User 52121

Alright so I've got my dad helping me on this (former GM master service technician) because I'm not too up on how A/C systems function.

The compressor on my car was leaking, so 2 winters ago I swapped in a brand new compressor and drier. Recharged the system (R12 - woo hoo!) and for the last year and a half it's been awesome. 42.5 degrees coming out of the vents on a 90 degree day ain't too bad...

So a few weeks ago (Memorial Day weekend), did a DE up at Road America. Used the A/C on the way up to the track, it worked great. After the first day of DE, while taking the car into town to put fuel in it, it was hot so I flipped the A/C on, and noticed it didn't work anymore. Now I share the car with my wife, and she's always complaining "it's hot", and I suspected she ran the A/C during one of her sessions. I've since learned there is no WOT cutoff switch for the A/C on the 944... and my dad tells me there is usually a high pressure blowoff valve in the system, which pops if the system becomes over-pressurized and dumps all the freon (to prevent damaging the compressor). Running a car at a DE with sustained high RPM for a long time while running the A/C could certainly generate high pressures in the system.

We believed, at the time, this is what happened because after the DE weekend, I hooked up the gauges, and there was barely 10psi in the system. Recharged it, seemed to hold pressure (left the gauges hooked up over night and everything stayed full) and figured we were good to go (A/C ice cold again.)

We've had mid-90s all this week here in Chicago, I've been driving the car to work (and using the A/C every day). Used it last night on the trip home, worked great... ice cold, as always.

Parked the car overnight, ~10 hours later, heading into the office this morning, go to flip it on... and it's not working anymore.

My dad is asking to check around the "high pressure blowoff valve" to see if it's wet. From what I can see from Clark's Garage and the FSMs, there is no such thing. Does such a valve exist?

With the little A/C experience I have... it seems usually systems just don't cool "as well" for a while if they have a leak. I've never run into a situation like this where one day it's ICE COLD and the next day it's NOTHING.

Any ideas?

UPDATE------

Found the leak. The compressor is leaking where the rear portion of the compressor body mates to the main portion of the compressor body. I added some UV dye to the system, ran it for a few days, then looked around with a UV light. Right at the seam in the A/C compressor body where the rear cover connects is all bright yellow.

The compressor is only 2 years old. Damn. Anybody have any opinions on the "retrofit" compressor that Zim's sells?

http://www.allzim.com/cgi/sh000001.p...%23a9537#a9537

86 951 Driver

Is your compressor kicking on when you hit the button?

Do you still have pressure in the system?

To leak all the freon out overnight is a decent sized leak, and with R12 being hard to get and expensive you probably don't want to leak it out all the time.

John_AZ

No "blowoff vlave" there is a safety switch on late models:

http://www.paragon-products.com/Airc....821.36.51.htm

You have a leak. I use an electronic sniffer and your dad has more knowledge than I do in finding freon leaks.

GL
John

xsboost90

no blow off in any system I've ever heard of. You would have a high pressure switch, which would sense high pressures in the liquid line and turn the compressor off, and a low pressure switch which senses low pressure on the suction line and shuts the compressor off. You most likely have a leak, prob. the o-rings on the compressor.

white924s

If the freon were leaking out, would it be apparent from the sight glass on the drier? I've heard that that can have bubbles or get cloudy if the A/C system is low on pressure.

I ask because my car also has a new compressor (but R134) and my A/C recently stopped blowing cold air. This may be a dumb question, but do the expansion valves in these cars ever fail?

John_AZ

YES with R-12. Bubbles indicate low freon if the RD receiver Drier has a sight glass..
NO with R134a does not have this indication and the R134a RD receiver drier does not have a sight glass.

Yes expansion valves fail due to contaminated systems and poor charge.

The expansion valve can have a blockage-dirt (contamination) or freeze -ice and block the freon if the system is not properly maintained.

John

User 52121

Thanks guys. I'll borrow a sniffer from a friend of mine and see if I can find the leak.

Would have been nice to have A/C yesterday on the 3hr drive home from autocross in 90-degree heat!

86 951 Driver

Did you check the pressures yet?

User 52121

Whoops... totally did not realize I hadn't responded with that yet.

Yes, I checked pressures. Definitely low, though less low than I expected. After Road America I had 10psi on the high side and pretty much nothing on the low. After checking it last Thursday, I had 10psi on the low side and ~90 on the high. Put a little more in Thursday night (hoping it would at least hold until Sunday since I knew it was going to be hot, and I'd have a long drive home after Autocross) and... I guess it didn't hold. Down to 80psi on the high side now.

Definitely leaking somewhere now. If I had to wager a guess, I'd say I've got a hole in the condenser, for the simple fact that the A/C worked 100% awesome (and held it's charge for over a year!) right up until the car hit the track. My guess is a rock got kicked up and put a hole in it. Hopefully the sniffer tool will find it.

djantlive

i would convert to r134. it'll be easier and less costly to charge the system.

get a sniffer to identify the leak. have an ac shop evac and charge it properly after the leak is fixed.

Ben951S

Freeze12 is awesome btw. Use dieselgiant, best price and don't need the cert.

User 52121

UPDATE------

Found the leak. The compressor is leaking where the rear portion of the compressor body mates to the main portion of the compressor body. I added some UV dye to the system, ran it for a few days, then looked around with a UV light. Right at the seam in the A/C compressor body where the rear cover connects is all bright yellow.

The compressor is only 2 years old. Damn. Looks like I'll need another one. I'm pretty sure I bought this one from 944online.com, it was $250 for the reman unit + $200 core... now they're $545 and no core.

Anybody have any opinions on the "retrofit" compressor that Zim's sells? I did a search and can't find a single hit....

http://www.allzim.com/cgi/sh000001.p...%23a9537#a9537

86 951 Driver

There is a company on ebay that sells rebuilt compressors. I used them and haven't really had an issue yet. Although my car has been down for a couple of weeks again.

John_AZ

You can DIY and rebuild your compressor.
It should be OK inside since it was rebuilt 2 years ago--good valves and cylinders.

This is one example of a kit you can get:
http://www.griffiths.com/shop/index....roducts_id=190

You may find a local AC tech to help. There are also a few RL members who rebuild for around $100- $125 plus $50 s/h round trip.

You can save the money and DIY

Here is a DIY on a compressor JIK
http://www.944time.com/porsche/2007i...5C-rebuild.pdf

GL
John

spanky

HP switch only, shuts down compressor. You never dump freon in to the air.