1971 Mark III Heater Operation

[stovebolt1]

Happy holidays all!

I noticed today that when I have the ignition turned on, but the engine not running, that the heater/ac fan does not turn on. Is this normal? The fan does turn on when I select the Defog or De-ice options without the engine running. Reading through the manual it looks like the heater won't engage until the engine temp reaches 125F. Is this another clever/quirky feature for the Mark III ?

I can hear the A/C clutch engage when I turn the ignition on/off so I think that is a good sign.

Thx - Stovebolt

 

[Action]

For all cars not just Mark III.

When the defrost function is selected either as a stand alone or floor defrost, the AC compressor is engaged. A function of the AC system is to remove moisture out of the air. On a cold windshield, when moist air is being blown on the windshield, the moisture will cause ice to form on the inside of the windshield. Any time air flow is directed to the windshield the AC compressor will come on. True for standard AC or ATC in any flavor.

In an (E)ATC system set to heat and air flow to floor or vent mode the system will not operate until a certain temp is reached.
The exception is defrost mode or any mode that blows air to the windshield.
It is designed that way to provide windshield clearing function as soon as possible. Any air movement can help clear the windshield in some circumstances.

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