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Old 05-08-2021, 08:42 AM
SD455DJ SD455DJ is offline
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Default No Power to Heater Blower/fan

I have a '71 GT-37 that I removed the A/C system and installed an A/C Delete kit to clean up the underhood environment and remove some weight. The replacement 'box' for the AC suitcase is fiberglass and came with a new blower motor & squirrel-cage fan (properly grounded). We replaced a couple of the original underhood AC related electrical components with new (the hi-blower relay and thermal resistor block) along with a new (nos) blower switch in the dashboard. The only thing not replaced is the top-of-cowl mounted ambient switch (not available anywhere?). The underdash wiring is original and uncut while the engine harness (for 455HO with stick & A/C) is a new M&H with the 30 amp in-line fuse and all connections connected properly. (The new electrical components can be seen in the running engine picture if you squint hard enough...old stuff in the pic w/o engine in).

Is the ambient switch needed, or can it be bypassed, jumper wired, or eliminated?

The fuse in the fuse box is good...I didn't check to see if there is a fuse in the new engine harness, or if it is, good yet, but assuming it's there and good, what is the proper process of elimination you would go through to get the blower working?

Thanks much! Dennis
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  #2  
Old 05-08-2021, 05:47 PM
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johnta1 johnta1 is offline
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There is no ambient thingy in the heater wiring.
Probably need to use a non-AC wiring diagram.


Here is a wiring diagram.




PS:
The fuse holder at the alternator is for the AC clutch unit, not used in the heater setup.
(non-AC)

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  #3  
Old 05-08-2021, 08:15 PM
SD455DJ SD455DJ is offline
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Thanks John! We were wondering about using the non-AC wiring diagram, so somehow we have to determine the commonality between the two. So, the in-line fuse doesn't have any impact on the blower motor operation...which makes sense. obviously there is an open circuit that we have to find. We talked more about it today and are going to try hot wiring the blower switch from the fuse box and using a test light to make sure we are getting juice to the end connections.

Dennis

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Old 05-08-2021, 08:49 PM
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The wiring harness from the inside control switch goes straight to the blower resistor block on the heater box surround.

Check power at the switch inside at dash, should have 12 volts (or light comes on in test light) at the brown wire that comes from fuse box to switch.

Depending on switch position like low speed, white wire is 12 volts at switch.

If power there, check at the resistor block. The white wire will have 12 volts. The block will convert the voltage to smaller for the fan motor.


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Old 05-08-2021, 08:57 PM
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Quote:
new (nos) blower switch in the dashboard

Was this for non-AC?

About half of the wiring is wrong for the heater. Different colors also.
(if for AC)



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Old 05-08-2021, 09:23 PM
SD455DJ SD455DJ is offline
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John - the new blower switch is for an AC application and the wiring is so much simpler for non-AC for sure. I like your ideas to test the switch and certainly appreciate it! Thanks much!

Dennis

  #7  
Old 05-08-2021, 09:32 PM
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Here's your diagram with parts not needed.




That master switch in the pic will need to be on for any power to go to the fan.
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  #8  
Old 05-08-2021, 10:10 PM
SD455DJ SD455DJ is offline
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That is most helpful John! Thanks for your help...as you can see, Dan and I are not AC guys, so we need guidance from the fantastic PY world knowledge base.

I think in AC cars the fan only runs when the top temp control slider is moved from the off position and then the master switch sends power to the blower switch. I have an extra AC controls that I saw and heard the master switch click when the temp slider was moved all the way to the off position (far left).

Dennis

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