I have a Mustang convertible with a six cylinder engine...

Dear Car Talk

Dear Car Talk | Jul 01, 1994

Dear Tom and Ray:

I have a 1983 Mustang convertible with a six cylinder engine. Everytime I turn on the defroster to clear the windshield, the compressor comes on and the engine idles much faster, which makes it dangerous on slick streets. How do I go about disconnecting the compressor from the defroster before next winter, since I don't need the air conditioning in the winter?

TOM: Don't go disconnecting stuff so fast, John. A simple adjustment ought to fix this for you.

RAY: The air conditioning compressor is switched on when you select "defrost" because the air conditioner removes moisture and helps clear the windows. In fact, it helps a LOT, which you'll discover when you ignore our advice and disconnect it anyway.

TOM: Since the air conditioning compressor draws a lot of power from the engine, most modern cars have a device that kicks up the idle speed to compensate. That's supposed to keep the car from stalling or running rough while the compressor is on. And if it's working properly, you shouldn't even notice it.

RAY: But in your case, the idle speed is being boosted too much. Adjusting the idle-up mechanism will take care of it, John.

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