Questions and Answers

Defroster Problem Q. I have a 1991 Grand Am with a front defroster problem. When moving selector on the heating system it blows a fuse. Changed fuse and same problem. Then pulled heating and A/C control unit out to look at problem couldn't find problem.

A. It goes without saying that there is a short somewhere in the system. Where? It could be in the blower relay, A/C compressor clutch wiring or A/C relays.

You're going to need a wiring diagram to isolate the problem. You can unplug the A/C compressor first to eliminate the A/C clutch. But from there on it's a matter of checking each section for a possible short.

Since the mode doors are vacuum operated, it at least narrows it down to something in the A/C or blower motor.

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