GM A/C compressors: What to use for proper oils for R12 and R134A

[GM Guy]

Hey all,

It is going to be 100 degrees today, so its a/c time!

we are working on various GM systems, so I figured I would start a rather generic thread, and we can hopefully cover what to use for oil in each system depending on what refrigerant is being used, such as what oil to use in the R4 with R12, or R134A

so, right now we pulled vac on the 98 K2500HD of the folks'. we are using R134A, what it came with from factory. what model (and brand) is this, and what oils can be used? dad is prepared to use this synthetic universal oil he has, and I fear this compressor is picky, and he will ruin it. so, what to run?

the next compressor is the R4 in the 1995 GMC. to my knowledge, we have only added refrigerant (R134A, what is called for from factory) and dad "might" have put some random R134A compatible oil in the hose, just enough to fill the hose, then rammed it on through with a refrigerant charge.

what does the R4 take? will also be working on the 1993 Chevy, and likely converting it to 134A. would anything be harmed converting a R12 running R4 to R134A?

how old of GM truck has the good ol A6? will any 6.2Ls have it? it is rather bulletproof and can take about anything for oil, as long as the oil is compatable with the refrigerant?

I guess we need a list of what all was used on diesel GM trucks and what year range they came on.

 

[THEFERMANATOR]

R-12 systems all use mineral based oils. R4 compressors that came factory with R-134A use PAG 150 oil. Converted systems(R-12 to R-134) are best to use ester based oils as PAG has had some interactions when mixed with mineral based oil. The HT6 used from 96-02 for diesels and 96-99 half ton gassers, and to 00 for 5.7L and 7.4L engines as well as some RV applications speced out PAG 150 from the factory, but GM has changed and started using there own proprietary blend that is roughly PAG 120. Many replacement compressors for the infamous HT6 belly leaker now use PAG 46 or PAG 80 as the thinner viscosity is said to help the compressors live longer(but not run as quiet). Which oil to use can be tricky, but be VERY CAREFUL of using generic synthetic oils as most are ester based. As be careful with your oil charge as even an once over filled on oil will significantly reduce A/C performance.

 

[GM Guy]

thanks for the input ferm!

so in 95 systems, use PAG 150 only for max lubrication?

also, isnt it better to be a little over lubed and lose performance, rather than be under lubed and shell the compressor?

what all can go wrong with the HT6? we didnt figure out till 2 cans later that the high pressure connector leaks. does a guy just change the core, or is it best to change the whole fitting?

 

[WarWagon]

1995 high pressure service valves have a rubber half ball over then that can't be changed. Some factory 1995 hoses on gassers have to be replaced to fix the valve as it is one piece. Replacements are serviceable. Usually it's only the valve core that gets trash in it or cooked off so if it doesn't have the rubber in the way change just the core.

R4 compressors do not like ester oil! I have read this somewhere recently and blown my own up on ester in the past. (New AC delco compressor on a Yukon lasted only 14 months.) They get noisy and dump metal in the system with that oil in use out here.

Wrong oil used means you flush the system, replace the accumulator and add 8 oz oil, 11oz with rear air. (Same for leaks that have oil stains with unknown amounts of oil missing. THEFERMANATOR may have a way to tell how much oil is in a system?)

It is better to slightly overcharge the system with R134a than it is to put extra oil in it. the factory charge already has a leakage reserve in it. The accumulator holds 1/2 LB and figure it already has some used for the leakage reserve. Low on freon leaves even the extra oil in the evaporator and the compressor burns up anyway. I don't recommend doing either - rather evac and recharge the system every spring to make sure the proper amount of R134a is in the system. When the system blows colder than usual it is low on freon and the R4 compressor failure is not far behind.

1998 6.2's Suburban used the A6. Never had any trouble with the AC and R12 on that system in 5 years.

 

[THEFERMANATOR]

Best way to tell how much oil is in a system is to drain the old compressor when you change it. The evap should hold 2 ounces, the condenser 2 ounces, accumulator 1 1/2 ounces, compressor should have roughly 1-2 ounces in it, and the lines will hold about 1-2 ounces. I always prefer to err on the side of safety and run slightly less charge as it only takes a small amount of liquid refrigerant to hit the compressor and bend the reed valves. An ounce or 2 over on the oil VS the opposite is better. And when you start messing with the newer PAG 46 you will want to run a little more oil as it's lower viscosity messes with the pressures and you will either have to run more oil or more charge to keep the system running. And as for the leaking high side ports, use only the GM ones. I have bought them from NAPA, CARQUEST, AZ, and NONE of them hold up like the GM ones do. Also I hardly ever hook up the high side gauges as it almost always leaves you with a leaking high side pressure port when you remove the coupler.

 

[GM Guy]

so now a new question, dad saw fit to put his super universal ester oil in both his 98 K2500HD, and now my sister's 00 pontiac bonneville. any issues in doing this, or is compressor failure (to which he will no doubt blame on the high miles, not his adding possibly the wrong oil) in the near future?

we have put a can a year in my 95 GMC since I got it (2011) so it has had 2, awaiting 3 cans. I am prying for details if he had put any oil into it, I am hoping not. if he did put some ester oil in, how harmful is it, and should it be flushed? if so, how harmful are the flushing agents to component life?

dad has hated R134a since it came out, and he can get away with his mixing and matching of stuff on the old R12 systems (propane has been used, and any oil he can find) but his mixing and matching of stuff with the R134a is playing with fire.

he did pick up a GM R134a charging/ recovery machine at auction I need to try to buy off of him, maybe I will do my own.

 

[THEFERMANATOR]

R12 and mineral was pretty forgiving, but R-134A is not so forgiving. Chances are the compressors will start to degrade as ESTER does not have the sheer strength to it that PAG does since PAG is a true synthetic oil that doesn't require additives(that break down over time) to get to a certain viscosity. Since the oil was already mixed in I wouldn't worry about it to much now as there isn't much you can really do about it(flushing isn't all that effective unless you have a circulation flusher that uses liquid R-134A and filters to catch the debris).