Power wire to compressor?
 

My 72 Lemans is now up and running. The only thing left is to get the new Classic Air AC system evacuated and charged. O have left the power to the AC compressor disconnected so it can't inadvertently be engaged.
I decided to check power at that wire just to make sure all was good. Not good.
I may have the wrong wire. The old AC compressor had a plug with a green, a short black with a half round plastic fitting (which I think is the overheat wire), and a brown. I assumed the brown was the power wire. It has no power while the AC is switched on and blower blowing. I need to know what wire I should be looking for power to plug into the new one wire compressor.

There should be a pressure switch before the compressor on that wire. If you have no/low refrigerant there will be no power to the compressor. No refrigerant, no oil circulating to lube the compressor so the system shuts down.

AC clutch power wire is green.

Clay

Looking at the schematic, that's what I was thinking. Thank you. Another question. As I look at my original A6 compressor off the car, the only electrical connection I notice is a stud which I assume is where the black plastic capped connector must go (I think for the super heat or whatever it is called). Is that actually the only power source to compressor?

Clutch is the only thing that gets power. 2nd terminal is for the clutch ground wire.

Newer stuff (reciever drier) had the clutch ground bolted down at one of the mounting holes.

POA(?) had the pressure switch on back for clutch ground.

pretty sure that's right
Clay

My A6 clutch line has a 30A fuse. Size the wire accordingly.
Might help to know what brand/model your new compressor is.

It's from Classic Air. I'm pretty sure it's Sanden. It only has one wire for power. Instructions say to use old power wire from old system and hook to pressure switch that then goes to compressor. I bought the car apart and AC off. There was a brown wire from engine harness that led to a one inch plastic terminal holder with a green wire and a short black wire with ring terminal (ground?). That brown wire was the only wire I figured could reach the old A6 from where it was located. So, I assumed that was power. But, in my harness, there is also an unused green and black wirein one inch plastic terminal next to the bigger plastic wire block for TCS, etc that looks just like this other one. But, they don't plug together since they are the same. I did check that other green wire from that for power with key on and AC switch on and blower on, but no power to that. I was thinking that would now be the power lead I was looking for. I'm still not sure how the factory wired the original I have.

Power wire is a green wire that comes from the ambient temp sensor on the pass side cowl. No pressure switches on those models. They use POA valves. Compressor runs all the time if ambient temp sensor is closed.

Originals were wired to run all of the time. Some time in the 70's they started cycling the compressor depending on the commanded temperature.

CCOT came out in 1977 models.

Thanks guys. I'll check for power at the ambient temp sensor green wire in the morning and respond to what I find out.

An idle kicker solenoid is always nice.

I actually have that, but was told I don't need it since this system doesn't draw as much power as the old system.
I found power. It was actually the brown wire I thought it should be. I'm not sure if my test light wasn't getting a good ground or what. That harness that ran to the old compressor is powered by the brown and the other leads within the plastic junction terminal of green and black fed the compressor.
Now another related question. I thought that power wire would be feeding power to the compressor on AC, bi-level, defrost, but it also stays powered on heat and vent. Is this normal?

Compressor runs on all top positions. Only when you slide the "norm-vent" lever does the compressor quit. I have a `71, so the `72 should be the same.

I have a 600hp 463 with a sanden compressor. You would be suprised how much that idle solenoid is needed.;) At least on mine with a 246/253 cam.

I guess I'll find out Wednesday when I go to get it evacuated and charged and start using it.
Thank you very much for the controls tip Punch. I just checked and the only time the power to wire is cut , is when Normal is slid to Vent. I'm not used to the control functions, so whenever you run the Heater, do you run in the Vent mode?
How about the Inside mode? I do know Bi-Level, AC and Defrost run off compressor so then needs to be slid over to Normal mode. Thanks again. MUCH!!

"Inside" mode is recirc or max ac. One can leave it in norm for heat but, I use vent to not run the compressor while I`m trying to heat the air.

Thanks. I looked in my file and I actually bought an owners manual a few years ago. It explains it all.

Most people don't know this, but to this day AC compressors still run in the winter on defrost, on new cars..

Or old cars.