Blower motor or resistor?

[koda2000]

2000 Explorer 5.0L 206K w/manual HVAC controls. I noticed that with the blower on low (with the AC on, or on VENT) the blower motor is changing speed all by itself. it will speed up to maybe the next higher setting and later slow down again. I wouldn't think that a bad ballast resistor would cause this. i'm leaning toward the motor itself. I've never experienced this before and I haven't driven it enough to know if it happens on the higher blower speeds as well. opinions?

 

[J_C]

That is odd. I'd pull the resistor module and inspect it then if it looked okay I'd move on to the motor since the fan is supposed to only run on high if any resistor coil on the module burnt through.

 

[chefduane]

Never heard of something like that. I did have a problem with the motor sometime back just not blowing like it used to and decided to change it out. It was easy enough and I figured that while I had it apart I'd do the resistor also. I think the blower was about $35 and the resistor was $20, and Autozone had the parts in stock. Maybe about 2 hours or so to do it. I destroyed the blower gasket getting it out as it dries and gets cracked over time. It was simple enough to make a new one out of some gasket material I had and seal it in place with some silicone sealant.
This is N. Texas and it gets Texas hot in the summer, and we can see some teens and 20's in the winter. Gotta' have a good blower when needed.

 

[crunchie_frog]

I would think it would be unusual for the motor to run at different speeds if it were getting a constant voltage. Sounds like the resistor, wiring, switch or connector to me.

 

[koda2000]

Thank you both for your input. As this is a spare vehicle at present, I'll just keep and eye/ear on it for now. I'm now curious as to whether this will occur at the higher fan speeds. I guess it might also be the fan switch itself. It's not a big deal as long as the blower motor works.

 

[istroo]

I had a bad ground in my Bronco 2 that caused a similar problem.