Converted A/C system needs new compressor - which kind?

Mid-80s chevy suburban, 6.2L diesel, with the rear A/C blower, too. System was converted from R-12 to 134a years ago. Few years ago started to leak slowly-- would put in a fresh can of fancy synthetic 134a at the beginning of each summer and it would blow nice and cool all summer, and wouldn’t need it again until around the same time the next year. This year, put in two and a half of the giant cans and still couldn’t get cold air or the compressor to cycle (it engages the clutch once enough 134a is in, reads correct on the gauge, but never is able to get the pressure down to the shutoff value). Air blowing inside still a few degrees above ambient. When I gave up and shut off the engine, could hear a distinct loud hiss from the compressor. Hard to tell for sure, but sounds like between the pulley and the housing, so probably at the bearing? The fancy 134a has UV dye, but can’t find my backlight to confirm. If it’s coming out as a gas, would there even be dye to see? Pressure gauge read zero the next day, and I’m not wasting any more 134a without more info.

Couple questions:

This is the compressor gone bad, right? I’ve read you can’t go on hissing alone because some systems are still moving the gasses around inside after shutting down, though this certainly sounds like a leak, and the pressure is gone the next day. Don’t want to toss a good compressor on the off chancier wrong, so anything else I can do to verify?

So, new compressor-- which one? This, I believe, is the original R-12 compressor, just flushed and lubed for 134a during conversion (I assume, wasn’t there myself, how to know?) If that’s the case, then the big issue is: do I find another R-12 compressor and install that? Do I have to flush or lube it or whatever beforehand? Or do they make a 134a compressor that fits this older truck? Wouldn’t a compressor designed for 134a run cooler and more efficiently?

NAPA was no help, they list like fifty compressors for this truck, most of them look totally different.

When you buy a new compressor these days, they are NOT pre-oiled and you get to select.
I just looked up a new one for an 85 diesel suburban on Auto Zone and I also see three different styles of compressors…A6 - HR6 - & DR6. Buy the one that looks like yours
All of which will be compatible with either refrigerant…use the correct oil and you’re good to go.


Maybe i’ll try AutoZone then. PepBoys said they didn’t carry and couldn’t even order a compressor for this truck.

I am curious, though: if all compressors perform the same on r-12 versus 134a, what part of the system doesn’t? I keep hearing converted 134a systems don’t run nearly as cold as the new cars designed for it from the start.

134 is a different gas and behaves differently, operating pressures are different. It’s not as efficient a refrigerant. Older condensers don’t always dump off enough heat for efficient cooling, 134 doesn’t circulate the mineral oil that was in R-12 systems, so you end up adding ester oil, resulting in an over-oiled system that can affect cooling. R-134 will leak through a hose that will hold R-12 so you may have leaks you didn’t have before.

After converting to 134 for a couple of years I gave up on it and just went back to servicing/repairing with R-12.