Heater blower motor not working

SHIVASUN19

MEMBER
2002 HONDA CIVIC
1.7L
4 CYL
2WD
AUTOMATIC
170,000 MILES

Car listed above is an LX model. Tried to diagnose heater blower motor circuit. The battery supply voltage gets to one of the connector terminals of motor (white/blue wire) when I turn ignition switch on (position II) and with motor speed switch to maximum. So, this rules out fuse and motor relay parts which are in series before battery voltage gets to motor. There is other wire (black/blue color) from motor connector goes to blower motor Resistor connector (4 wire connector). Black wire coming from blower motor resistor connector is ground. To bypass this resistor, I disconnected this 4-wire connector and externally jumpered this two terminals (Black/Blue wire and Black wire). I understand this provides ground to motor 2 pin connector (black/blue wire) completing motor circuit. However, blower does not turn on.
Does this imply blower motor itself is bad? Am I missing any other thing in this blower motor circuit?

3 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

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

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Monday, December 13th, 2021 AT 3:38 PM

SHIVASUN19

MEMBER
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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.

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Monday, December 13th, 2021 AT 5:48 PM

ASEMASTER6371