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Rebuilt compressors

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  • Rebuilt compressors

    A few years ago I needed to replace a locked up A-6 on one of my trucks. I could get a O really?'s rebuild for under $150. Since then it lasted two years and then it would get hard to turn sometimes. This would cause the clutch or belt to slip, but if you shut the system down and re started it would continue. Finely it took out the clutch and the whole unit was replaced with a used compressor from the Northwest (Oregon) which likely saw little use.
    Today I opened up the old compressor to see what went wrong.
    With the guts out of the case, the 1st thing I noticed was when you tried to turn the wobble plate one piston remained stationary while the other two moved freely. So one piston was tight in the bore, it would move with more force applied to the shaft, but it was much tighter in the bore. The next thing I noticed was a fair bit of end play in the shaft. when the shaft was turned and the stiff piston not moving in the bore, the shaft would move fore and aft.
    The A-6 is supposed to assembled with selective fit parts, a .0005" preload on thrust bearing Having a zero end play is important for shaft seal life.
    Likewise the ball seats that ride on the wobble plate are also a selective fit. It is obvious that this compressor was assembled with what ever parts were to hand, and no fitting was done.
    I haven't pulled the halves of the guts apart to look at the piston and rings, but starting with such a mis-match of parts I don't know if I can find what I need to assemble correctly.
    Unlike most compressor failures, this one wasn't due to low oil level. I suspect the tight piston would get tighter as the system heated up. I have another compressor that suffered a thrust-bearing failure. May be there will be enough parts to make one good one. If not I'll keep it and the other one for a parts stash.

  • #2
    Since it looks like I am going to be building my own from this point forward I snagged a Kent Moore holding fixture and an O ring installer. I'm sure most dealers have long ago thrown these tools out.
    It will make my life easier, rather than trying to come up with a makeshift way of holding the rotating body halves.

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    • #3
      Ok got back to the compressor, I notice the two halves of the compressor were not butted tight together all the way around, it was tight on one side and a small gap 180 deg from there, WTF? Ok I'll split the halves, Humm, halves are not coming apart, why is that? Well they epoxied the transfer tube in place and that was the problem! Got the pistons out and put the two haves back together in the Kent Moore fixture and torqued the nuts, to check end play. I could fit a .010" feeler gauge between the thrust washer and case! Spec is .0005" INTERFEARNCE fit! The thrust washers ride on the outer edge on the wobble plate side and on the inner edge on the case side. All showed wear from the loose fit. I reversed the positions of all 4 thrust washers, so they were no longer riding on the worn surface and re-assembled, installed in fixture and checked the end play. While I can detect no endplay and can't fit a feeler gauge between the washer and case anymore, I think I am at around 0 clearance and no pre-load. Not ideal, but likely as good as I am going to be able to get.
      With the main shaft and wobble plate as good as I am going to be able to get, the next thing is to fit pistons and ball shoes. Again, I don't have a lot of parts to choose from to make it as tight as it should be, but I'm hopeful I can make it better than it was! The bores all look good and the valve plates are fine,

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      • #4
        Got the rotating parts back together. Generally I'm happy with it, No end play on the shaft and 2 of the three pistons with a little clearance and one with the desired no-play. Should work and may be a little noisy due to the end play on the piston shoes. If I had a supply of shoes I would look to make it tighter. Pistons all have nylon rings, which I am no crazy about but all that's left is to paint the case and assemble the guts into the case, and fit a new clutch.

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