A/C keeps blowing fuse

[jgerock]

My 73 has Behr AC so the stock wiring details can be found in the archives.

 

Square relay for the fan in the engine bay (right side)

Another relay under the dash

Edited July 1, 2018 by jgerock

[grotflo]

Update time.  I've crossed a few things off the list of potential problems.  The blower switch is good, as is the wiring from that to the blower.  One odd thing to note - the high blower setting only blows the fuse when the car is running.  When the car is not running and the ignition is turned to the "on" position, it works fine.  But when I start the car, setting the blower to high blows the fuse.  I can't think of anything that would cause an increased current draw only when the engine is running.  Any thoughts?

I think I probably need to go through each wire in the fuse box and see if anything is hooked up incorrectly.  And a good cleaning wouldn't hurt either.  But still, it's weird to me that the car running affects this.

[Tsingtao_1903]

Just a guess.  When the car is running, it is possible that in your car, the voltage the blower sees dropped (power is equal to voltage times current)?  If this is the case,then, it will draw more current to compensate.  The fuse sees more current - pop.

 

[grotflo]

Hmm, yeah that's a possibility for sure.  I'll put a multimeter on it today and see if it's getting less voltage when it's running.  If that's the case, what is the solution?  Bad battery maybe that's not providing the full voltage?

[grotflo]

Battery checks out, no problem there (12.6V off, 13V running).  The terminal on the fuse box that the blower's hooked up to puts out 12.8V while running.  So that's no help.  New plan of attack: clean fuse box to remove all oxidation, disconnect compressor clutch and see if that changes anything, then if needed, figure out how to test the blower motor w/o removing it from the car.

[HBChris]

Just some background:  Power to the A/C system first goes through the temp switch, then to the fan speed switch, then to underhood relay.  The relay only actives the condenser fan, power to the pump breaks off at the relay but doesn’t get power from the relay.  Power for the condenser fan comes direct from the battery, the relay is the trigger for this fan.  The relay under the dash if there, and if same as e9, is a cutoff relay to remove the heater fan from activating when A/C is on.

 

I would check the circuit beginning at the temp switch with fan wires disconnected, then check fan speed switch itself with wires at underhood relay removed and then move to the relay.  There is a good chance it is the fan speed switch.  Good luck.