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I think I need a new compressor -- R4-OR vs R4-SW

kelobro on Wed September 03, 2008 4:31 AM User is offline

Year: 1991
Make: Chevy
Model: Caprice
Engine Size: 305
Refrigerant Type: R134
Country of Origin: United States

My son ran the AC with the aftermarket electric fan off (mech fan was removed). Something in the compressor blew, A puff of R134 and oil came out of the compressor. It doesn't sound right when running, it has a hissing noise now. To my surprise, it still had refrigerant in it. I assumed the sealing washers blew. I replaced them but the system won't hold a vacuum. I assume the compressor must be replaced at this point.

The original compressor was a R4-OR (used o-rings, not sealing washers). The one I used when I converted to 134 uses sealing washers (green and black). I would prefer the o-rings, since it is difficult to get sealing washers locally. Is there any reason I cannot go back to the R4-OR type compressor?


(former Arizonan, born in Chandler)

iceman2555 on Wed September 03, 2008 8:37 AM User is offlineView users profile

The major reason for not returning to the 'older' oring design is simply that they are no longer produced. It is doubtful that the sealing washers are the source of the leak. Check the rear head of the compressor for a small brass 'plug'...this is probably the source of the leak.
It is possible that the sealing washer is leaking, the high pressure discharge port, esp if the short insert was not installed in the hose manifold.
Test the areas with a known good leak detector...not simply seeking a 'hissing' sound. A leak this size could be noted with the age proven technique of 'soap bubbles'...if nothing else is available.
The noise is probably originating from operation of the system with a system undercharge. The 'puff of 134a and smoke' was a release of refrigerant due to excessive high side pressures, the result of an inoperative electric fan. This lack of refrigerant results in lack of lubricant flow to the compressor.
The system should be recovered,evac'd and recharged. Adding a small amount of lubricant should be acceptable. There is normally very little loss of lube in this 'blow off' process. 1-2 oz should be sufficient. Insure that the system is properly recharged. The noise issue may be abated somewhat by this procedure.
The pressure relief valve, the brass fitting, may have to be replaced also.
This is one of the serious downsides of replacing mechanical fans with electrical units. The fans system should have been installed with some type of activation geared toward A/C compressor activation and the very minimum a switch located in the high side to activate the fans at a given pressure.
Reliance on 'turning the fans on' is simply not an acceptable is to easy to forget. Were the fans recently installed....operation of a engine without fan operation may also result in serious engine damage. Interested in how the fans were they are many were installed....and what sizes.
Many are installing these 'aftermarket cooling wonders' in a mistaken idea that increased gas mileage will occur. The 'OE' mechanical fan is hard to beat.....if operating correctly....good cooling...reliable cooling.....and not a serious deterrent to gas consumption.
Good luck!!!

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

mk378 on Wed September 03, 2008 9:25 AM User is offline

The relief valve may or may not reseal fully after it opens. Check for slow leaks there as well as fast ones. Find the leak for sure, this will be easier testing under pressure instead of vacuum. The relief valve is a seperately replaceable part. If you haven't already, try evacuating and recharging fully and see if it works OK with a full charge before condemning the compressor. You may need to add some oil but how much would be just a guess.

No matter what you end up doing with the compressor, add a high pressure cutoff switch so it won't happen again. You could also fit a combo HPCO/fan switch to automatically control the fans.

retrofit on Thu September 04, 2008 1:04 AM User is offline

GM says that R4 compressors made between 1-1-1990 and 6-18-1993 should not be used in R134a systems so watch out for those if buying used or rebuilt compressor. Sealing washers were use on some GM compressors starting in 1992 and on all by 1994 so check the date code.

Edited: Thu September 04, 2008 at 1:06 AM by retrofit

kelobro on Thu September 04, 2008 1:36 AM User is offline

The electric fan was originally tied to the compressor clutch. I disconnected that wire because I was trying to get home on marginal battery power and the 100 amp alternator wasn't getting the job done. I have since replaced the 100 amp alternator with a 140 amp unit. I REALLY like the idea of hooking this wire to a high pressure switch. As it is currently configured, The fan runs all the time in the summer because we are always using the A/C. There isn't a good reason for the fan to run when the car is traveling at 50+ mph. I really need a moderately high pressure switch to turn the fan on, then a high pressure switch to shut down the compressor to protect it.

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