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Old 06-21-2015, 08:40 AM   #1
Joesjunk
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Question about blower motor going to high only when AC is on?

I have a '75 Silverado and when you turn the AC on the blower motor automatically goes to high speed and you can't switch it to any other speed. But the fan speed adjusts normal on all other setting, like vent, heat, and defrost. No matter where the fan switch is when you move the lever to AC, the fan goes to high speed. Any ideas on what's wrong? Thanks
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Old 06-21-2015, 09:50 AM   #2
75gmc454
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Re: Question about blower motor going to high only when AC is on?

I know on both of my 76's they do it on the MAX setting. I guess they figured if you wanted maximum cooling, the fan should be on hi also. On the NORM or non recirc setting the fan works on all speeds. I think in 77 they changed the control unit to allow the fan to work in all speeds on the MAX setting also. I know my 78 does.
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Old 06-21-2015, 01:58 PM   #3
Joesjunk
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Re: Question about blower motor going to high only when AC is on?

My 75 doesn't have a max AC, just AC. They must have started that in '76?
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72 3/4t Custom Deluxe 402/auto 66k Original paint
71 3/4t 4x4 Custom Deluxe 10k original miles Original paint
71 3/4t Cheyenne 402 70k original paint
72 3/4t 4x4 Custom deluxe
72 3/4t 4x4 Custom deluxe 91k original paint
72 Cheyenne/30 Dually
69 Camaro SS396 4-speed
13 GMC 2500HD Duramax I bought new
05 Jeep Wrangler "Willys Edition" 12k miles (I bought new)
85 3/4 ton 4x4 Scottsdale 33k miles original paint
86 1 ton 4x4 SRW Silverado 454 restored
80 1 ton 4x4 SRW Silverado 9,434 original miles!! original paint
95 GMC 1 ton dually 4x4 my dad bought new
95 GMC 3/4 ton 4x4, regular cab 454, 31k original miles
2002 2500HD 4x4 regular cab 6.0L 67k miles
2002 2500HD 4x4 regular cab 8.1L 28k miles
2003 GMC 2500HD 4x4 regular cab Diesel 93k miles

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Old 06-21-2015, 04:22 PM   #4
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Re: Question about blower motor going to high only when AC is on?

Oh yes, sorry I forgot about that. Hmm I know my 73's don't do that??
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Old 06-22-2015, 07:56 AM   #5
skeet85silverado
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Re: Question about blower motor going to high only when AC is on?

I had the same problem in one of my older Chevrolets. Take the level that goes from hot to cold and just move it just a little off of cold. Just a tad bit.
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Old 06-22-2015, 09:09 AM   #6
Joesjunk
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Re: Question about blower motor going to high only when AC is on?

That's interesting, I'll give it a try.
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72 3/4t Custom Deluxe 402/auto 66k Original paint
71 3/4t 4x4 Custom Deluxe 10k original miles Original paint
71 3/4t Cheyenne 402 70k original paint
72 3/4t 4x4 Custom deluxe
72 3/4t 4x4 Custom deluxe 91k original paint
72 Cheyenne/30 Dually
69 Camaro SS396 4-speed
13 GMC 2500HD Duramax I bought new
05 Jeep Wrangler "Willys Edition" 12k miles (I bought new)
85 3/4 ton 4x4 Scottsdale 33k miles original paint
86 1 ton 4x4 SRW Silverado 454 restored
80 1 ton 4x4 SRW Silverado 9,434 original miles!! original paint
95 GMC 1 ton dually 4x4 my dad bought new
95 GMC 3/4 ton 4x4, regular cab 454, 31k original miles
2002 2500HD 4x4 regular cab 6.0L 67k miles
2002 2500HD 4x4 regular cab 8.1L 28k miles
2003 GMC 2500HD 4x4 regular cab Diesel 93k miles

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Old 06-22-2015, 06:47 PM   #7
Joesjunk
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Re: Question about blower motor going to high only when AC is on?

That worked, thanks for the info. I wonder why they were like that?
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72 3/4t Custom Deluxe 402/auto 66k Original paint
71 3/4t 4x4 Custom Deluxe 10k original miles Original paint
71 3/4t Cheyenne 402 70k original paint
72 3/4t 4x4 Custom deluxe
72 3/4t 4x4 Custom deluxe 91k original paint
72 Cheyenne/30 Dually
69 Camaro SS396 4-speed
13 GMC 2500HD Duramax I bought new
05 Jeep Wrangler "Willys Edition" 12k miles (I bought new)
85 3/4 ton 4x4 Scottsdale 33k miles original paint
86 1 ton 4x4 SRW Silverado 454 restored
80 1 ton 4x4 SRW Silverado 9,434 original miles!! original paint
95 GMC 1 ton dually 4x4 my dad bought new
95 GMC 3/4 ton 4x4, regular cab 454, 31k original miles
2002 2500HD 4x4 regular cab 6.0L 67k miles
2002 2500HD 4x4 regular cab 8.1L 28k miles
2003 GMC 2500HD 4x4 regular cab Diesel 93k miles

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