Modern add to AC System A6 Compressor

[PbFut]

I was under a misinformed impression it was not good to cycle A6 compressors. 1970cstblazer reminded me that A6 systems in the late 70 and 80 did have a cycle to them. And it seems more Aftermarket systems are modifying or changing POA valves to electrically cycle the compressor. My early 80s 3500 truck did. So with that in mind....
While I am rebuilding the fire damage AC system, I am going to ad 2 switches in series to the clutch power line. One is a Thermostat switch to monitor the temp of the evaporator to eliminate freeze up issues, the other is a Tri-switch to monitor high/low pressure conditions on the high side refrigerant line. Both switches in series would interrupt the power to the compressor clutch should any of the conditions fall outside of acceptable range. I am not sure of the amp load of the compressor nor the capacity of the switches, but it is not difficult to add a relay to the mix if needed. Doing this protects system form High or low pressure state and evaporator freeze.
Can I get a quick reply from those in the know, if this is a good idea or not. If not why?
Thanks for help.

[Steeveedee]

Note that the R4 compressor has a much bigger clutch. I've seen where people were cycling the A6 and tearing up the clutch over time.

[1970cstblazer]

Not sure if GM bolstered the A6 clutch in 1976-79 controlled cycle systems prior to the change to R4 compressors. I have put many miles on the two I currently own plus other 1976-77 Pontiac cars I've previously owned, and never had an A/C clutch failure on them.

[Steeveedee]

I was a mechanic with an NIASE cert (before it became ASE) for AC among other things. I don't recall ever seeing a CCOT system with an A6 compressor. I could be wrong, as sometimes happens.

[RustyPile]

Originally Posted by Steeveedee

I was a mechanic with an NIASE cert (before it became ASE) for AC among other things. I don't recall ever seeing a CCOT system with an A6 compressor. I could be wrong, as sometimes happens.

I too, was certified during that period.. And I don't recall ever seeing a CCOT system with an A6 compressor. I might add, that during my "stint" as a mechanic, I replaced far more R4s than A6s.

[Steeveedee]

Originally Posted by RustyPile

I too, was certified during that period.. And I don't recall ever seeing a CCOT system with an A6 compressor. I might add, that during my "stint" as a mechanic, I replaced far more R4s than A6s.

That cycling clutch had to be a strain on those compressors.

[MARKDTN]

Originally Posted by Steeveedee

I was a mechanic with an NIASE cert (before it became ASE) for AC among other things. I don't recall ever seeing a CCOT system with an A6 compressor. I could be wrong, as sometimes happens.

We had a '77 and '79 Bonneville and I worked on a '78. All had cycling A6s. Don't some later BB Square bodies have A6 compressors that would be cycling?

My uncle had an 70s John Deere tractor with an A6 and I'm pretty sure it cycled but can't say with absolute certainty. Also we had a '79 Ford LTD with an A6. Again I'm pretty sure it cycled but can't say with absolute certainty.

I removed the POA valve and put a cycling switch kit on a '67 Firebird and a '71 C10 for others, both with A6 compressors, and as far as I know both are still running fine. I know a lot of people don't like those kits but both of my customers were happy.

Now with all that said, I would not put a new A6 on anything. I would swap to a Sanden. I think efficiency and life is much improved from what you can get from any A6 you can buy today. Any cycling is not an issue.

I probably have 10 old A6s that are going into the next scrap metal run. Just no demand and too much downside to putting a used one on anything. One of them is original from a '68 Camaro but what good is it?

[Steeveedee]

Originally Posted by MARKDTN

We had a '77 and '79 Bonneville and I worked on a '78. All had cycling A6s. Don't some later BB Square bodies have A6 compressors that would be cycling?

My uncle had an 70s John Deere tractor with an A6 and I'm pretty sure it cycled but can't say with absolute certainty. Also we had a '79 Ford LTD with an A6. Again I'm pretty sure it cycled but can't say with absolute certainty.

I removed the POA valve and put a cycling switch kit on a '67 Firebird and a '71 C10 for others, both with A6 compressors, and as far as I know both are still running fine. I know a lot of people don't like those kits but both of my customers were happy.

Now with all that said, I would not put a new A6 on anything. I would swap to a Sanden. I think efficiency and life is much improved from what you can get from any A6 you can buy today. Any cycling is not an issue.

