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1974 Riviera A/C mystery

JasonKuehn on Fri June 22, 2012 3:40 PM User is offline

Year: 1974
Make: Buick
Model: Riviera
Engine Size: 455
Refrigerant Type: R-12
Ambient Temp: 75
Pressure Low: 30
Pressure High: 45-50
Country of Origin: United States

Hello all, this forum was recommended to me so I thought I'd give it a shot. This situation is really odd to me, but hopefully someone here can help solve it.

Bit of history: I have a 1974 Riviera, 100% original and only 6000 miles. It sat in a garage 17 years until I got it out and going again around 2000. Put a few hundred miles on it, everything was great, A/C worked fine. Then, I think in 2002, the A/C clutch burned up (made big time smoke when it happened since it had some kind of rubber cap around it). Not long after that, I put it back into storage since I was moving around a lot with work.

Fast forward to 2012. I got the car out of storage and running again. I replaced the A/C clutch, but no cold air. I figured the charge must have finally leaked somewhere. I pray it's not the compressor since 1, theyre expensive, and 2, I just spent time and money putting a clutch on it!

Get out my manifold gauges and I have good R12 charge! Low side is right around 30 where it should be, sight glass is clear. However, and this is the weird part, the HIGH side isn't doing squat. Maybe 40-50lbs max at high idle and a/c turned on full. The clutch is kicking in and I can see it turning. With the engine off, I can easily turn the compressor by hand in both directions with no noise or roughness.

I would think that if the compressor had went out and partially locked up maybe that could have burned the original clutch. However the original clutch was fairly rusty and the the flexy spring steel things were all broken so I figured that might have went out on its own. But why would the compressor turn freely now with no noise and a smooth feel if it was bad?

Anyone have ideas as to what might be causing this issue? I have a big stash of R12, but I really don't want to replace the compressor without being sure since I don't have the equipment to flush and evacuate it properly and it's probably going to cost at least $500 to have it done.

Dougflas on Fri June 22, 2012 7:56 PM User is offline

First, make sure the high side handwheels are closed. when you say the clutch turns, I hope you're talking about the smaller front hub of the clutch. A clear sight glass can mean 2 things: either a full charge or a completely empty system.

GM Tech on Fri June 22, 2012 11:38 PM User is offline

recover the charge - you probably have only 5% of factory spec in there.....

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

chris142 on Sun June 24, 2012 6:34 PM User is offline

My guess is that when the clutch burned up it damaged the front seal from the heat.

JasonKuehn on Tue June 26, 2012 11:20 AM User is offline

If it was empty of refrigerant why would I still have the factory spec of 30lbs at the condenser?

Just as an experiment, I tried adding more R-12. I got the low side up to about 75lbs, and the high went up to about 100. I was afraid to go any higher since this was double what it should be and it wasn't making much difference. The return line was cool to the touch, but air in the cabin didn't feel much different. I then let it back down to 30lbs where it should be. Interestingly, after letting the low back to 30, the high stayed around 100. I'll check it again later to see if this is still the case.

I'm thinking there is a blockage somewhere. Does that sound feasible?

Has anyone ever seen a bad compressor that made no noise and turned over smoothly and easily? (@dougflas, yes I'm referring to the part that is supposed to turn, not the fixed part)

Edited: Tue June 26, 2012 at 11:21 AM by JasonKuehn

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