A/C Compressor Heat Switch?

[Alger R.]

I have another question regarding my 75 A-6 A/C Compressor. The back Plate does not have provisions for the small "Heat Switch Terminal " I have seen Compressors with a cast circular provision with a small "peg" for a Switch but not necessarily for a 75. Mine does not have this but yet I believe it to be the original compressor. The Assembly manual shows a wire leading to the back plate but I question if this is correct or not. Any help would be appreciated. Thanks, AL

[Edward J.]

Re: A/C Compressor Heat Switch?

Alger, does your car have the big valve next to the a/c box(POA valve)?your year car may have had the change over to the C.C.O.T. system, which did away with alot parts , -themo limiter switch,expansion valve,switch on rear of compressor, POA valve.

[Jack H.]

Re: A/C Compressor Heat Switch?

If memory serves, 1972 was the first year A6 compressors incorporated the 'super heat' switch feature. And, from then forward, you could buy compressors either with or without the feature. Corvette used the feature and the factory stock engine A/C harness should sport the appropriate connector...

Essentially, the switch installed in the rear plate of the compressor and was normally open. When/if, the compressor lost refrigerant (and its embedded refigerant oil), internal temp would skyrocket as the compressor began to sieze.

The 'super heat' conditions triggered the bi-metal switch to close and that effected a short to ground (through a current limiting resistor built into the wiring harness connector) to rob power from the compressor's magnetic clutch. Without current through the magnetic clutch, it'd release allowing the compresor drive shaft to 'free wheel' and keep the compressor from doing further damage to itself.

The last time I ordered an A6 from Delco, you had essentially two construction options: (1) with/without superheat switch, and (2) SAE or metric. It was the mechanic's responsibility to option the replacement compressor correctly for the target vehicle.

[Jack H.]

Re: A/C Compressor Heat Switch?

One postscript here... If you ordered a replacement A6 from Delco WITH superheat switch, it came WITHOUT the switch installed! It simply had the rear plate with provision for mounting the switch...

It was the mechanic's responsibility to REMOVE reuse the existing switch from the failed A6 BEFORE it was turned in for core credit! I've seen MANY mechanics pull their hair because they ASSUMED the replacement A6 would have the switch installed and they blindly turned in the original for core credit WITH the switch still installed...

[Alger R.]

Re: A/C Compressor Heat Switch?

Great information! My follow up question is this... My back plate which does not have the switch provision has the embossed number 6555302 and a date code of A035 (Jan 3, 1975). The green label has the model # 5910741. All the numbers seem to tie in with the 75 Corvette numbers but yet no switch provision? Would there have been a non switch option on any factory Delco Corvettes or other models?

[Wayne M.]

Re: A/C Compressor Heat Switch?

..... I've seen MANY mechanics pull their hair because they ASSUMED the replacement A6 would have the switch installed and they blindly turned in the original for core credit WITH the switch still installed...

Jack, how do you remove the heat switch ? Looks like you might have to take off the rear head .

[Dick W.]

Re: A/C Compressor Heat Switch?

Wayne, remove the snap ring and manuver it out using a pair of duck bill pliers

[Alger R.]

Re: A/C Compressor Heat Switch?

So now I am confused and worried that my 75 Compressor is incorrect? Attached is a pic showing the rear plate and date code. It appears that the A6 back plates were numbered 6556406 for the heat switch variety and 6555302 for the non switch variety. Mine is obviously the non switch variety with a 75 date? I guess I am hoping against hope that maybe some 75's didn't have the heat switch. I would appreciate more comments. Thanks, AL

[Jack H.]

Re: A/C Compressor Heat Switch?

Can't confirm/deny... Check your copy of the AIM (or Chassis Service Manual) wiring diagram and see if it calls out a branch wire servicing the super-heat switch.