I probably have 10 old A6s that are going into the next scrap metal run. Just no demand and too much downside to putting a used one on anything. One of them is original from a '68 Camaro but what good is it?

I stand corrected. If I ever saw one, I don't (obviously) remember.

[Bob B.]

Originally Posted by Steeveedee

I was a mechanic with an NIASE cert (before it became ASE) for AC among other things. I don't recall ever seeing a CCOT system with an A6 compressor. I could be wrong, as sometimes happens.

I think I saw CCOT systems with A-6 compressors on some big commercial trucks in the very early 80's. Maybe only on diesels (lower R.P.M.'s?). A lot of the 'VIR' (valve-in-receiver) systems had A-6 compressors, but they didn't cycle.

[1970cstblazer]

VIR, especially on Pontiacs, ended in 1976.

[Wrenchbender Ret]

I changed over from a R-4 to an A-6 compressor years ago on a 87 Monte I was driving. When it kicked on it make little screech noise & felt like it had a miss fire in the engine. It took a lot of power from the 305 engine to run it. I never had any trouble with it though. I drove it many years after that.

George

[PbFut]

In this case I am not cycling as a substitute for the poa valve. I am using the thermal switch solely as a precaution to freeze up do to multipal causes and get me to a point I can diagnos. The pressure switch would be to protect compressor from low refrigerant or a failed fan causing high pressure state. If the A6 system is working correctly none of these states would occur and the switches would remain closed whereby not cycle the compressor and work as originally designed. The two relatively inexpensive switches would be in place simply as a precaution while adding only 2 simple devices into the factory electrical path. Or I am overthinking an issue not needed.

[RustyPile]

Originally Posted by PbFut

In this case I am not cycling as a substitute for the poa valve. I am using the thermal switch solely as a precaution to freeze up do to multipal causes and get me to a point I can diagnos. The pressure switch would be to protect compressor from low refrigerant or a failed fan causing high pressure state. If the A6 system is working correctly none of these states would occur and the switches would remain closed whereby not cycle the compressor and work as originally designed. The two relatively inexpensive switches would be in place simply as a precaution while adding only 2 simple devices into the factory electrical path. Or I am overthinking an issue not needed.

Dan, you don't need a thermal switch.. A properly functioning POA does just that.. It controls the pressure in the Evaporator to a predetermined value (depending on the refrigerant) and THAT prevents freezing.

[PbFut]

Originally Posted by RustyPile

Dan, you don't need a thermal switch.. A properly functioning POA does just that.. It controls the pressure in the Evaporator to a predetermined value (depending on the refrigerant) and THAT prevents freezing.

Low confidence in my calibration skills.

[PbFut]

Agree more modern compressors are way better. I have this odd thing about me that I like that old familiar look to certain key parts of the engine bay. Which is odd since I am going the Hydroboost route, and did run, and may still, a 8 stack TB setup. So it's certainly not a "original" truck. I guess because I can get the A6 to acceptably perform I choose to say with it. The carburetor perform but I swapped that so who the heck knows why I do things.

[Cali72K20]

Did you look into this possible option?

https://www.originalair.com/vir-elim...-equipped-only

[Cali72K20]

Are just adding as a precaution?
Found an old GM HVAC training book from 1995 and looks like you are making wiring harness similar to this?
With switches similar to these?

[PbFut]

Hey Casey
Yes that is the general idea.
Our system would require the Tri switch in the high side line. I figured an adaptor tapped at the hose to tube fittings down by the Battery box/radiator support would be good and not too visible. The Thermostat switch up on the Evaporator pipe where the valve sensor is now under the black asphalt stuff. The switch may even be able to hide in the housing. Easy to daisy chain the switch connectors in the compressor clutch line.

[PbFut]

So in conclusion. A cycled A6, probably not the end of the world, but may not be advisable either.
Adding a thermostat switch on the evaporator is probably useless as you would know you are froze up because the air flow will be reduced. Low pressure state is easy. Air will not be as cold as before. High pressure would only happen from improper filling or a failed fan and the engine would be running hot with failed fan. So in reality, though these safety switches may function on our system, there does not seem to be enough benefit to add complication to what is a pretty simple system that functions quite well as is. Thanks to all that participated. I found the discussion informative and a bit entertaining. Now back to cleaning and sanding.