Blower HVAC Questions

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Blower HVAC Questions

Postby 74_Vega_GT » Tue Jul 21, 2020 6:16 pm

~ Referring to the sticky post on Blower Schematic and HVAC Operation
The writeup is nice and thank you Zeke for that. Concerning the tests as outlined...
~If motor runs, check for power at fuse block and at brown wire on the 3 pin connector behind dash.
~~Can this test be performed with the GT dash harness connector unplugged?---ANSWER-YES The 77 Sunbird w/AC, a 4 speed fan selector has a pigtail with one brown wire and the molded connector does indeed fit the 74 vega gt AC ,3pin connector which eminates from a part of the 74 dash harness, of which you speak. I got no power there with the fusebox hot, hence no low speed fan with key on.
Next check for power at the fan selector switch and then the output of it......nothing there either...

The fan selector switch is a common issue and can be dissassembled to clean the contacts.

The resistor pack does not usually go bad. Check for power in and out.

If the fan works on all lower speeds but no high speed, the relay has probably failed. Relay is located on air box under hood or on inner fender. Check for power on the orange coil wire with fan switch in high position. Check for ground on black coil wire. Check for battery power on the red wire. The fusible link at the starter is a common problem and should be replaced with the proper fuse link wire if found to be open or corroded.
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1974 Chevy Vega GT Hatchback
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