1978 A/C Blower Motor Switch?

[Garys78T/A]

I am new to this Firebird stuff and exactly what does what! I am restoring the A/C system and have replaced the evaporator box, resistor, relay, heater box restored, and blower motor; I think that about handles it.

I am not running a compressor yet, but I have the ground going to it from the harness dialed in on a chassis ground.

My fan works and has 3 speeds.

My problem is the fan shuts off when I put it on "HI"?

I was told these systems do not have an "OFF" position.

I am unsure if I need to keep searching for the problem of the switch not working correctly or if it is possibly a fusible link that may not let the relay work on the "HI" setting.

Any help would be greatly appreciated. Thank you

 

[Aus78Formula]

The fan not working on high is a wiring issue.

A separate power feed bypasses the resistors and gives a full 12v when selected on high.

It may be an incomplete setup since, on some models, selecting high speed would also run through the Max cooling AC setting.

Do you have a workshop manual or wiring diagram?

Possibly also a faulty switch on that speed, but not the usual issues.

 

[Garys78T/A]

I will check that the relay is not inhibited by power.

I'm still curious if the switch is supposed to completely stop the blower motor from running.

Do you know?

 

[Aus78Formula]

In the simplified color diagram, we can see the high-speed setting is full power direct to relay, with no resistors to limit before the fan.

Check the plugs, and maybe get a test light to see if power is getting to the relay on that wire or out of the switch.

It could be a faulty relay, too.

There is no off switch for the fan; it runs continuously.

There hasn't been an offsetting since about 72, and with non-AC, all models with AC.

 

[Garys78T/A]

Thank you, thank you.

I am slowly figuring this out with the help of you and others.

My engine harness was the key to powering my high-speed blower switch.

Since I don't have a compressor to look at, I am trying to figure out which harness I will need to jump power from the engine harness to the AC harness high-speed blower.

As for now, I jumped it with a temporary wire, and it works; yay!

I will not run any of the idle solenoids on my carburetor.

I can't find enough good pictures from the aftermarket companies to decipher what I need.

Thanks again!!

 

[Aus78Formula]

Do you have any 78 Manuals and Diagrams?

 

[Garys78T/A]

Actually, I do.

I found the 1B-5 you sent the other day in the book.

My engine harness has the 10 ga.

Red wire tied with a 16 ga.

Brown wire in the same connector.

I see the 10 ga.

Makes its way over to the Hi Blower Feed.

I can't find where the Brn wire goes, and the jumper harnesses I see online don't seem to have the right opposite side connector of mine.

I'm assuming the Brn wire may be a carb.

Solenoid wire, which I will not be using anyway.

Thanks!

 

[Aus78Formula]

That diagram would likely be B+W in your manual.

The one I had was recolored.

Often, the other way around is to use color diagrams in books but B+W when they sell on CD, etc.

Not sure what your harness is from or to suit, but the side-by-side terminals may be to suit a thermostatic switch, basically a temperature-sensing wick that pokes into the evaporator case to shut off when too cold.

A dual-operating hi-lo pressure switch will replace this altogether.

Jump the terminals and seal if that's what it is. Mid-78 did away with that version.

Depending on features and engine, there are a few variations in the primary AC harness.

Mine is entirely custom, so there's no point sharing pics.

I've also thrown in the harness at AC/heater controls and the small loom at the compressor, carb idle solenoid, ground to compressor bracket, and main connector to AC harness.

 

[Garys78T/A]

The AC main harness seems to be dialed. I do have the temperature-sensing wick you mentioned and it shows it is hooked up to the American Autowire wiring harness.

I have an email to M&H on this issue because I am using their engine harness.

Thank you again for taking the time and helping me sort this out. I'm getting closer.

All the pics above look like what I have cleaned, restored, or replaced.

 

[Garys78T/A]

Well, M&H called me and helped me sort this out.

Their engine harness had two provisions for the alternator, a single wire, and a plug.

The plug I sent a pic of was the other alt. wire, and underneath it lay a green wire, a clear connector with a male spade.

Wa la!

It is the elusive fusible link I was searching for, and I was told that they must have run out of red and substituted green wire figures.

That was not helpful, but moving on.

They had the harness I needed, and it's on its way.

Thanks again for all of your help!!