Heater blower motor not working

Good evening,

You are correct. The fact that when you ground the wire and the motor does not work points to the motor, but you are assuming the resistor assembly is grounding the wire. If the resistor is bad internally, then it explains it. Just apply a ground directly to the wire to the resistor and see if the motor works. That will confirm the motor.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/blower-fan-motor-works-on-high-speed-only

Roy

Roy,

Thank you very much for your quick reply to my question. People like you help out a lot by sharing your expertise.
I also want to thank everyone who shares his/her knowledge and experience with DIY community. I came across a 30-minute video on YouTube that explained in very detail starting from putting heating system in diagnostic mode to every component involved in heating system.

Yes Roy, I made sure that Ground terminal on resistor (electronic circuit involving MOSFET which acts as a variable resistor in motor circuit which controls speed of blower) is in fact was Ground. I checked this with continuity test directly from car battery negative terminal to the black wire (ground) on the resistor plug. External jumper wire effectively shorted MOSFET Source and Drain terminals providing direct ground to blower motor. This did not start the blower. So, I assumed, blower motor was faulty. I removed the connector from the blower motor and removed the entire blower motor. I then applied 12 volts directly to motor + and - terminals from battery by two jumper wires momentarily (eliminating any other component or wire in blower motor circuit). Instantly blower motor started. To make sure, it consistently works, I again applied voltage, but blower didn't work. I thought I may have blown some circuit part in blower motor, not knowing whether I can apply full battery voltage to blower. So, I was puzzled and thought I blew motor.

Not knowing any other possible remedy, I just reconnected resistor assembly and blower motor connectors (without actually mounting assembly) to see if it works. To my surprise, with the ignition switch on and motor speed switch on maximum speed, blower motor worked like champ. I verified this multiple times and it worked every time. So, I mounted both assembly and restored to its original condition.

I am puzzled, what made it work this time. May be electric contact? intermediate part failure in blower motor? I cannot point to a specific thing that made it work.

I am writing this in detail and hopefully it may help someone. It was a very good experience. The blower motor now works consistently so far, and I will keep my finger cross.

Again, thanks to all the experts who share their knowledge to DIY community.

Good find.

You are welcome.

Always glad to help.

Roy