why does my heater only work on defrost on 2005 Grand Marquis,AC works the same way
My climate control only works on defrost when blowing hot or cold. Would
removing the face control and cleaning contacts help?
I show two systems for Mercury, one just has normal buttons and sliders on the control head the other is digital, both systems use servos to control the blend doors, one system uses vacuum servos the other uses electronic servo motors, so if your uses vacuum servos the default position is defrost if you loose vacuum, the other system uses a set of codes that can be access through the the dial display but it has to be done right or it can be misdiagnosed. So if your not very mechanically inclined I would take this problem too a shop you trust, it does not have to be a dealer, most good independent shops can handle this repair. HTH
I had the same problem on my 1998 grand marquis. I had to replace my climate control.
Temperature control modulator. YouTube how to bypass it. Super easy
Have a 2003 Merc Marq. LS with climate control. Same problem. Dealer told me new module, for $600 plus install. Researched and found out the design was bad because of a weak chip inside module which controls air flow, etc.It fries when interior gets too hot. Bought a used module for $100 and put it in myself. Worked fine for 3 months. It fried, same symptoms. Found a company in Van Nuys, California replaces chip and remans the module the way it should have been built. That was 5 years ago and haven't had a problem since. Company is Module Repair Pro. 5 stars in my book.
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