Gary Gaukler

Wondering if one of you A/C experts can help me diagnose this problem: The A/C (R134a) in my 1986 951 does not cool at all. It was converted by the previous owner's shop to R134a in 2002. When I bought the car in 2003, the A/C didn't work, and I never bothered to deal with it until now.

Last week I recharged the system from a bottle, and the low side pressure is at around 40psi. I don't have the appropriate gauge to check the high side pressure. Compressor clutch engages correctly when I hit the snowflake button. I can see refrigerant flowing in the receiver/drier sightglass when the compressor runs. But still no cooling at all.

Can I conclude from this that something must be wrong with either the evaporator or the expansion valve, or could it still be the compressor? I'd like to rule everything else out before I tear out the dash to get to the expansion valve...

Thank you in advance for any insight that you can provide!

Gary

joonas

http://www.clarks-garage.com/shop-manual/hvac-02.htm

Does it blow hot or outside temparature air when A/C is switched off?

Gary Gaukler

Thanks for the link; I had been using Clarks Garage to try to make sense of this, but can't

The vents blow outside temperature air both when the AC is off or on (with the temperature **** on cold).

Thanks,
Gary

dnwong

I have the same problem with my A/C and it was converted with one of those auto parts store kits. But really have not spent much time looking at it. I was thinking about vac the whole system out and putting back Freeze-12 into the system.

xsboost90

you need to fill the system until all the bubbling in the sight glass is gone. You must have just enough to trip the compressor on but not enough to actually cool much - IIRC you'd be upwards of 60psi on the low side in TX. They take two pounds or usually two cans roughly to clear the sightglass.

Gary Gaukler

So this morning I invested $40 in a set of A/C gauges. Now I am more confused than ever...

With engine off, both low and high side measured around 40psi. With the car running and A/C on, the low side pressure was 0 (actually a very slight vacuum), and the high side pressure about 50-60psi or so.

So then I filled in some more refrigerant (a little less than one pound). After I was done with one can, the pressures with A/C on were 20psi (low side) and 230psi (high side). Still no cooling though...

But now the pressure with engine off is around 110psi on low and high side - is this okay?

Should I just add more refrigerant at this time? I am not sure how much refrigerant was in the system when I started messing with things... my assumption was that it was empty.

xsboost90

did you ever look at the sight glass- round glass eye below the ds headlight? Your gauges will have a red/blue line- the blue going to the larger line and the red going to the smaller. The smaller(red gauge) should be showing in the mid 200 range and your blue side (suction line) around 40-45 or so- only works when the car is running! So start the car, put the gauges on- look at the sight glass w/ a flash light. Turn the a/c on high w/ the fans on high and open all the vents. If the compressor kicks on look at the sight glass and see if its bubbling. Open the low side(blue) only slightly and turn the can upside down and shake slowly while filling- dont dump it in too fast. Your sight glass should stop bubbling when the system is full. did you vac the system down before you charged it? If not you would need to do so or its got air in the system.

CurtP

60 PSI on the low side?! That's over pressurized if you're talking 134a. Normal operating range is 25-45 PSI. 30-35 PSI gave me the best results. Going higher won't make the AC work better.

With the compressors off, it is normal for the two sides to equalize.

There's a A/C maintenance thread in the 944 Turbo forum that may be of help to you Gary.

Gary Gaukler

Thank you all for the advice! I put more refrigerant into the system, and now it actually does blow cold air. That is the good news.

The bad news is that at anything above idle rpm, the car makes a horrible screeching sound that is coming either from the alternator or from the A/C compressor. When that sound happens, the voltage indicated in the dash drops fairly significantly, from maybe 14V to 12V - as if the alternator was not putting out any voltage. The sound only happens with the A/C on.

I used to get this kind of sound before, but only for a short while when I would start the car after it's been raining. I assumed it was a belt slipping, but now since it does it all the time (above idle) when the A/C is on, I suspect it is the compressor.

What do you think?

Thanks,
Gary

PeteL

loose belt

Zero10

its a loose belt. You were right, now go tighten it

mtccl

probably a loose belt because now the compressor is really engaging and cooling. I would have evacuated the system to make sure all moisture was out of there or you can damage the compressor. I did read you said it had a vacuum on it so that is a little reassuring. When I first start messing with A/C about 10 years ago I didn't vacuum and the compressor ran great for 2 weeks and then blew a huge hole in the side of the compressor. Since then I've always started with a vacuum and no problems with DIY's on A/C. Your gauge readings are in the ballpark when running. They mean nothing to me when car isn't running.

Gary Gaukler

I confess I do feel slightly stupid now. It was indeed the belt... tightened it, the screech is gone and everything works.

It's awesome to have working A/C after 5 years

Thanks again for all the help!

Gary