78 chevy blower motor

[sedavis1974]

The blower motor in my truck has one speed. I just replaced the motor and the resistor.  But, still the same problem.  Please help!!!

[LTZ C20]

Have you checked your dash switch? It possible the fan selector switch isn't making good contact. A: it's worn, broken bent etc. B: it could have failed electrically. Might be time for a new one.

Also be sure to check you have power and ground going to both the resistor and blower motor.

[Irish_Alley]

like ltz said your truck comes stock running on low to keep the air moving i guess. does it do this or what speed is working

[sedavis1974]

I replaced the selector switch as well. I replaced all 3 pieces because it was only blowing on low. I even ran a direct line to battery ground to the blower. I'm lost on where to go next.

[bake74]

I replaced the selector switch as well. I replaced all 3 pieces because it was only blowing on low. I even ran a direct line to battery ground to the blower. I'm lost on where to go next.

     Did you go through the 78 manual in the tech section ?
     Section 1A-1 (page 35).  Your controller is controlled by cables.  When you replaced the switch, did you make sure your cables were hooked back up and stayed hooked up ?
     I would start there and make sure everything is moving smoothly.
     1A-6 (page 40) has a diagnosis diagram top left corner for testing certain speeds not working.  1A-7 (page 40) has the wiring diagram for each speed so you can check to see if it is electrical.
     Good hunting and reading.

[sedavis1974]

Yeah I checked the cable.  It was doing this b4 I replaced everything. Glad it's summer still

[bake74]

Yeah I checked the cable.  It was doing this b4 I replaced everything. Glad it's summer still

     You are going to have to go through the electrical wiring and check as I described in my last post.  See the link for the manual.

[sedavis1974]

Thanks. I seen something about a high speed relay during my online searching.  Do u know anything about that?

[bake74]

Thanks. I seen something about a high speed relay during my online searching.  Do u know anything about that?

     The manual says nothing about a high speed relay, look through the manual in the tech section, it will give you step by step instructions on how to troubleshoot and diagnose your problem.

[sedavis1974]

Thanks again

[LTZ C20]

I think a good idea would be to make sure you have power and ground going to the entire HVAC system and that the HVAC fuse isn't blown. Not sure if there are 1 or 2 fuses. I think 1.

[78BIG-TEN]

I would check the high speed relay mounted on evep case next to blower,assuming you have a\c of course