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Defrost Setting Question 1987 Z28 4 bbl carb

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Old Jan 6, 2016 | 04:58 PM
  #1  
blascwil's Avatar
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From: Melville, NY
Car: 1987 Z28 coupe-hard top
Engine: 5.0 Ltr/305 ci 4 bbl carb
Transmission: 5 speed manual
Axle/Gears: RWD - Stock gears
Defrost Setting Question 1987 Z28 4 bbl carb

When I set A/C-Heat selector to "Max", "Norm", or "Bi-Level", the AC compressor kicks in, the idle solenoid increases the idle speed and the radiator fan comes on. However, when I set it to "Defrost" only the AC compressor kicks in. The idle speed does not increase and the radiator fan does not come on. Is that normal, or do I have a problem with the selector switch?
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Old Jan 6, 2016 | 06:04 PM
  #2  
rusty vango's Avatar
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From: knoxville tn
Car: 86 IROC
Engine: 5.0 TPI
Transmission: 700-R-4
Axle/Gears: 2.73 open
Re: Defrost Setting Question 1987 Z28 4 bbl carb

thats how its supposed to be
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Old Jan 6, 2016 | 09:02 PM
  #3  
blascwil's Avatar
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Joined: Jan 2016
Posts: 5
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From: Melville, NY
Car: 1987 Z28 coupe-hard top
Engine: 5.0 Ltr/305 ci 4 bbl carb
Transmission: 5 speed manual
Axle/Gears: RWD - Stock gears
Re: Defrost Setting Question 1987 Z28 4 bbl carb

Originally Posted by rusty vango
thats how its supposed to be
OK, Thank you very much.
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Old Jan 7, 2016 | 08:09 AM
  #4  
naf's Avatar
naf
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From: Lexington, SC
Car: 1987 SC/1985 TA
Engine: 350/vortec/fitech
Transmission: T56
Axle/Gears: 3.27 9-bolt
Re: Defrost Setting Question 1987 Z28 4 bbl carb

I'm almost certain the idle bump solenoid and the fan should come on in defrost. I know the bump solenoid does for my 85. It's been too infrequent driving my 87 for me to recall. I could check...

A wiring diagram would show the intended function but some are not to be trusted.
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Old Jan 7, 2016 | 10:50 AM
  #5  
blascwil's Avatar
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Joined: Jan 2016
Posts: 5
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From: Melville, NY
Car: 1987 Z28 coupe-hard top
Engine: 5.0 Ltr/305 ci 4 bbl carb
Transmission: 5 speed manual
Axle/Gears: RWD - Stock gears
Re: Defrost Setting Question 1987 Z28 4 bbl carb

Originally Posted by naf
I'm almost certain the idle bump solenoid and the fan should come on in defrost. I know the bump solenoid does for my 85. It's been too infrequent driving my 87 for me to recall. I could check...

A wiring diagram would show the intended function but some are not to be trusted.
I noticed it in October when I put it on defrost to clear inside windshield fog. At idle, the compressor started groaning and the temperature gauge shot up. I opened the hood and saw that the radiator fan was not on. I switched to A/C Norm and the idle increased, getting rid of the groan and the fan came on and cooled down the engine. I think you're right and I have a problem with the control switch. I will check my Haynes & Chilton wiring diagrams to be sure. Then I will pull out the control assembly and see what I have. Thanks so much for your time.
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