Rich123

I just got my AC working on my 78. We put a new compressor and dryer on after the old compressor seized.
Question:
After the ac has been on for a while and the inside of the car is cool, should the compressor disengage if I move the temp control to the right (warmer). Mine does not seem to.
I know on some cars the compressor cycles to maintain temp and others use a bypass around the expansion valve to maintain temp.
Does anyone know for sure how this one works?

Also, if the system is overcharged a little, will it create a bigger load for the compressor?

Thanks

toobroketoretire

It continually spins.

Rich123

Does that mean the clutch is continuously engaged if the control is set to AC?

Rich123

Took it out for the weekend up in the mountains. I have disconnected the lines to the heater so that there is not any heat coming in AT ALL.

The AC works great, but when I moved the control to the right it did not reduce the cooling. The air coming from the vents stayed very cold.
I would have assumed that this car would have some kind of sensor to detect that we were freezing in the car or that the temp control was try to communicate that we had enough ice cubes already and would automatically backed off the cooling. Is that a bad assumption? Is the only regulation device going to be my right hand to shut it off for a while?

Encore00

Hey Rich,
that doesn't sound right. I don't know much about the system but my 81 toggles the compressor clutch to regulate temp.

Encore

76vette1

I believe there is the a/c pressure switch on the right fender that shuts the compressor down when the freon gets low and there is a compressor control switch on the plenum that senses the evaporator temperature to cycle the compressor. At some point, someone may have unplugged it and put a jumper in to make the compressor run all the time.

Rich123

Thanks, I'll look for those. Something unplugged on this car is not uncommon

vbgod1

2 things I would venture.

I think you have a CCOT, cycling clutch orifice tube, which means it should cycle the compressor clutch.

I also think you have a "reheat" system, meaning, unless you are on Max cold, the air also goes through the heater core, warming it up a bit before putting it into the cabin. If the water valve is off, you will be on "MAX" at all times for cold air.
You should have a low pressure cut out switch, that shuts the system down if the pressure is too low, and a thermostatic switch, which I believe is what cycles the compressor, clamped to the evaporator line.

Easy Mike

Yep. Disconnecting the heater hoses means the AC air cannot be warmed up.

Rich123

So, if I connect the heater hose up that might make the compressor cycle?
I looked and there is something on the AC low side line. It has wires attached to it. One of them is the same color as the compressor wire. This looks like a good place to start.
Thanks

Jud Chapin

Yes, the a/c will always be at its max cold with the heater disconnected as the temp control adds warm air as it is moved to the warmer positions with the heater connected.

Rich123

My mistake, the "something" (I guess a sensor) is on the high side line. It's after the coils up front and before the coils inside the car.

vbgod1

Don't think it will make the compressor "cycle", but should warm the incoming air a bit.
I think the thermostatic switch is what causes cycling (from memory, no literature here this late).