worf928

FYFI: (for your future information)

Nylog: acsource.com

Compressor seals - at least the shaft seal - should be replaced.

Big Black o-rings for the top of the compressor are for the "Service Manifold" (aka vehicle-specific adaptor plates.)

They are not o-rings on the 90+ 10-cylinder compressors; the single gasket is very weird and part of the gasket kit (from acsource.com)

worf928

Last, I'm not so-sure that pressurizing the system to 300 PSI is a great idea. That is higher than the operating high-side pressure and the low-side components should never see pressure greater than 120-ish PSI (IMHO) when the AC is switched off.

The evaporators like to develop leaks all on their own and don't need extra help with that.

Bilal928S4

Dave,
So I have replaced all the O rings and still a have a leak somewhere that I cannot hear. I only pumped it up to 190 psi and it drops really fast, in a couple of hours I was down to 150, but then last night it was 125 and this morning it was 122.
So I will try and put some soapy solution to all the joints again. Not hopeful.
How bad is it to change the front compressor seal?

j.kenzie@sbcglobal.net

Nice job, Bilal. I did the same thing on my 84. I am surprised that there are no o-rings at the compressor plates. Some of those old rings of yours look pretty beat up. Good thing you did this.
Dave

worf928

Spray every nook and crany of the compressor, the clutch, the service manfolds, and hose connections. I'll bet the service manifold is leaking along with the shaft seal.

There are 24 o-rings (14 front, 10 rear) not including seals for the compressor or seals for the service ports themselves. (And one more front one on '87)

The hardest part is getting it clean. It has to be pristine or you'll get grit in the guts. The seal kits are available from acsource. (And there's a cheap book you can get with directions.)

worf928

Those are the service manifold o-rings for the 6-cylinder (pre-90-ish) compressor. The 10 cylinder uses one bizarre rubber gasket instead of 4 o-rings.

worf928

Nylon is great stuff. Blue is for r134. Red is for r12.

Bilal928S4

I called the manufacturer of nylog and was told the blue can be used for both R-12 and R-134, but red only for R-12.
Therefore, I used nylog blue.

dprantl

This is the seal under the manifold of the 10PA20C:



When you have a good refrigerant charge, leave the car overnight, then in the morning before you insert the key into the ignition, set the fan speed to '1', then start the car, put your nose right up against the center vent and turn the top climate control slider to the square. It's hard to describe, but if you smell a "musty" smell that goes away after a couple of seconds, it's possible that your evaporator is leaking.

Dan
'91 928GT S/C 475hp/460lb.ft

Bilal928S4

Yep. That is the seal I found under the plate. I coated both sides of it with nylog blue and closed it up.

GeorgeM

Make sure you check the rear evaporator for leaks where the copper tubes attach to the radiator. They're crimped with some sealant on the inside, which melts and leaks out when heated, so repair is difficult if not impossible, although some have had luck with "muggy weld' or similar. I got a used one from 928Int'l and it was leak free.

That yellow stuff around the joint in the pic is dye.

Do you intend to stay with R12?

Bilal928S4

I had checked all the connections at the rear AC before I embarked on the O-ring replacement odyssey. Yes I am trying to stay with R 12.

WallyP

Years ago, it was a common practice to fix a leaking GM evaporator (which was made in a similar manner to our rear evaporator, and which failed often at the multitude of joints) by cleaning the ends with the multiple joints, then potting the entire end in an epoxy compound. Might work with the rear evaporator.

Capt'n Earl liked to remove the rear evaporator, clean the ends really well, pull a good vacuum, and wick a specific Loctite product into each of the joints. I don't remember the product number.

I would be tempted to fix a leaking unit with both procedures - the belt and braces approach.

fraggle

I found the company in Texas that developed the GM process, but they would not return my calls. I wanted to get my rear evap rebuilt that way.

Capt'n Earl has the next best, and likely only, other method. I don't know which product he used, but when my rear AC starts leaking again, I'll use that method.

Bilal928S4

Ok. I spent the evening spraying soapy water all over the joints. Could not find a leak, I then sprayed the shrader valve and it was leaking. I thought wow found the culprit and it will be an easy fix. I went to my parts bin but could not find a shrader valve. So did the next best thing and put a cap on it.
Pressurized the system again to 200 and thought I am home free, but to my dismay saw the needle go down.
So took the top portion of the rear console out again and started spraying everything including the various connections and the evaporator coil but nothing. I even sprayed and soaked the condenser and no bubbles.
So now it is either the compressor shaft seal or the front evaporator coil. Took the compressor off and got the nut for the clutch off. To do that you have to take one if the hose connections off, use the air gun to take the front nut of the clutch off, remove the clutch, put the hose back in and then pressurize the system. Sprayed the reinstalled hose connection, no bubbles. Sprayed the shaft seal no bubbles. Now I am getting pissed and soaked with the soapy water while laying under the car. Thinking that now I have to take the whole dash off to change the evaporator.
As I am looking at the compressor I see that the water has dripped to the rear of the compressor and bubbles are forming. So I found my leak it is in the rear of the compressor housing.
So now where can I get the cheapest price for a new compressor?
It is for a 1991 GT part number 928 126 113 00.