A/C question

[Bigtime53]

I have had to change my a/c compressor now 3 times because of the rebuilt ones I have bought at the parts house. I finally found a new compressor and put it on and it is working. My question is each time I put a compressor on I had to ad oil to them which was 2-3 ounces each time so now I am thinking after 4 times I have to much oil in my a/c lines. My a/c cools ok until I drive about 5-6 miles then the air gets warmer. I put a therometer in the vent and upon startup it cools to 48 degress then after a while it goes to 68 degress and stays there. I am thinking there is to much oil in the system and that is the problem. So is that what is causing this or do I have a problem somewhere else? Thanks

 

[1987 GMC Jimmy]

Going by the book, you’re supposed to replace your accumulator and orifice tube and perform a flush each time you do that job. The purchase of those items is technically supposed to be proven when you claim the warranty on a compressor. Was a flush performed any of the times you replaced compressors? If something’s out of spec, whether it’s refrigerant or lubricant, A/C system performance will be impacted. The flush gives you a fresh start in that regard.

 

[Bigtime53]

I did change all of that the first time but not after that. The compressors [none of them] would last 100 miles cause they would leak all of the freon out from around the compressor clutch. They must of have a bad run on that part of the compressors cause I got 3 of them before I found the new ones offered and installed it. So I guess I need to vac the system and start over or do I need to replace the other parts to?

 

[1987 GMC Jimmy]

Yeah, that type of failure is not uncommon on rebuilt radial compressors. They don’t rebuild well at all. Accumulators and orifice tunes are so cheap, I’d replace them just to be in check with my warranty and know that everything was done right so I wouldn’t have to throw away all that freon again. If the parts store isn’t hassling you, I don’t think it would hurt anything if you didn’t replace, but an open system is not good for the desiccant in the accumulator anyway. And I’d really do that flush above all things. Bottom line, I think you could get away without a new o-tube and accumulator if you didn’t want to spend the extra $20, but if it were me, I would replace them to avoid anything that would make me have to do the job yet another time.

 

[hatzie]

Too much oil will coat the evaporator and condenser and cut down on your thermal transfer. Sounds like that's what you have there.

You really should flush the system to get rid of the chunks of old failed compressors and clear out the old mixture of R12 & R134a oil... then you should replace the o-rings, accumulator/dryer, and orifice valve.

There's a spec for a full system oil charge in the service manuals. I prefer to dump the wet unknown pedigree oil in a new compressor into a measuring device and re-fill with the same volume of dry known pedigree Ester oil with UV dye. Subtract what you use to re-fill the compressor from the total system oil fill listed in the service manuals. Put that remaining amount of oil you calculate and no more in the system with an oil injector after you vac it down.

 

[yevgenievich]

Should at least empty removed compressor, add measured amount of oil back and change orifice tube as it is a filter.

 

[hatzie]

Should at least empty removed compressor, add the measured amount of oil back and change orifice tube as it is a filter.

There are three problems with that approach;

1. The dryer desiccant is likely loaded with moisture.
2. There's still a mix of moisture laden Mineral and Ester oil insulating the condenser and evaporator, intermittently blocking the orifice valve, and slugging the compressor. The first two are just costing fuel mileage and making the cab uncomfortable. Slugging the compressor with oil will destroy it in short order.
3. The system is loaded with pieces of four failed compressors... Three replacements and the original unit.

The compressor Vaughn has installed on his truck right now will frag out just like the last four if this is not tended to properly... It may already be dying.

 

[yevgenievich]

That was the least needed to have a somewhat working system assuming correct oil already in the system. More or less an option if just changing compressors while dryer is new. Really just a note for someone else stumbling in to this thread who has just a leaky r4.

With so many failed compressors the whole system is unknown and as was already stated will need complete flush and orifice/dryer replacement. Did not see a need to type out what was already stated.

There are three problems with that approach;

1. The dryer desiccant is likely loaded with moisture.
2. There's still a mix of moisture laden Mineral and Ester oil insulating the condenser and evaporator, intermittently blocking the orifice valve, and slugging the compressor. The first two are just costing fuel mileage and making the cab uncomfortable. Slugging the compressor with oil will destroy it in short order.
3. The system is loaded with pieces of four failed compressors... Three replacements and the original unit.

The compressor Vaughn has installed on his truck right now will frag out just like the last four if this is not tended to properly... It may already be dying.

 

[hatzie]

Making the warranty valid on a replacement compressor depends on the install of a new dryer and the correct system oil charge being installed.
The accumulator dryer will have an unknown quantity of the system oil that's not in the compressor. The new one will not have any oil. This oil quantity is an unknown so, without flushing the rest of the system, you can't get a handle on how much oil is needed to make the system fully charged.

I would never trust that the previous owner didn't alter the oil charge level or more commonly double it during R12 to R134a conversion by adding ester oil when there was a full charge of mineral oil already present.

That aside. The only reason to replace an AC compressor is when it failed or is faililng in service.
There will usually be finely ground bits and pieces of the vanes or pistons/rings etc suspended in the refrigerant oil in the condenser, accumulator/dryer, and evaporator. You wouldn't re-use the engine oil or transmission fluid you drained from the old unit. BRRR. Nasty thought that one... Nor would you install a new engine or transmission without flushing out or even replacing the aux oil or transmission fluid cooler and lines. An AC compressor is no different.

 

[Bigtime53]

Ok guys thanks for all of the input. This next tuesday or wednesday when I am off I have a friend who is a gm ase certified mechanic and will have him flush the system and start over with the new dryer etc. I am not going to change the new compressor as that is a expense that I do not want to do again. This time the new compressor does not have 50-60 miles on it as I was hoping it would cool like it is supposed to until I thought about all of the oil in the system as I explained in my original post. If it ends up still not doing what it is supposed to I will have to bite the bullit and start all over again with everything new.

 

[1987 GMC Jimmy]

I think the compressor will live and do what it’s supposed to when all is said and done. If it’s not grumbling, I think that’s also a good sign. Mine did it at the end of its life, but some of them do it forever and keep on going. Like I said they’re no good for rebuilding, but the original Harrison R4 on my Jimmy lasted until 2016 with 183,000 miles. It just puked all the refrigerant out of the front while it was sitting. I don’t hear about these seizing and causing a big mess like some others do. It probably would have gone longer if it hadn’t sat so much over the years. They’re not weenie compressors, but it takes a somewhat fragile balance of refrigerant and oil to make them work right and last.

 

[yevgenievich]

Off topic a bit, but do you happen to know if gm changed to metric threads on the couplings for ac system in the squares and when if they did. Edit: looks like as long as it is using numbered designations it should be same.

Making the warranty valid on a replacement compressor depends on the install of a new dryer and the correct system oil charge being installed.
The accumulator dryer will have an unknown quantity of the system oil that's not in the compressor. The new one will not have any oil. This oil quantity is an unknown so, without flushing the rest of the system, you can't get a handle on how much oil is needed to make the system fully charged.

I would never trust that the previous owner didn't alter the oil charge level or more commonly double it during R12 to R134a conversion by adding ester oil when there was a full charge of mineral oil already present.

That aside. The only reason to replace an AC compressor is when it failed or is faililng in service.
There will usually be finely ground bits and pieces of the vanes or pistons/rings etc suspended in the refrigerant oil in the condenser, accumulator/dryer, and evaporator. You wouldn't re-use the engine oil or transmission fluid you drained from the old unit. BRRR. Nasty thought that one... Nor would you install a new engine or transmission without flushing out or even replacing the aux oil or transmission fluid cooler and lines. An AC compressor is no different.