Fuse blows when A/C is turned on

ANGLMBABY2360

MEMBER
1998 MERCURY MYSTIQUE
1.8L
4 CYL
2WD
AUTOMATIC
120,000 MILES

If I'm driving down the road and turn on my a/c, next time I put it in park it will not move out of that gear. When this happens my lights stop working, fan in a/c stops working, and the car won't come out of gear. I temporarily fix it by putting a new fuse in but it still has me re framing from using the air. What do you think could be causing my fuse to blow? Crossed wires? Fused wires, possibly?

Tuesday, October 21st, 2014 AT 7:38 AM

1 Reply

CARADIODOC

MECHANIC
34,164 POSTS

You have a short circuit. That fuse feeds a lot of circuits but you already have a major clue staring at you. We know it's related to whatever the AC / heater system is controlling. The logical first guess would be a shorted AC compressor clutch coil. Unplug that, then see if the fuse blows when you switch the AC on.

If it does, a simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

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Tuesday, October 21st, 2014 AT 8:31 PM