A/C Compressor Differences?

[Mattheww044]

Hey guys, I have a 91 5MT SS. We tried doing the R12 to R134A conversion, but my compressor wouldnt "engage", so I went to the junkyard and got a "new" one. This one was out of a 91-94. Only after I finished installing it did I realize that the electrical connectors are different. Mine had a longer clip, with 3 wire "ports". Only one of them is being used with the wire that goes inside the compressor. The other 2 were "looped together" with a short wire, the replacement compressor only had 1 wire with 1 wire terminal on the clip. So I figured what the hell, and spliced my stock connector to the replacement compressor. Now the compressor wont spin at all. Obviously the belt side will, but with the car on max ac and all, the front part will not spin. I'm not quite sure if I need to change the wiring around on the clip, or get another compressor off of a car with the same clip or what. Has anyone else run into the same problem? The old one would kick on (front part spinning), but not actually engage and blow cold air. Any help is appreciated
Thanks

[Mattheww044]

The Yellow wire with the green stripe is used,
the brown/ red is not
the red/ yellow is not

But, its still hooked up exactly the same as it was before.... i just spliced the only wire from the new compressor to the original connector, and the wires still hook up the same. Did i just get unlucky and get a bad compressor or is something else going on?

[vrg3]

You got the wiring fine.

You don't say anything about how you charged the air conditioning system. Or, rather, starting to charge it. The system needs to reach a certain level of pressure before the pressure switch allows the compressor to turn on. You usually need the compressor to be on to fully charge the system, but you need to put somewhere between 6 and 12 ounces of R-134a in first.

If you already did that, then my suspicion is that you did indeed get unlucky and end up with a bad compressor clutch. You can test it -- unplug the connector, start the engine, and try connecting the wire going to the compressor clutch to +12v; it should engage. Don't do this if you don't have R-134a and PAG or ester oil in the A/C system yet, though -- the compressor needs oil to run correctly, and needs refrigerant to carry that oil.

[Mattheww044]

O wow, I have not started charging the system, I thought it would kick on anyways, but just not do anything. I feel like an idiot now, but since this is my first experience whatsoever with A/C systems things like this are bounf to happen. So how exactly do you put the oil in? same as the refriedgerant? And the oil needs to be first correct?

[vrg3]

You should read up on this before continuing. I'll get you started:

The A/C compressors is lubricated from the inside, where the refrigerant is pumped through. The oil is carried through the whole system by the refrigerant -- the compressor spits it out with the refrigerant going to the condenser, and it gets carried through the condenser, receiver/drier, expansion valve, evaporator, and all the way back to the suction port of the compressor by the refrigerant.

R12 systems use mineral oil, but that type of oil doesn't mix with R134a. There are two types of synthetic oils that work with R134a -- PAG oils and POE or ester oils. There are differing schools of thought on whether or not you should flush out the old mineral oil with a solvent when you do a retrofit. Supposedly, POE oil is somehow more compatible with the old mineral oil and so are sometimes recommended when doing retrofits without flushing (most cheap retrofit kits include ester oil). POE oil isn't quite as good a lubricant, though, and no OEMs use ester oil for original equipment or for retrofits, though, as far as I know. I personally feel the way to go is to flush and used PAG oil.

There are different ways to get the oil in, and differing opinions on which way is best. You can buy cans of refrigerant that also have oil in them. Cheap retrofit kits usually include these "oil charge" cans (again, with POE oil in them). The idea is that you shake 'em up and use them to charge the system, and that gets oil in the system too. Another approach is to get the oil in a can or bottle and slowly pour it into the suction port of the compressor as you turn the compressor clutch by hand. Finally, you can pour it directly into various parts of the system -- the compressor as described, the condenser, the receiver/drier, the evaporator... What I generally do is pour half of it into the receiver/drier and the other half into the compressor using the above method. That way it's not too hard but there's some oil already in the lines so the compressor won't run dry. My experience oil charge cans is that it's hard to get the oil to really flow into the system past all the valves and fittings. It may have worked better in the R12 days but R134a just doesn't mix that well even with PAG or POE oil.

Other things worth noting:

Both PAG and POE oils are hygroscopic and so you want to limit the amount of time they spend exposed to the atmosphere. There are new "dual-capped" PAG oils that supposedly aren't hygroscopic, but I don't know much about them.

You should use a new receiver/drier. It contains dessicant that becomes full of water if it's left exposed to the atmosphere. Also, oil receiver/driers used dessicant that isn't compatible with R134a. Again, minimize the amount of time between installing it and charging the system.

You should evacuate the system before charging it. Use a vacuum pump to pull a deep vacuum on the system to make sure there's no air in it and the boil off any residual moisture.

The A/C system isn't very complicated, but you should do some more research before diving into it.

[Legacy777]

I've got a thread in the misc forum about retrofitting an R12 to R134a system. It goes into some more detail about what specifically needs to be done. I'd suggest reading over it. After some experience, the only thing I'd change is I'd suggest using PAG oil rather than esther oil. The esther oil just doesn't lubricate as well.

http://bbs.legacycentral.org/viewtopic.php?f=11&t=1083

The AC system, while not overly complicated in its workings does have some items that need to be taken care of for it to work properly.

[Mattheww044]

wow, thanks for all the info guys. Very helpful