R4 Compressor Troubles

[1987 GMC Jimmy]

Hey, all. I just drove from Wesson to NOLA (2 hrs) without air conditioning. It's 81 here in the Crescent City today so it wasn't unbearable by any stretch, but it would have been more enjoyable with cold air. My system is fully charged with no leaks, but my clutch does nothing. The compressor worked great the last time it did work and no groaning or grinding, but it's been a couple weeks since I had cold air. The low pressure switch was replaced at the end of last summer, and the belt is in good shape. I'm guessing I need to jump the compressor to see if I can engage the clutch and/or probe the female end of the two prong connector to see if it's getting power. The A/C stuff goes through a switch mounted on the Saginaw box, which I assume has to do something with idling up the car when the compressor's on and/or idling up when the steering wheel goes to full lock left or right. It's a pressure type switch. Do I need to probe for continuity and resistance within the switch, and does anyone have an idea of what values to expect? Could the fan selector switch do this because I had a defective one before that made the clutch engage as soon as I turned the key. And finally, should the diode on the compressor connector be of any concern? Any advice, experiences, pictures, or diagrams/charts would be received with the utmost gratitude. Just to add, I don't think it's mechanical in terms of clutch seizure, but I guess the clutch could have just died on it?

 

[yevgenievich]

Start with checking for 12v on both sides of the low pressure switch. If low pressure is tripped, need to check the system pressure

 

[1987 GMC Jimmy]

Start with checking for 12v on both sides of the low pressure switch. If low pressure is tripped, need to check the system pressure

Would a potential low pressure reading signify a leak? I did check for leaks and found none minus the evaporator since it's in the case, and I didn't have time. I put one of those crummy little R134a charge kits on it, and the little gauge on it said it was fully charged. I know that's the not the same as a legit set of manifold gauges hooked up to it, but I was just trying to supplement the info.

 

[yevgenievich]

Need to jump the clutch when checking pressure. If it is showing 20-40psi on the cold side with compressor turned off, then likely there is a leak.

 

[1987 GMC Jimmy]

Need to jump the clutch when checking pressure. If it is showing 20-40psi on the cold side with compressor turned off, then likely there is a leak.

At the low pressure switch connector, I got 13.6V on one side and 0V on the other.

Update: No continuity at low pressure switch. Damn thing lasted about 8-9 months. It's the Santech switch that Autozone sells. I'll replace it, and it should be good to go. I didn't know it'd be that simple. I guess I had too much faith since this was a fairly new part, and it worked before.

 

[1987 GMC Jimmy]

Well, I don't get this at all. I've got other low pressure switches that show continuity with a tester, but this particular one doesn't. I swapped it under warranty and nothing. I jumped the compressor at the low pressure switch connector, and it works fine... I guess I need to borrow a set of gauges and see what the problem is.

 

[yevgenievich]

Sounds like a leak. Put a gauge on it while the compressor is jumped with 12v. If pressure goes below 20psi or so then likely low on freon. Autozone rents gauges.

 

[CorvairGeek]

Unfortunately, a fairly rapid refrigerant loss out the shaft seal or a o-ring body leak on the R4 are all too common. The good news is that the replacement double lip, shaft seal does a better job than the original single lip or ceramic (pre mid '84) seals ever did.
I personally think a body o-ring leak on the R4 is fatal. Seen re-builds that work fine (which has always been the bigger problem) dump the charge out the body without warning. The thin steel shell of the R4 was too much of a crap design, IMHO.

 

[1987 GMC Jimmy]

Unfortunately, a fairly rapid refrigerant loss out the shaft seal or a o-ring body leak on the R4 are all too common. The good news is that the replacement double lip, shaft seal does a better job than the original single lip or ceramic (pre mid '84) seals ever did.
I personally think a body o-ring leak on the R4 is fatal. Seen re-builds that work fine (which has always been the bigger problem) dump the charge out the body without warning. The thin steel shell of the R4 was too much of a crap design, IMHO.

I looked in every crevice and corner of the compressor, and it was dry as a bone in terms of UV dripping or streaking. Would this manifest itself inside the compressor, or should I be able to look down between the pulley and the compressor body and see the leak because there's absolutely nothing there.

 

[CorvairGeek]

I've found the sudden body leaks around the perimeter to be very obvious and wet, just like you were looking for. The main shaft seal leaks can be sudden without much to make them obvious, or they can be oily to very oily and seem to hold refrigerant for years too. Even GM said in the shop manuals that an 'oil line on the hood does not indicate the evidence of a refrigerant leak'. I've always thought that was more a line deny warranty coverage, but it was in the manuals, at least through '84 with the ceramic seal. Certainly was the case with my Caprice.

The first step is to bypass the low pressure cycling switch and see if you have cooling and what your pressures are. Carefully inspect the o-rings on the switch and low/high pressure ports too.

 

[1987 GMC Jimmy]

I've found the sudden body leaks around the perimeter to be very obvious and wet, just like you were looking for. The main shaft seal leaks can be sudden without much to make them obvious, or they can be oily to very oily and seem to hold refrigerant for years too. Even GM said in the shop manuals that an 'oil line on the hood does not indicate the evidence of a refrigerant leak'. I've always thought that was more a line deny warranty coverage, but it was in the manuals, at least through '84 with the ceramic seal. Certainly was the case with my Caprice.

The first step is to bypass the low pressure cycling switch and see if you have cooling and what your pressures are. Carefully inspect the o-rings on the switch and low/high pressure ports too.

I'll have to try and do this over the weekend. I just ran out of time. Both ports are good and so is where the switch goes in. I've looked everywhere under the hood, and it's all dry as a bone. Literally the only place in the whole system I haven't looked is the evaporator core, but I'll put some gauges on and investigate further.