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Heater Blower Fan Fix - Only High Speed

Old 10-27-2015, 01:11 PM
Join Date: Dec 2010
Location: Lenexa, KS
Posts: 23
Originally Posted by CG901 View Post
What could explain having the same problem (low speed fan on position 2 and 3, but high speed on 4), then replacing the blower motor resistor with no change? No reason to believe the new part is bad out of the box. No rust or corrosion on the old resistor. All connections are good. Thanks.
2003 F150 XLT 4.6
Look for the Molex plug that plugs in the back side of the blower motor resistor having some carbon on several of the spade lugs which slide onto the terminals on the blower motor resistor connector.

I cleaned mine up, but it acted up again. Found a replacement harness at O'Reilly and it's laying on the front floor board ready to go on. Of course since I plugged/unplugged the existing Molex plug and wiggled it around a bunch it hasn't failed. Go figure.
Old 10-31-2015, 01:05 PM
Junior Member
Join Date: Oct 2015
Posts: 1
blower fire

Originally Posted by DEB View Post
Thanks a lot for the great thread. I had purchased a resistor, turns out it was the wrong one anyway. When I removed the existing one to make sure they ordered the correct one I noticed the burning, (mine was much worse than the pictures). The resister was corroded but still worked so I just rebuilt the connector and it works like a charm. Thanks again I would not have known which wires to pull without the pics.

PS Should Ford not be worried about lawsuits when the vehicles catch fire because of this, mine must have been very close.
My blower started on fire and has then taken out heater core and much of the electrical controls. So it happens.
Old 09-06-2016, 07:11 PM
Junior Member
Join Date: Sep 2016
Posts: 1
Blowwer resistor replacement

Found this thread last Thursday. Ordered the resistor from Rock Auto on faith that it was the problem. It came Saturday. Grabbed a mirror from my daughter's room and changed the resistor. Hooray, I now have multiple speeds. Thanks everybody.
Old 09-07-2016, 11:19 AM
Senior Member
Join Date: Jan 2002
Location: Wilmington,NC
Posts: 4,515
That resistor is such a common failure point that Advance Auto Parts had one in stock when I replaced mine. Easy job to replace.
Old 08-23-2018, 10:46 AM
Junior Member
Join Date: Aug 2018
Posts: 1
Thumbs up Me too

Originally Posted by EVIL_SVT View Post
This thread was the reason I came to F150online! My fan switch only worked on possitions 3 and 4 (if they were numbered that's what they would be). I joined the site, did a search and in seconds I found exactly what I needed to fix my switch. I bought the part yesterday and did the swap in the parking lot of Ford (5 minutes tops) and just like that my heat works like new again. Thanks for the awesome write up and pictures!
Yep, same here. This is most likely a common problem, I assume. Thanks for everyone’s input.

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