HVAC Blower Motors

[John]

In studying the (useless) wiring diagram from SPF, I see there are two alleged HVAC blower motors.

But where is the switch to activate them?

[Jack Houpe]

It's the switch on the dash. It's a very poor design and hopefully the later cars like your have been retrofitted.

[John]

Thanks, Jack.

It took a bit of looking but actually, not too much. My mother used to get pissed at me for the same thing: not seeing what's in front of my eyes. She'd send me to the cellar for something and we'd spend the afternoon yelling at each other. "It's on the middle shelf right in front of you," she'd say.

"No it's not," I'd yell back.

But sure enough. . .

[Alan Watkins]

The author of the manual neglected to mention item 15....

[Daryl Adams]

Originally Posted by P2164

It's the switch on the dash. It's a very poor design and hopefully the later cars like your have been retrofitted.

Speaking of which, Jack, didn't you do something with the switch that boosted the fan output? I'd love to get a few more CFM out of mine.

[Jack Houpe]

Yes my old friend i did, the wiring going to bower motors is to small and the terminals on the dash switch heat up and create resistance further decreasing the performance of the blowers. Another problem on early cars is all the current for the blowers also goes through the key switch. I used a relay controlled by the key switch taking power directly from battery bus to a PWM (pulse width modulator) which is a electronic DC motor speed control. Removed the 3 position switch and replaced it with a variable control. This is my fix but I think SPF also has a fix for the problem. The key switch is only good for 15 amps, if you ever turn your car off and notice the KEY is warm, you need to correct the above problem on early SPF cars. If there any typos I'm on my iPad and it not as easy to use as my computer.

[Alan Watkins]

Originally Posted by P2164

.... Another problem on early cars is all the current for the blowers also goes through the key switch.

There are a couple factory-fixe documents related to the blowers; it's a confusing comedy of errors with one fix undoing the previous one, etc.,. Attached are the related docs. The primary fix does part of what Jack did (i.e. without the cool PWM motor controller) to protect the switch terminals. It involves wiring in a factory-supplied pair of relays so the poor switch isn't trying to power the motors.

So to get them in historical order, first read this:

0601GT Engine Run On.pdf

Then this (which is where the switch overload fix occurs):

0702aGTB HVACBlower Fan Relay Retrofit Supplement.pdf

Then this:

GT40 Fuse 12 Service Bulletin.pdf

Hopefully you come out of that with reliable blower motors that don'e keep you from turning off your engine.

I just remembered: here is my story implementing the primary fix: Notes re SPF Service Bulletin 0702GTB HVAC Blower Fan Relay Retrofit

[Jack Houpe]

My personal thoughts on SPF electrical is one thing but then again if you run a distributor and carb as in the old days your car will be ok, add to it state of the art mechanical and electronics then you have another issue.