1993 and older R12 R4 compressors vs. newer R134a R4 compressors

[WarWagon]

Apparently the R-12 version of the R4 is no longer made "new" and rebuilds are 50/50 odds of having the proper 'level' port height to match the R12 manifold hoses. R134a compressors are substituted as new to retrofit the R12 system compressor part numbers with different height sealing washers.

The R134a compressor has a 1/8" step in on the high side port. The R12 compressor design ports are even.

The cure is to use the newer R134a compressors is sealing washers that are different thickness. As usual the proper parts are NOT included. You will need:

A/C Manifold Seal Kit
Part #: 15-20058
GM Part #: 02724887

Word is to use the green seal for the pressure side and the yellow seal for the suction side. I am not interested in trying this.

When I first got this truck the sealing washers would blow out on hot days after working perfectly for vac and pressure tests. I replaced the compressor to solve the problem with a reman. After that one went bad I tried the R134a version again and had it blow out yet again. Makes a nice $40 cloud... :mad2: I wasted a lot of freon trying to get this to work with a lot of long hot drives after the system blew out a washer. I suspect the higher head pressures of 121 degree days would blow out the proper combo of washers. The wrong combo will hold and blow out at lower temps.

I will 'patch' the problem with yet another reman that has the proper port heights as I already had the hoses rebuilt 3 years ago. I don't recommend this as the reman unit clutch broke (and was repaired) and the the body started leaking causing it to burn up from low freon and oil at 2 years old. Reman R4's are known low quality.

I suggest the best option is to obtain the newer R134a hose set if available or get a R134a manifold and have your hose set rebuilt with it. Only the 134a version of the compressor is available new now and the R12 part number new comes with the WRONG/MISSING sealing washers for our trucks. (Missing yellow.)

 

[THEFERMANATOR]

Theres a GM TSB somewhere regarding this as starting in 93 ALL trucks wether R-12 or R-134 got the new stepped style hookup. I have yet to see a problem with the GM washers when installed correctly. I've put them into systems before with plugged orifices and tripped the high pressure switch without a seal failure(350+ PSI).

 

[WarWagon]

Supposed to be like 1.2 MM clearance between the manifold and compressor when installed with the correct parts. I assume I don't have enough and I am unloading the seals when parts expand when hot. Looks like I can't find one of the old rebuilt units to use again so I am going to have to get extreme. Maybe the manifold is bent.

 

[THEFERMANATOR]

Supposed to be like 1.2 MM clearance between the manifold and compressor when installed with the correct parts. I assume I don't have enough and I am unloading the seals when parts expand when hot. Looks like I can't find one of the old rebuilt units to use again so I am going to have to get extreme. Maybe the manifold is bent.

If you put the manifold on with the wrong seals it will warp the manifold atatching point and may never seal again. In the past I have stacked the thin sealing washers to get the desired thickness, but it isn't a long term seal as all the rubber stacked up will cause issues after a few years.

 

[WarWagon]

Where do I put the straight edge to check for this kind of warping and is that test even possible?

 

[THEFERMANATOR]

You can use a straight edge and a micrometer to see if it is flat or not.

 

[WarWagon]

So far so good at 112 degrees out and revving to 2K in the parking lot to cool it down with a VOV orface tube.

Appears the trick is to use the thickest discharge washer and the thick suction side seal. The heights don't look even on the back of the compressor when you set the washers in - but it works.

 

[WarWagon]

Fail! issed: Here we go again with a cloud of R134a and oil blown everywhere under the hood. I will double check the safety vent didn't pop off. (Sure acts like it.) Otherwise it is the same area blowing out and resealing.

I will replace the high side cut out switch (again) in case it is bad. It will also get a set of 1994 hoses with the stepped block.

Apparently starting the engine with everything heatsoaked causes high high side pressure. The switch should protect the system from this.

 

[Will L.]

STARTING THE ENGINE? Does this only happen after you ran engine and shut off engine while the AC was on. Then restart engine with AC still on from before?

