I have a 1999 gmc jimmy the blower motor will only run on high i have replaced the switch & blower motor

If you run 12 volts to the motor itself is it running at high speed ?

faulty blower motor resistor usually located near blower motor

Lets start at the battery. Disconnect the negative cable then the positive double stacked cables. Is there any corrosion? Check between both positive cables. Scrape clean with wire brush or old knife. Add wheel bearing grease to seal out air & reassemble. That is where the common of both circuits are.

Here is a blower motor simple check list.
Hit the bottom of the blower motor. It's located under glove box. you will need to remove a insulation panel to get to the metal of the motor. Tap it a few times with the fan setting on high & in the vent position with the engine running. Did it start? Then motor brushes are bad & fan motor needs replaced. If fan still does not operate wiggle wiring at the motor and the area of the blower motor resistor that is a few inches away from the motor. Could be a bad connection (usually melted) Then it will need a resistor, new wire harness end and blower motor for a permanent repair.

Chris
ASE Master Certified sense 1979

Hey Robert,it may be your blower motor resister is bad,here's a link on how to replace.here's the resister.

hi,

found this for you..

https://www.2carpros.com/questions/gmc-jimmy-1996-gmc-jimmy-heater-blower-motor-not-working

you need to replace a part called the blower motor resistor. it is located behind the blower motor, it looks like a wide slot inserted into the ductwork, and is retained by 2 screws. very common problem, and available at any parts store. good luck!

If the blower motor only works in high, the blower resistors are most likely burnt out and need to be replaced. It could also be the speed switch but since it works in high also it's unlikely. I'm not sure if that's related to the other problem, but it's certainly possible. I would start there and see where that takes you. They are a dealer only item but should only run about $30.

Yeah if you have to tap on it, then that means the brushes in the motor are worn out and you need to replace it. The blower motor is behind the PCM and Coolant Overflow bottle. If you remove these then it will give you better access to motor. You'll have to cut around housing. There should be a groove already there for you, just make sure you don't cut all the way around it. Once you open it and get the new one installed, you'll have to use caulk to seal where you cut it at.

on these models on the harness that plugs into the fan switch goes bad, I changed the switch and found this harness melted together on my 99 yukon

where is the motor as i think its burnt out.