A/C "clicks on" when I turn the fan motor on with heat

Cougar Community Classic Cougar Maintenance Restoration and Repair
1

After replacing the coolant / hoses, I filled it up to bring it to temperature and decided to run the heater as well to verify heat is coming out of the vents.

In doing so, I noticed the a/c compressor appears to “click on” when I turn the fan on in the heat or defrost mode…I assume it should only activate in the fresh / max mode. Is there a reason this should be happening? Suggestions on what I should look at?

I’m getting ready to drive to Wisconsin in a few days (family, Road America races), and may have to follow-up on this when I return in 10 days.
Heater ac controls.pdf (541 KB)

2

Just to be clear - this is a purely OEM Mercury AC? Later aftermarket units like Vintage Air will run the compressor when the heat/defrost is on like modern cars to dehumidify the air. Not sure when OEM units started doing that.

3

Yes, its all OEM at this point.

I had a chance to look through the service manual and search through this forum before heading out on vacation and found power is supplied from the blower switch, then goes to a clutch switch, and then to the temperature/icing switch, and finally the compressor.

The service manual doesn’t provide any explanation in how this clutch switch really operates (unlike the other components), but it does show (page 16-15, figure 6) the clutch switch should be off when the function switch is in heat or defrost. I’'ll have to look to see how the “plunger” on this switch is activated as the function selector is moved.

For now, I’m going to assume this switch is stuck in incorrect position for now until I have a chance to look at it in a few weeks.

If this switch is bad or I can’t clean / fix it, I wonder if I can do a slight mod and use a new one from a 1969+ system since the 1968s only appear to be used and a bit pricey?

4

Back in the 1970’s and 1980’s I was driving a 1967 with factory A/C. I used to unplug the clutch wire during winter months to keep the compressor from coming on.

5

From the description in the WCCC site on how the switch is activated you could have a stuck air damper holding the switch closed.

6

Just to confirm, are you saying the ac compressor is always on no matter what you select on the control switchs?

7

The AC compressor is “On” anytime the fan is on and the icing switch is closed, IE the icing switch does not detect icing in the heater core or evaporator.