Expansion valve/orifice tube ( can remember which system) is plugging and not allowing system To equalize pressure on shut down. After seeing the quality of them go downhill, I shut of the AC about 2 minutes before engine off.

See this above the 110 temps most often, especially if you are
A tad high on charge.

 

[WarWagon]

Yes, starting after running before. The compressor manifold has been trouble on this truck since I got it. The 1995 will sometimes cycle the clutch after a hot startup.

 

[Will L.]

Too much oil in the system is more likely to plug up the expansion valve. With this ongoing problem I would be very tempted to R&R expansion valve and of course make sure you have a nice flat surfacefrom the compressor manifold / lines. Flush the system out (remove all the oil) start over with the exact amount of oil and refrigerant. I know you dont want to hear this, but when chasing a reoccuring problem, start with known good and go from there.

 

[WarWagon]

System worked fine with the old R-12 compressor level port design for 3 years. New compressor (o-tube, accumulator) went in this year due to a seal leak on the reman compressor. The stepped ports brought this old problem back. (Can't find a reman unit with the level ports anymore.) System was flushed and proper oil and freon put back in. The system flush was done several times in the past till I found the proper compressor. Hoses were repaired about 3 years ago. Suspect it is simply the manifold being warped.

I also switched over to the VOV for a big cooling difference. However either o-tubes were in use when this seal has blown out.

 

[GM Guy]

do you have pics of the differences? I need to go look at mine, not sure of what I got.

 

[Will L.]

Any good machine shops around you? Have a manifold cut from steel,w/ threaded outlets for the hoses. Get the hoses redone with jic or the like ends. Take the compressor to the machine shop as well for them to check a level deck. Yeah, I know $$$, but It would eliminate that issue permanently.

Is this a problem for others or just luck of the draw? All the ac I did was production r&r. No down time allowed, if it needed 3 parts, the whole system was r&r no questions. We had a better parts room than any dealer around!

 

[WarWagon]

This is a possible issue for systems that were factory R-12. Again the high side port is 1/8" lower than the low side port on R-134a designs. The R-12 compressors has level ports. You can see the difference.

New R-134a compressors are being used and work without leaking on the 1995.

A new set of 1994 R-134a hoses with the stepped manifold should solve the problem. If I really wanted to redo the hoses I would follow advice of others on here and drop a Sayden compressor on it and get rid of the power hungry and unreliable R-4. Adapter kit $69.00 and cost to re-do the hoses to change to a modern compressor...

I verified that it was the high side washer that leaked on the compressor manifold connection. The safety did not vent. The system lost 1/2 LB of R134a.

 

[WarWagon]

Although in the middle of winter elsewhere... Here our winter preparation is making repairs to the AC that has suffered all hot summer long and is still in use.

Posting up some pictures of the line set manifold differences between the R134A and R12 design. This has given me no end of trouble on the 1993 by blowing off 0.5 LBS of R-134A at the high side compressor connection after a heat soak hot start at times.

Old R-12 lines with level ports:




Simply weak bailing wire and duct tape adaption for the 134A stepped ports with the failure prone under extremes thick washers.




Murry replacement R-134A lines from a 1994. GM no longer has these including vintage GM parts. Possible to just replace the manifold at a AC hose shop. Cheaper for new lines at <$100.00

 

[WarWagon]

After doing this I noticed the belt starting to chirp under high load and then the high side relief valve vented.
Heat soak is causing extreme high side pressure on both the 1995 and 1993. The 1995 just has a working high side cut out switch...
I replaced the high side cut out switch. Quality is so poor they only have a 1 year warranty on AC switches at parts stores now.

 

[GM Guy]

what brand of switch? I thought delco's had a better warranty than that?

 

[WarWagon]

Murry O'Reilly brand. AC Delco is made in Communist China now too.

 

[Twisted Steel Performance]

I know this is a little old, but I saw you mentioned a adapter from R4 - sanden for PS compressors??? If there is such a thing, post the info, I'm changing out my AC now.....