[LPete]

I think the low circuit is hot when either:
a) the master switch is off, or
b) the master switch is on, but the fan switch is is the low position.

It has to be that way, but the diagram of the master switch is a little hard to decipher.

Thanks for the diagram!

Edit: This is just a random thought, but if all this is true (about the gray wire being hot in the wrong position) I wonder if the connector is installed incorrectly (or backwards) on the fan switch, if that's even possible.

[Pepi]

That is how I understood it, I am going to have to check mine out sometime to see if it does that. I wonder why it is in the low circuit when master is off, I mean what is the reasoning behind that?

You still want me to post the diagram for my 73? Just kidding.

I agree with you, that if he is getting power on the grey other than in high postion, sounds like a bad switch...Unless someone has messed with wiring at a connector and wired it wrong.

Glad I was able to find a 75 diagram!

[LPete]

It was called something like "Powerflo Ventilation". GM did that for years and years, I think as more of a marketing tool than anything. It definitely is true -- the blower ran all the time.

Thanks much for your help, Pepi!

[vidguy]

THanks guys. THanks Pepi!
I want to remind you guys that I replaced the Control head with a Newer model so the Switch is a little different.....
I used the correct control head harness and it plugged right into the plug from the Engine Compartment.
Ill compare it to my 75 original harness in an hour or so when I get home and see if there are any differences.
Thanks again...

[Pepi]

Originally Posted by LPete

It was called something like "Powerflo Ventilation". GM did that for years and years, I think as more of a marketing tool than anything. It definitely is true -- the blower ran all the time.

Thanks much for your help, Pepi!

Sounds like a marketing tool, must make the blower motor go out faster, constantly running, and since atleast I know the 73's, are a PIA to get out.

Originally Posted by vidguy

THanks guys. THanks Pepi!
I want to remind you guys that I replaced the Control head with a Newer model so the Switch is a little different.....
I used the correct control head harness and it plugged right into the plug from the Engine Compartment.
Ill compare it to my 75 original harness in an hour or so when I get home and see if there are any differences.
Thanks again...

Glad to help guys. Thanks to you to Lee, you were just as helpfull if not more than I was, with your advice for jumping the relay to check cetain parts of the circuit.

It is great to be able to come to a site like this with a problem, and get helpfull information. Keep us posted as to what you find, and what fixes it!

[vidguy]

That diagram shows that I have a moire or less correct harness. And Lee's help showed that the Relay and such is working as it should..
The difference must be in the power to the HI position in my NEW style A/C control Harness and Control.
I went and carefully inspected the wiring. I now know everything about the 2 versions of the A/C harness and the 2 versions of switches........

I have the original A/C control harness and Control and a spare new style A/C harness and control like the one I put in.
I compared them and checked each style switch with my Ohmmeter. I isolated the point that is always hot on both new and old switches..

I found that on both the Old style (75) like Pepi's diagram and my NEW style (77) harness the wire from the HI position to the Engine harness on the switch is in the same place where the A/C Dash control harness connectes to the A/C engine harness. On the Original 75 its a GREY wire.
On the new 77 its a BLUE wire.
so As soon as I get a Chance, (Sunday due to family stuff tomorrow) I'll check the switch and the harness under the dash to see what happens on HI.

One basic question...
If the relay is getting power from the Alternator... Is the Power that is going to the A/C control in the dash just to trigger the Relay? Why power from 2 sources?
Maybe I really dont understand..

Thanks!

[Pepi]

[QUOTE=

One basic question...
If the relay is getting power from the Alternator... Is the Power that is going to the A/C control in the dash just to trigger the Relay? Why power from 2 sources?
Maybe I really dont understand..

Thanks![/QUOTE]

The power from the alternator, the red 12 gauge, eventually goes to the 12 gauge black/orange going to the motor. Strictly to run the blower motor. That is a big draw, so needs the bigger wire, you don't want that big of wire going through the firewall then the switch and finally to the blower motor. And actually that would be a longer run, so probably even a bigger wire. That is why they use relays, close to the current draw like the blower motor.

[QUOTE= Is the Power that is going to the A/C control in the dash just to trigger the Relay?[/QUOTE]

Yes, that is why on the old 75 style , the gery wire would trigger the relay, and like you noted the new 77 style it is blue.

So some how you need to get that blue wire going to the grey. I can try to look to see if I can find a 77 diagram to see the differences and similarities. Might not be able to do that until Monday though.

[Pepi]

My previous quotes didn't work.

Just to clarify, you are trying to use a control head from a 77 in your 75?
Can you post pics of the front and bach of control head if that is what you are trying to do?

Thanks.

[vidguy]

Lee, Pepi-
Thanks! I cant thank you guys enough..

Pepi, Yes I an putting a 77 into a 75.

I went out this morning and did a little before I have to run.
I hooked up both control units and both harnesses.. and tested...

I was wrong ..

My HI doesnt work on Either the 75 (original) or the 77...I swear it did before... They both work the same:
position 2-3 but no 1 or 4...
If I kinda hold the 75 Switch in between 1-2, I can hear the fan come on low.

I dont "Think" the 77 switch is bad but... it could be..
The 75 switch is older and a bit looser so it could be..

