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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: sedavis1974 on August 21, 2014, 10:30:02 pm

Title: 78 chevy blower motor
Post by: sedavis1974 on August 21, 2014, 10:30:02 pm

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

Title: Re: 78 chevy blower motor
Post by: LTZ C20 on August 22, 2014, 01:06:20 am

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.

Title: Re: 78 chevy blower motor
Post by: Irish_Alley on August 22, 2014, 04:40:10 am

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

Title: Re: 78 chevy blower motor
Post by: sedavis1974 on August 22, 2014, 05:56:55 am

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.

Title: Re: 78 chevy blower motor
Post by: bake74 on August 22, 2014, 07:08:55 am

Quote from: sedavis1974 on August 22, 2014, 05:56:55 am

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 (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_78_1978_Chevrolet_Light_Truck_Service_Manual.pdf) 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.

Title: Re: 78 chevy blower motor
Post by: sedavis1974 on August 22, 2014, 07:13:32 am

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

Title: Re: 78 chevy blower motor
Post by: bake74 on August 22, 2014, 07:16:41 am

Quote from: sedavis1974 on August 22, 2014, 07:13:32 am

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.

Title: Re: 78 chevy blower motor
Post by: sedavis1974 on August 22, 2014, 07:19:01 am

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

Title: Re: 78 chevy blower motor
Post by: bake74 on August 22, 2014, 07:31:55 am

Quote from: sedavis1974 on August 22, 2014, 07:19:01 am

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.

Title: Re: 78 chevy blower motor
Post by: sedavis1974 on August 22, 2014, 07:35:04 am

Thanks again

Title: Re: 78 chevy blower motor
Post by: LTZ C20 on August 22, 2014, 08:10:11 pm

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.

Title: Re: 78 chevy blower motor
Post by: 78BIG-TEN on August 24, 2014, 03:30:17 pm

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