Acid damage to compressor?

[shadow460]

This is the third compressor that's gone bad in my '98 Expedition. The one that was on it was bad when I got it. I took it to a mechanic to have a new one installed; they put a NAPA Cold Power and it lasted a little over two years.
I replaced it myself with a rebuilt Murray unit that lasted four months. Neither of us replaced the dryers although I did pull a vacuum for about 90 minutes and I weighed in exactly 62 ounces of R134a. I also have the "old" 134a in a recovery tank.
The first two compressors leaked around the shaft seals. The one I put on gets pressures of 45 and 165 which won't cool the vehicle.
I don't know if the compressor I put on failed from acid or if it wasn't rebuilt correctly. I know from experience how acid kills residential AC compressors: it destroys the electrical part inside the compressor. Well, here we don't have anything electric in the compressor at all to destroy.

My question is what exactly does acid do to a motor vehicle compressor? With no windings to attack (unless you drive a hybrid), what's left??

 

[stamp11127]

The acid will "eat" the aluminum parts of the system, send small particles through it that ends up in the accumulator.
Since you know more about a/c than the average person, what was wrong with the first compressor that required it to be replaced?
What is the ambient temp and static pressure?

 

[shadow460]

The one it had when I got it had a leak at the shaft seal. Eventually the Napa one started leaking at the same place. The Murray one I took off struggled a bit developing pressure.
There is no acid in the system. I used a QuickCheck 2000 acid test on the truck and on the recovery bottle. Both are clean.
I did something dumb, though. I didn't think to check the difference between the front and rear AC systems. The rear was blowing cold with the newest compressor and the front was blowing 80 degrees. The stupid knob had slipped out of position on the temperature control.
It still takes a bit to cool down even now if I've got both systems on max and all the interior vents open. If I just use the ones I need, it gets cold pretty fast.
I've seen acid eat up an aluminum condenser coil, but that was after a compressor burnout that sent a fresh dose of acid throughout the system. It was a central AC unit and the entire thing had to be replaced. Yuck.