HVAC

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HVAC

Postby jim327monza » Wed May 20, 2015 7:18 pm

Hi, workin on a 76 factory v8 with factory ac. ( monza) The previous owner hacked the wiring harness to "fix" a blower motor control issue. I have the wiring diagram and can understand most of it . I do have a few questions. Notes referring to V-8 HR or V-8 HM models ? I know the fan runes at full speed at max ac and to use the fan control switch for all other settings . Dose the fan shut off completely when the ac/ heat selector (top lever) is in the OFF position ? I am trying to trace the wires to see what was cut/unhooked and what mite have been the original problem. I need to know what it is supposed to do before I can figure out what it is not doing. I have the factory manual, but it is not clear on the sequence of events. As always thanks in advance for your help .

Jim H
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Re: HVAC

Postby zeke » Thu May 21, 2015 12:57 pm

I believe all GM cars run the fan on low when the ignition is on to ensure cabin air flow. I don't remember what year that was started.
Chris

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Re: HVAC

Postby jim327monza » Mon May 25, 2015 6:36 pm

Chris, Thanks for the reply. AS I move through this I have at least one modification that I dont understand. an extra relay to engage the booster fan. this should engage via the eng themo switch. I have not been able to locate this yet. The wiring diagram indicates a v-8 hr or a v-8hm calif. model. I am working on the assumption that this is a calf. model as I bought it from a dealer in calf. Also no idle stop or choke pull relay. I Don't know if this is the because this is a calf. model or if the mechanic took them off. If he took them off I can't find the connectors. the idle stop/ choke pull off may be related to auto/ manual transmission. I am tracing each wire individually by test meter. As always, all input is welcome!

Thanks , Jim H
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Re: HVAC

Postby zeke » Mon May 25, 2015 6:50 pm

The blower motor receives power through the resistor assembly located in the air box. On high blower speed, it receives power straight through the relay, bypassing the resistors completely.

I believe the idle bump for a/c solenoid is powered off the compressor clutch line.
Chris

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Re: HVAC

Postby Monza Harry » Tue May 26, 2015 11:19 am

"Booster Fan" do you mean the electric pusher fan that came with the A/C V8 cars? That should run anytime the A/C is on I believe. The fan is out in front of the Rad on the passenger side IIRC, and would be wired in to that mess as well. Harry
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Re: HVAC

Postby jim327monza » Tue May 26, 2015 6:43 pm

harry, Yes the booster fan is the fan that sits in front of the rad. According to the wiring diagram, it is controlled by a eng thermo switch. As of yet I have not located this switch. previous owner installed a relay to control fan through pressure cut out switch. Main problem at this point, he hacked into the engine harness feed to power the fan set up (red 10 gauge constant voltage even with ing switch off). Now trying to trace original power source back through fuse block -ign switch to fan control. Once I get the wiring fixed I will start testing components to see what needs to be replaced. To say that the chevy issued wiring diagram is not clear on many points is an understatement!!! I Don't know if the 76 model with the 262 v8 differ from the later 305 models.
Thanks Jim H
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Re: HVAC

Postby jim327monza » Wed May 27, 2015 8:49 pm

Ok, just in from the garage. I found the eng thermo switch. It is in the circuit for the engine over temp circuit. Chris, you are right the blower fan runs as long as the ignition switch is on. the booster fan is engaged through the shut off timer/relay. In a over temp situation, the over temp switch engages the shut off relay and in turn the relay shuts off the compressor and turns on the booster fan. just a few more wires to trace, then on to testing the components.
thanks Jim H.
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