95 AC compressor replacement

[PAman]

I'm trying to replace a '95 HD6 compressor, but haven't found one from a salvage yard yet. Beside hoses, does anyone know of any other differences between this and a '96 or later V5? The '96 takes the same evap, condensor and accumulator, so is the difference in the pulley dia, offset or distance from mount? Also, the VIN K is actually a '97, but I don't remember changing anything relating to the compressor mounting. I can deal with electrical connector differences, if needed. I was looking at replacing hoses anyway, but I was hoping this and a possible belt change would at least get the car back on the road.

[HotZ28]

Three common methods exist for throttling back the A/C when (or if) the car gets cold enough. The simplest method is to have a thermometer at the evaporator (air) outlet and shut off the compressor when it drops to approximately 32F. The last two are much more common and both look at the suction (low side) pressure to decide when to stop/slow down cooling. As the evaporator cools down, the suction pressure also drops. Older cars (such as using the infamous GM R4 & R6 compressor), have a switch in the low pressure side of the system which opens at about 24 PSIG, cutting off the compressor. The evaporator warms up, and when the pressure reaches around 40 PSIG, the switch closes again, restarting the compressor. This method causes a lot of wear and tear on the compressor clutch. Newer cars, have variable displacement compressors, which run continuously instead of cycling off and on. They have a swash plate instead of a crank shaft to anchor the pistons. The stroke of the pistons in this type of compressor may be varied from maximum to almost zero, by varying the angle of the swash plate. A GM V5 is a common example of this type of compressor. These compressors usually have an internal mechanical arrangement to control the swash plate based on the suction (low side) pressure. They are usually set for about 28 PSIG. When the car is hot, the suction pressure will be much higher than 28 PSIG, so the compressor operates at full stroke. When the car cools down, the suction pressure drops down through 28 PSIG, and the swash plate moves, reducing the stroke of the pistons, and lowering the capacity of the A/C, and the suction pressure will stop dropping, and stay at around 28 PSIG. The compressor will continue to reduce displacement by maintaining the suction line at 28 PSIG if the car cools down too much. If the sun comes out, and the car begins to heat up, the suction pressure will rise above 28 PSIG, and the compressor will increase it’s displacement to bring the pressure back
down to 28 PSIG.

With all that said, if you put a V5 on a system designed for the HD6, you would have to eliminate the low pressure cycling switch. Also considering the other modifications required, it might be cost prohibitive to change over, when you can buy a rebuilt HD6 for $200.00 at O'Reilly Auto Parts with a warranty.

[PAman]

Thanks for the education. But it raises a few more questions. Based on what you stated, is the stroke control internal to the variable displacement compressor? If so, why wouldn't you want to allow it to disengage the clutch below 22-25 psi as a precaution anyway? Based on the 28psi threshold you stated for the variable disp. unit, the system may not reach the 22-25psi switch setting of the HD6 system very often. And if it did, why not cycle the clutch? If that's a problem, why not jumper the the LP switch connector so the PCM won't allow that input to disengage the clutch? Also, being a VIN K, that compressor runs about $270 + shipping from O'Reilly, and the best price I can find is only slightly less. I don't need to put that much into the car, considering I need the AC for, at most, only a few weeks here in PA. (Well, more this summer, but this one is atypical!) As you can see, my primary concern will be mechanical installation.
Your thoughts?
Thanks again.

[PAman]

A quick correction and clarification to my reply above. The 4th sentence should read:
"If so, why wouldn't you want to allow the system to disengage the clutch below 22-25 psi as a precaution anyway?"

[HotZ28]

When the car cools down, the suction pressure drops down through 28 PSIG, and the swash plate moves, reducing the stroke of the pistons, and lowering the capacity of the A/C, and the suction pressure will stop dropping, and stay at around 28 PSIG.

These compressors usually have an internal mechanical arrangement to control the swash plate based on the suction (low side) pressure.

I would think that under normal conditions, the (V5) would not go down to 22-24 psi without changing the displacement; therefore, you may be able to leave the cycling switch in place. If it does cycle off, you could jump it out as you suggested. In doing a cost benefit analysis of the change over, I assumed that a used compressor, hoses, pulley or belt would cost more than a rebuilt HD6. I would love for some one to try the change over and post here with the results so that others may consider this as an option.

It would be "cool" if it works!!

[PAman]

The quick update is, no update. I've been away for 3 weeks and haven't been able to get to it...maybe this weekend.

[HotZ28]

Thanks for the feedback anyway. Keep us informed!