A/c compressor does not disengage?

[Jannelu]

I have noticed that on my 76 Continental Town car, the a/c compressor does not disengage when i turn on the heat.
In the low and high position it runs at all time regardless of which temperature i choose, the same at defog and defrost positions.
Even at full heat, the compressor is running and the a/c line gets cold and frosty.
The only time the compressor disengage is at the off and vent economy positions.
I have searched the shopmanual for a description of the different lever-positions to find out when the compressor should engage but i cant find the info...
Otherwise everything seems to work perfect, icecold a/c and the heat is also good.
It just seems unnecessary to run the compressor to warm the car up.
Someone got a clue?

[action]

The compressor will be always be on during defrost and defog.
This is to take out moisture from the air being directed at the windshield.
Moist air on a cold windshield means the windshield will fog up. Or worse create ice on the inside.

Pretty sure the compressor should be off during heat on the floor.
Or as you state during fresh air vent.

However if the system is ATC versus manual AC the compressor may be on.

Action

[Jannelu]

Thanks Action..
Its Atc, automatic temperature control system.
So possible its nothing wrong?
Seems strange though, to run the compressor when heating is required..
Well well, its an old car and old system, hopefully everything is as it should.
Any other 76 Town car owner out there who can shed some light on the matter?

[Dan Szwarc]

I can. 70s Lincolns regulate the temperature by adjusting a blend door. One side is cold, the other side always hot, and the door position is adjusted based on the delta from the set temp.

It’s terribly inefficient, but toggling the AC compressor was beyond the electronic abilities of the time. And it’s all done without software or digital controls. The system is totally analog, even using vacuum pressure to position an arm inside the brain to control the blowers and blend door.

[Jannelu]

Ok, thanks Dan.
Thats what i hoped for, everything work as intended:))
An idea that pop up in my head is to install a hidden switch to turn the compressor of when its not needed, that should be a easy fix, just route a cable from the compressor to a switch underneath the dash or at some other invisible and accessible place.
Any thoughts about that?

[Dan Szwarc]

Installing a kill switch for the compressor is a fine idea. It’s been done. Just open one of the two wires going to the clutch.

[Dan Szwarc]

If you want to learn about your ATC system, the best I can do is 1977 and a thread from navguy12.

ATC; 1977 Continental, no ATC fan on auto settings

[jon schapiro]

My ATC runs the compressor only in LOW, HIGH and DEFROST modes. VENT mode it disengages.

[Jannelu]

Doesnt it run in the defog position?

[jon schapiro]

Read my response above your question

[Jannelu]

Well, you wrote that it runs only in low, high and defrost and that it disengage in vent, nothing about disengage in the defog mode, hence my question.

[jon schapiro]

I stated in runs in Low, High and Defrost

[jon schapiro]

I stated in runs in Low, High and Defrost

[Jannelu]

Thanks...

[TonyC]

I have a question, which may help me give clearer input. Jannelu, Jon, does the '70s system have separate DEFOG and DEFROST settings? If so, that could make a difference in what I have to say, based on the '60s controls.

---Tony