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George H.
George H., ASE Certified Technician
Category: Toyota
Satisfied Customers: 18622
Experience:  ASE Master Tech 15+ years
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1991 corolla: blower fan..Resistor set is good and CB is..Fan works

Customer Question

1991 corolla blower fan not working. Resistor set is good and CB is good. Fan works when hooked up to a 12volt source, but not when installed. Heater & AC work, but need ram air.
Any ideas?
Submitted: 7 years ago.
Category: Toyota
Expert:  George H. replied 7 years ago.

Hello I will help youu with your question,


If you jump across the two large terminal sockets of the blower/heater relay will the blower run? Can you then control the speeds? There are a couple of possibilities, the relay may have failed or the blower switch might have given up. Here is the wiring diagram and you can see the relay at the upper right quadrant and the switch at the lower right.


Let me know if you can jump the relay (only the large terminals, they should be copper colored) if you have ANY question don't do it and I will see if I can find a diagram of what to jump



Customer: replied 7 years ago.
Well, I am not with the car right now. Some additional info. When all is installed and I move the speed control from 0 to 1+, I do hear a click coming from the CB - Heater Relay area of the car-passenger food well. I am not too sure about how to jump the Heater Relay.
Expert:  George H. replied 7 years ago.

OK that means that the switch is turning the relay on so you might be OK. The relay can turn on without making contact so you will still have to try jumping the relay. Use a large paperclip to jump the terminals 5 to 4 on the heater relay as shown below




You posted that the resistor is good? How did you determine that?





Customer: replied 7 years ago.

Well, the paper clip didn't do anything. I found the same relay in the engine compartment & switched them-still no fan. The initial fan failure was intermitent, and then finally never any fan at all. When I have tested the fan, & it does run, I just hooked it up th the battery. Do you think the fan itself is bad ?

Expert:  George H. replied 7 years ago.

If the fan runs then the switch has failed.


Use a testlight to check for power to the switch. This power comes through the blower motor so you should have full battery voltage at the black/white wire at the switch and if you move the switch to the high blower position the voltage SHOULD change to ground or 0 volts. If this does not happen then the switch has failed or the ground for the switch has failed.


There is a connector to the left of the blower motor and it has the connections to the switch form the motor and the resistor.


Here is one method of checking the switch, I prefer a testlight as it dynamically test the operation.


If the fan runs it is not bad, it is time to get a testlight and follow the power from the blower motor to the resistor block to the switch.





Customer: replied 7 years ago.
Ok. I did not get to this on Sunday. I will be working on the car again, this afternoon and let you know what I find out. Thanks.
Expert:  George H. replied 7 years ago.

OK, great, I will be on all afternoon and evening. Thanks for leting me know and let me know what I can do to help.



Customer: replied 7 years ago.
I'm back. Sorry about yesterday-I had to fix a gate and that took longer than expected. Anyway, from the switch, with everything installed, there is power to the fan ( comfirmed by test light ) in all 4 speed positions, and no power to the fan in the off position. What do you make of this ? Recall that the initial failure was intermittent - sometimes a bump would start the fan and also ram air speed seemed to start it.
Expert:  George H. replied 7 years ago.

If you have power at the black/white wire with the switch in the high position the switch has failed.


Check from the black/white wire to the white/black wire with the switch in the high position, if the light comes on the switch has failed.


Let me know what you find





Customer: replied 7 years ago.
I'm still out here. I checked the continuity of the switch and it is good. I even pulled one from the junk yard and it tested the same. ( I did find one that had burn damage) I used the Haynes manual instructions for testing the switches. The resistor set is new. That is what I initially thought was the problem since it was the original resistor set was badly corroded-from my experience with small cars, this is usaully the fault with fan problems. The new resistors did seem to help at first, before complete failure-I then suspected the fan, but it "tests" fine when hooked up the a 12volt source. Looks like I need to go back and recheck everything.
Expert:  George H. replied 7 years ago.

Use the voltage drop testing to find where you have voltage that should not be there.


In the high switch position you SHOULD show full battery voltage before the blower motor, you SHOULD NOT show more than 1/2 volt at any point after the blower motor.


If you reverse the leads and have the black lead on a positive voltage source like the positive terminal of the battery you SHOULD show voltage AFTER the blower and less than 1/2 volt before the blower motor.


If both of these checks are good then you have a bad blower motor or the connector to the blower.



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