Engine Size: 350
Refrigerant Type: R134
Ambient Temp: 85
I have gone thru at least three R4 compressors, at least one per season. It appears that freon again leaked out and there is oil residue on the body of the compressor. Same symptom as the last two. I splurged and purchased a good quality four season compressor thinking a better quality compressor will do the trick on the last go around. I noticed I had a missing bolt on the frame the supports the R4 thinking that possibly that the body was warping over time. But it appears there is something else going on here. I do not have a high pressure cut off switch on the high line. But I would think if high pressure is the issue it would trip the relief valve in back of the compressor.
88 Suburban with rear air. This is a R134 conversion with updated parallel flow condenser. Textbook conversion freon charge 134A 70-80% of R12 recommended load, blue orifice, flush, accumulater, and vacuum for and hour with no leaks...yada yada yada. Measure pressures were around 30 low and 200 high. I would get around 45 deg in highway...which was much better than now.
Any recommendations to make this bulletproof short of changing vehicles. I recently rehauled the drive train, so this workhorse has some life left.
See next post.
Edited: Wed September 23, 2009 at 12:54 AM by Cussboy
Below, here's what a well-known local mechanic (with weekly radio show) says about these rear AC systems. I myself have a '94 Suburban (since 2000) and have replaced the R4 compressor 3 times (OK, I'm in Arizona, 110K miles are ours, 70K before us). I never had a compressor seize on these, just belly-leak. Right now my rear expansion valve is stuck closed, so only my front AC works (cold) so I'm not doing anything about it, as my kids are older now and away at school (that may help my compressor life, actually). Previously, I had a 1988 Sub with rear AC, replaced its R4 once. This does make some sense to me, as these compressors seem to last longer on GM trucks that don't have rear AC.
MUST READ for those with rear A/C.If you are using your A/C and have rear air conditioning, NEVER shut the rear blower off and never run it on low speed.
If you get too cold, don't shut that rear blower off or put the fan speed on low, open a window and mix some warm air with the cold air inside. As a matter of fact, if I were King, I would eliminate low speed on all rear fans, during use of the air conditioning . . . and here's why.
The air conditioning compressor cannot handle liquid on the suction side. So the front AC unit dumps or sends it's refrigerant (or Freon) back to the compressor via a can called an accumulator where any liquid left falls to the bottom and the gas rises to the top and then is fed back to the compressor. This is important because the compressor cannot compress a liquid, only a gas.
The rear AC unit has no such can or accumulator so unless we turn the liquid to a vapor, (or evaporate) the Freon in the rear air conditioning unit by using the rear fan, all we end up feeding the air conditioning compressor from the back air conditioning unit is liquid Freon which wipes it out. The air conditioning compressor cannot handle sucking in a liquid and compressing it, it can only handle or compress a vapor. That's exactly why so many rear air conditioned vans, Suburbans, Explorers and other SUVs have major air conditioning problems year in and year out.
This isn't a new problem, however, it's been only recently that GM has determined that the absence of an accumulator for the rear air conditioning unit can and will cause these problems. They always thought folks would use the heck out of the rear air conditioning and never considered the drivers would run with the rear unit fan shut off.
So wives, tell your husband to stop running the air conditioning with the rear blower on off or on low. Tell him to run the fan on medium to high.
Edited: Wed September 23, 2009 at 12:54 AM by Cussboy
Sounds interesting but I seen systems with rear air run fine for several years. I not too familiar with the mechanics of an R4, but if a liquid is in the cylinder I would think there would more likely be a catastrophic failure of the pistons and rods since the pressure is created within the cylinder. I would also think that you would hear the compressor making noises under stress. Maybe someone can chime in on that.
Running the rear air at full blast with the windows rolled down seems counterproductive. The rear air running at full blast will give everyone a headache after some time.
In addition to the Suburban, I own a 2000 Expedition with rear air. The rear system is only used 2% of the time. I had the compressor go out in 2002 under warranty. It has been running strong for almost 7 years without a hitch. This unit has blasting 40 deg consistently with no recharge since then.
I do not recall ever having problems with the compressor when I purchase the vehicle back in '96 when it was with R12. The first R134 conversion was done around 2005, it was after the conversion that I begun to have chronic R4 problems.
I search and found several posts related to a severe reduction in service life of a R4 when a R134 conversion is done. There maybe something to that theory. If anyone else can chime in that would be great.
The next approach maybe to go with a R134 friendly compressor, but I think that will be a retrofit nightmare. Maybe I am jumping the gun here.
I just have a question, how can you tell when the compressor is getting liquid sucked into the low side? Is it when the pipe on the low side at compressor starts to freeze? I
also have a 1988 suburban with rear air. Just another thought, isn't that what the expnsion valve is for in the rear air to prevent liquid refridgerant from entering the
compressor. That is, if the valve is calibrated with the right amount of superheat.
Edited: Thu September 24, 2009 at 7:22 AM by squeege
That mechanic means that when liquid refrigerant gets through the rear expansion valve, that if the rear fan is not running to help evaporate that refrigerant to a gas, then some liquid refrigerant gets to the compressor, and is both incompressible and acts to strip oil from compressor surfaces. He was being semi-facetious about opening windows in the rear if too cold, the best way would be to mix in some rear heat with the rear AC flow to meet comfort standards. It sounds somewhat logical to me...
Yea, but how do you know when liquid refriderant is getting to the compressor? because all I have on my rear air is fan high, low and off for ac only. I've noticed that on 75
degree day that if i just use the front air, the compressor cycles more often. When I have rear fan on low it does not cycle as often and cools the way i want it to. I have set
the low cycle switch to 23-25. Before that I had it set to 19-20. And in the same situation the low side at the compressor to the y to the rear air would be frosty white and of
course the compressor would not cycle until 19-20 on low side. My question is at the time the pipe turns white does that mean that there is liquid refriderant in the line?
Edited: Thu September 24, 2009 at 3:40 PM by squeege
I believe the common denominator for my problems is using the R134A since head pressures run much higher than using R12. There is a lot of webinfo related to R134 conversion problems.....
I done some research and found a product called Freeze12, which is basically a blend R134 and HCFC 142. It mimics the properties of R12 and supposedly provides much better cooling power than 134. Also head pressures are much lower than 134. The other nice thing is that most oils can be used with this product. I am hoping this is the magic bullet.
Anyone on feedback on taking this approach? The seasonal change of the compressors is starting to become a nuisance.
I just spoke with a technical representative with Four Seasons and he mentioned that absolutely no way should this compressor leak with a R134 application.
He mentioned that it is possible that the compressor was not torque correctly which would result in warping the cast and the end result would be body o-ring leakage. I ran across a post which indicated that GM put a TSB related to compressor leaks due to improper mounting.
If anyone can share some info regarding this TSB that would be great.
Not dealing with R134a but we had a Isuzu Rodeo here a couple months ago that too either 6 or 7 compressors to get one that didn't have a case seal leak. We acquired them from many different vendors and Four Seasons was one of them.
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