I am thinking it could be the RELAY?? But Lee, didnt your help with the jumping the Grey Red at the Relay prove it "good"?
I have 2 77 switches here. I will verify that both do the same thing.
Also I noted that on both control units, the fan doesnt run no matter the position when the LEVERS are in the MAX AC position. I assume that is also HI speed..
I believe I inspected the wiring long enough to see how the levers, when on MAX AC, switches the fan power to HI.

For now here are some images:







75 switch and what I read with my meter switch on HI Key ON, Lever on VENT



77 Switch on HI, Key ON, Lever on AC Normal


75 Control Head below



77 Control Head below



75 Switch and connector - Below


75 Master Plug - Below.
I found that the Black/Red wire is the Low power that is always on.
On the SLIDE LEVER OFF position it puts power to this.

[Pepi]

You are correct with your power readings from your two control heads, So your switches do seem to be working correctly, I think. We need to go after one problem at a time though. On a 77 control head per the wiring diagram, on HI you should be getting power at the following:

BROWN/WHITE STRIPE=power always, comes from fuse.
ORANGE=If you go to the MAX position, you will get power
GREEN/WHITE STRIPE=appears power going to compressor. I know for 73 the compressor always runs unless I move vent/norm switch to vent.

With all that working, which according to your voltage readings it is, sounds like you have a bad wire going from the recepticle end which plugs into the ones pictured and then goes to resistors and blower relay.

Either check for voltage at the relay on the grey wire with everything connected and turned on, or disconnect connectors and ohm out the grey wire from relay to connector which mates upto the ones pictured.

With Lee having you jumper a wire from RED to GREY, and blower worked, yes relay works.

The other thing you can do is, to the mating connector from one pictured, apply voltage to the grey wire terminal. If wire is good, relay should activate, and blower motor runs on high.

To me it really sounds like a bad grey wire going to relay.

After this, we'll go after the blower not working in other positions.

[Pepi]

I colored some of the wires, because the color call out was not the same as yours.

Again, if PDF picture was better, I'll see what I can do to get the colored one as PDF, other wise I'll get the incorrect wire color call out as a PDF.

[vidguy]

I applied power with the Key ON to the Grey wire in engine harness connector which the under dash A/C harness plugs I pictured connect to. Relay kicks on and Fan comes on HI.. Im going to verify if THAT speed is any faster then the speed on position 3 of 4 (Med-HI) which works anyhow...

OK hooked up the Control head and on position 3 of 4 (med-hi) it sounds just like the straight to the GREY wire speed.
Im going to compare that with jumping the GREY and RED at the Relay, which should be HI as well..

At the Relay jumping RED and GREY sounds exactly like my Position 3 of 4 (Med-Hi)

LPete:
James, 12 v on the gray wire and 12 v to the fan *is* high speed. Are you saying that's how it is in position 3, not "hi"?

Yes Lee.. You were right. So what does that mean...?

[vidguy]

OK. I pulled Resistor and it was in fact broken as pictured. It was just a split. Hard to see. When I touched it to try to bend it a little it snapped apart...
I jumped it with a test lead of a very small gauge and the Fan works on HI... but it is slower then Med HI. It must have to do with the windings and size of the wire that broke, right? How carefully engineered is that "spring"?

Now... can i get a radio shack resistor and solder it on there? What is the value? Or should I just by a reproduction resistor? How can I repair this?

Thanks Guys for helping me figure this out!

[Pepi]

In Lee's post #29, his picture shows resistor values,
A=.15
B=.40
C=.54

You caqn try to measure the resistance of the good ones still, and see if they match, then at least you'll know which one you need.
Ohm out between where the BLACK/ORANGE wire goes and the BLUE/WHITE for A
BLUE/WHITE and BLACK/WHITE for B
and BLACK/WHITE and BLACK/RED for C

I honestly don't know if a resistor from Radio Shack would work or not, I kinda don't see why not. Maybe someone else can chime in on that issue.


edit:
Actually looking at your photo more, it appears as though it is the "B" value resistor that broke, you could actually just ohm out each resistor still there.

[LPete]

Glad you figured it out!

You need the replacement assembly. You won't find a resistor at Radio Shack with the correct value that can handle the kind of current it has to.

[LPete]

One more question (without reading the last few posts): Does it still not work on high? The resistor has nothing to do with high blower. Also, is the gray wire still hot in position "3" -- if it is, the blower's on hi in position 3 and shouldn't be. ??

[vidguy]

Lee, It does work in the HI position if I jump the broken resistor. But it is not blowing as hard as on position 3 of 4 with 4 = HI.
In HI position - GREY is NOT hot on HI at the relay
In Position "3" - GREY IS hot on HI at the relay

[Pepi]

Originally Posted by vidguy

4 = HI.
In HI position - GREY is NOT hot on HI at the relay
In Position "3" - GREY IS hot on HI at the relay

That is not right, it is backwards. Grey should only be hot in position "4" HI.

If i recall correctly, the grey should hook upto the orange wire that you said was hot in the HI position.

[vidguy]

Let me clarify that last statement
in position 3 - GREY wire IS hot at the relay
in position HI - GREY wire is NOT hot at the relay.
I know it sounds backwards..

Here is a pic of the Control plugged into the Connector and a legend as I see it:
engine compartment on left - A/C control Harness on right

GREY ----------------BLUE
BLACK/White---------TAN
BLUE/White----------ORANGE
BLACK/RED-----------BROWN/White
GREEN --------------GREEN

[LPete]

Like Pepi said, it IS backwards. You'll have to find out why.