.

But next morning the AC didn't turn on immediately. What I observed was the AC turns on after driving for 15 min or so, (like it has to be warm enough that the radiator fan turns on by itself). Once it works it blows at about 45F. And it works as long as I don't let the car sit more than 2 hours. It's been like this for about a week.

What's causing this? System contamination? Over or under charged freon? Faulty expansion valve? Is some kind of a temperature sensor at play here?
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Old 07-18-2016, 09:24 PM   #2
Endika
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Do you hear the compressor and fans kick on in the morning/cold starts?
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Old 07-19-2016, 03:15 AM   #3
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Quote:
Originally Posted by Endika View Post
Do you hear the compressor and fans kick on in the morning/cold starts?
When in the morning/ evening, when I press the AC switch on, the fan comes on but the compressor doesn't, with warm air coming out (not the heated air but lukewarm.) I see the pulley is not spinning.

When the AC works, yes I can hear the compressor kicks in along with the fan.
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Old 07-19-2016, 08:26 PM   #4
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with the car cold and the ac on try tapping the clutch with a screwdriver or small hammer
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Old 07-20-2016, 05:34 PM   #5
MikeSomething
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I have an '08 WRX with the same exact problem... I'm thinking it's the compressor clutch that's bad.
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Old 07-20-2016, 06:54 PM   #6
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Quote:
Originally Posted by Endika View Post
with the car cold and the ac on try tapping the clutch with a screwdriver or small hammer
I tapped the clutch. I'm not sure what I'm looking for but nothing happened.
I kind of felt around the compressor clutch but nothing seems too loose or too tight.
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Old 07-20-2016, 10:21 PM   #7
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@MikeSomething
Why do you think it may be the compressor clutch? I just don't get why the AC works when the engine is fully warmed. Something is not sensing the pressure correctly?
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Old 07-22-2016, 09:25 AM   #8
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@samadams9...
The spring on mine is probably shot. It kicks the compressor on randomly throughout when I'm driving...
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Old 07-23-2016, 01:17 PM   #9
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Hmm I started to think I'd replace the expansion valve before messing with/ spending money on the compressor. The valve might be the cause of blowing the high pressure hose in the first place...

Also, although I couldn't find in Subaru manual I have, other articles from this forum and others say receiver/ drier replacement should be done with addition of 10 ml oil. I guess I should add another 8 ml?, as I added 2 ml out my guess for lost oil from the hose leak (did have small oil smudge around the leak)

Last edited by samadams9; 07-23-2016 at 02:50 PM.
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Old 07-23-2016, 04:48 PM   #10
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So I went to a local shop for consultation. The Ac was working at the time, and the mechanic says he won't know exactly what's wrong until he tests circuits or hook up to the machine, and at that point he'd have to charge me, but from what I explained, the guy was cool enough to give me an advice.

First, he thinks I overfilled the ac oil. Extremely excessive ac oil can prevent from charging proper amount of freon, making the ac system act like undercharged though the pressure reading may be fine.

But I think in my case, if anything, the oil is under filled. (he still thinks I did overfill)

Also, it's less likely but possible that the expansion valve is stuck open. It didn't make sense to me but the heat in the engine compartment somehow helps normalize the pressure in the system for the compressor to kick on.

Finally, the compressor/ clutch malfunction is a possibility but he needs to do the test.

I think my next course of action is to replace the expansion valve. If no luck, I might just have to let this shop guy handle it...unless someone has a better idea.
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Old 07-24-2016, 07:56 AM   #11
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Quote:
Originally Posted by MikeSomething View Post
I have an '08 WRX with the same exact problem... I'm thinking it's the compressor clutch that's bad.
The plate wears down & the gap becomes to big, the clutch starts to slip.

Mine does that, and I get like 2.8 knock when it cycles on.

Yesterday I removed the bolt in the front, slid the front plate/spring thing off, and there were 2 shims behind it. I removed the small one. It's much better now, but the gap is still to big. I have a rebuild kit coming in a few days, hopefully with more shims to get the gap down a bit more.

(It was a bitch to get off the first time. I PB blasted it for a bit, then used two screwdrivers to work it off. It slides on and off easily after I cleaned & anti seized it up. You can do this with it all hooked up in the car, no need to remove belt or anything. I didn't have a big enough pair of channel lock pliers, but you could probably grab that triangle center part & wiggle it off easier)

The older compressors have 3 threaded holes in the front cover. You can get 3, 5 mm x 30 (.8) bolts and screw them in slowly & evenly to press the front cover off.

Factory spec on that gap is something like .15mm to .4mm. Mine was over .7mm Just stick a feeler guage in there and see how big yours is.

Last edited by point78; 07-24-2016 at 08:04 AM.
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Old 08-20-2016, 04:46 PM   #12
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So, the quick update on my car is that the ac issue hasn't been fixed.
Again, the symptom is that the ac compressor clutch engages only when the engine is fully warmed. And once it start working it works consistently until the engine is cooled.

What I did this time:
AC compressor clutch shimming - didn't work:
I'm not super confident with feeler gauges but the clutch gap was about .56mm or so. I took one washer out and the gap was about .44 or so. But the compressor does not kick on. I took out up to 3 washers, but the same result. I put two back on so right now the gap is at .44mm which should be good.

Expansion valve replacement - Didn't work:
It made no difference at all and was a waste of time and $20 (i recommend to always get oem o rings)

Again I evacuated the system and checked for leaks, and things are good there.

So, from what I know/ heard, I'm left with the possibility of system contamination possibly too much oil in it. The only thing I can think of that would cause this is that a lot of ac oil was left in the manifold gauge/ hoses when I rented it from Autozone and that got fed into the system when I charged with freon. But i doubt that much oil can stay in the manifold gauge/ hoses. Not sure about this one.

Any feedback or tips would be much appreciated.
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Old 05-17-2022, 11:39 PM   #13
treboRX
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Default AC clutch shims

I know this is a super old thread but where did you get all those shims? I got a new clutch and I have no shims in my old one or the new one
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Old 05-18-2022, 09:41 AM   #14
Elbert Bass
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Quote:
Originally Posted by treboRX View Post
I know this is a super old thread but where did you get all those shims? I got a new clutch and I have no shims in my old one or the new one
I can't recall ever installing a clutch kit that didn't come with a new bolt, a bag of shims, and all the snap rings.
You must have either been sold an opened box or a really cheap POS part...
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Old 05-20-2022, 05:12 PM   #15
treboRX
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Default Air gap shims/clutch kit

First off, thank you for replying on such an old thread. I'm just having a problem finding any kind of info. I know my compressor is good. I fried my clutch because it needed to be him apparently. I guess bought a beat one. It had the disc, snap rings and the electro magnet that came with the wrong wiring clip. But so does every other one you can find online. Do you have any recommendations or is it too long ago to remember? I want to give it one last shot before I go and buy a whole compressor. Cuz then I have to get it evaced. I can install. But if I'm putting new R134 I would much rather a shop do it. And that'll really hurt your pocket... Thank You again for your time.
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Old 05-22-2022, 12:18 PM   #16
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Have you contacted where you bought the part?
only other options: Try an auto parts store - automotive a/c repair/installation shop - a refrigerated truck service shop like Thermoking - on-line A/c supply company.
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