Does my AC need a new blower motor or just a new switch?

Dear Car Talk

Dear Car Talk | Feb 01, 1995

Dear Tom and Ray:

I own a 1986 Chevrolet Celebrity with 87,000 miles on it. I pulled into my driveway one day last summer when the temperature was very hot (about 90 degrees). I had just driven about six miles, everything seemed normal, and the air conditioner was on with the blower fan on "high." I turned off the car to go into the house, and the blower fan would not shut off. It continued to run on high speed. Neither the ignition switch or the fan switch would turn it off. I opened the hood and pulled the wire off the blower motor. The blower motor stopped. I reconnected it, and it was fine until it recently happened again with the heat on. Again, I had to pull the wire to get the blower to stop. How do I fix it?

TOM: You just did, Ralph.

RAY: If you want to fix it on a more permanent basis, you'll need to find the blower motor relay under the hood. On high speed, the relay acts as an intermediary between the fan switch on your dashboard (real cheap switch that can't handle much power), and the blower motor under the hood (more expensive part that needs lots of power). So when you flip the fan switch on your dashboard, you're actually activating the relay, which is basically a heavy-duty switch. Then that relay turns on the blower motor.

TOM: So it sounds like the relay is sticking in the "on" position. A new one ought to fix the problem.

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