1977 A/C Wiring Question

[AJ 3]

I have a orange wire coming from my vacuum selector switch behind my heating and a/c controls. On my 1977 Crew Cab. The wire it's self is about 6 inches long and has a black plastic female connector on the end. Does anyone know where the wire needs to go?

Thanks

 

[75gmck25]

That should be the wire on the controls that turns on the high speed blower relay. It has power if the A/C is set on max or the fan speed is on high. On the lower speeds the the power for the blower runs through the A/C controls and the blower resistor pack, but on high speed the power for the blower is a direct 12 volt feed from the battery.

I've never traced the wire from the controls, but it should run through the firewall and then over to the blower relay that is mounted on the A/C plenum under the hood.
- When the blower switch is set to high, that wire activates the blower relay,
- The relay then connects the blower motor directly to 12 volts.
- The 12 volt power feed to the relay is an orange wire that runs from the junction near the brake booster, directly across the firewall (with a fuse in the middle) over to the relay.

Bruce

 

[AJ 3]

I have a orange wire that is part or the wiring harness that plugs into the back of the fan switch. It's the other little orange wire just laying in the picture. The other end runs into the vacuum piece.

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[CSFJ]

Illumination for the control panel? I know the factory used orange for a lot of the interior stuff, and I don't see a socket on the passenger side of your hvac control.

 

[AJ 3]

CSFJ the illumination light is there and connected up I just removed so the assembly could pull out farther.

75gmck25 I think you are correct I checked the voltage and when I slide the selector to Max A/C I get 12 volts from the wire.

I still can't find the male terminal anywhere for it to connect to.

I my spare heater selector that I pulled from a different 77 with A/C the fan switch has 5 terminals but the fan switch in the picture only has 4 terminals.

Do I need the switch with 5 terminals so the orange wire can connect to the fifth terminal on the fan switch?

 

[gmachinz]

I am pretty sure that wire goes to your heater fuse at the fuse panel-do you have another wire poking out through your main dash harness with a male 56-series connector on it?

 

[gmachinz]

These older trucks dont have an "off" position-they always have power going to the blower motor even on very low-underhood there should be an ambient temp switch (ranco) that remains open under all conditions where outside temps are 36 degrees or colder. Warmer than that the switch contacts inside close. Its a safety thing for the AC compressor.

But iirc that orange wire has a mate going to the heater fuse-may even be a brown wire too.

 

[gmachinz]

Ok-just checked out my diagrams for 1977 and that orange does indeed go from the selector switch to the blower relay. Its a 14ga solid orange wire.

 

[AJ 3]

According to the wiring diagram I found on this forum. I believe my orange wire is from the Recuc Over Ride Switch and goes nowhere.

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All of my wiring looks intact and I can't find the male connecting end. So I will just leave it loose for now.

Thanks

 

[chengny]

That branch circuit is only used when a rear/overhead system (i.e. RPO C-69) is installed.

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