Author Topic: 78 chevy blower motor  (Read 6727 times)

Offline sedavis1974

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78 chevy blower motor
« 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!!!

Offline LTZ C20

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Re: 78 chevy blower motor
« Reply #1 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.
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Offline Irish_Alley

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Re: 78 chevy blower motor
« Reply #2 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
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline sedavis1974

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Re: 78 chevy blower motor
« Reply #3 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.

Offline bake74

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Re: 78 chevy blower motor
« Reply #4 on: August 22, 2014, 07:08:55 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 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.
« Last Edit: August 22, 2014, 07:13:53 am by bake74 »
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
  74 k10, 77k10    Tom

Offline sedavis1974

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Re: 78 chevy blower motor
« Reply #5 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

Offline bake74

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Re: 78 chevy blower motor
« Reply #6 on: August 22, 2014, 07:16:41 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.
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
  74 k10, 77k10    Tom

Offline sedavis1974

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Re: 78 chevy blower motor
« Reply #7 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?

Offline bake74

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Re: 78 chevy blower motor
« Reply #8 on: August 22, 2014, 07:31:55 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.
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
  74 k10, 77k10    Tom

Offline sedavis1974

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Re: 78 chevy blower motor
« Reply #9 on: August 22, 2014, 07:35:04 am »
Thanks again

Offline LTZ C20

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Re: 78 chevy blower motor
« Reply #10 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.
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Offline 78BIG-TEN

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Re: 78 chevy blower motor
« Reply #11 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