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I have a 1989 Chevy Cavalier and the heater keeps blowing fuses. I have replaced the blower motor, blower motor resistor and the heater switch, but the fuse still blows as soon as I turn the heater switch on. I thought about replacing the blower motor relay, but an AutoZone rep told me that the relay would not cause the fuse to blow. Any help with this problem is greatly appreciated.
 

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Good Afternoon flash4446151, the heater blower circuit generally has a variable speed switch and may be controlled by a relay.

The heater power should originate from the accessory circuit, but in the case of a relay controlled motor that motor power may have a different source.

In that your fuse keeps blowing it is entirely possible that the actual relay has a shorted coil or problem like that.
Relays often contain a diode across the coil that can do that.

Try removing the relay and inspecting the socket and then see if the fuse still blows.

If the fuse blows with the relay removed I would expect an underdash wiring problem or mis-wired heater circuit.

If the fuse only blows with the relay fitted, try another relay or closely inspect the motor wiring circuit and speed control switch for miswired or short-circuiting wiring.

That is a pain working underdash on some of those cantankerous problems.

Cheers, qldit.
 
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