I recently bought a 2003 Grand Marquis. It has the electronic automatic temperature control (EATC) heating/ac system. It was a cold day. Several days later when it warmed up (about 40 degrees) I switched from floor/defrost mix to max AC. The air flow from the blower did not change from blowing out the defrost to coming out the vents. Any setting for vent, floor, mix. or defros does not change the blower airflow from defrost to any other location. Also when I set it on max AC the clutch did not engage on the compressor.

Do I need to replace the whole EATC head unit, or is it something else?

 

Check your fuses first. (of course, if it's a digital one and you have a readout, I doubt that's the issue)

You may need to check and see that everything is actually connected to the controller too. Sometimes wires wiggle loose and vacuum lines may be open as well (if they still use vacuum to actuate the vents).

 

My climae control digital brain died, I currently have all the door control solenoids on the floor and hotwired. Heat and defrost now switch, but fan runs full blast only.
If it wasn't for that broken shaft on the blend door I'd buy a new brain

 

I've posted about blend door fixes I've found on the net before...

Here's the links to check out.
http://www.blenddoorfix.netfirms.com/
http://www.conceptualedge.com/blend-door/

If you're handy with stuff (which it sounds like you are) you can fix it yourself.

 

The first one doesn't look to bad, but outside in sub zero, was unable to get my fingers enough room to remove actuator. And when it gets warm still looks like a killer. Used a screwdriver and opened blenddoor to heat for winter.

Second one, that definatly looks like a project also. But fortunately I have the required dremel, maybe in the spring!

Brain runs ?$?, saw 1 on ebay for $50, but after a few ----, no longer shop there. Refuse

 

no clue on the price of the controller. You'll probably have to call a dealer. Check out rockauto.com as well. They tend to have close to everything.

 

Yeah,sounds like the module is bad (module is contained in head).
You can check for sure by monitoring the blend door or fan circuits with a multimeter while actuating it.
These things aren't cheap new from the dealer I know,but at least I don't think it has to be programmed in by dealer.

 

It's a known defect. My mom's '07 went in for it and was replaced under warranty.

 

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