Ac questions

[1979C20]

I have 2 questions. My clutch wont engage when I move my controls. I checked the clutch by jumping it to the battery and it worked. I bought a blower motor relay because I didnt have one previously. I jumped the high side pressure switch/clutch cycling switch and the clutch still did not engage, with the key on and the control set to max ac and cold. when I connected my blower motor relay, I can here a slight hum/whine from the blower motor but.it wont engage on any setting. During the winter I ran a toggle switched power wire to the motor for heat. So my questions are....

Why wont my blower motor engage, and why wont my ac respond to the switch?

Fuses are good, I checked wires and theyre good from what I can see.

[78 Chevyrado]

Checkout your new relay.  Pop the cover off of it and look to see if there's a burnt resistor inside it.  if there is, get another new relay, and cut the resistor out BEFORE you try to use it.

On my 78 I had that problem.  took like 6 new relays to figure it out.  The new Relay was identical inside to the old GM relay EXCEPT that the new one had a resistor in it the old one did not.  everytime I hooked it up and tried it, it fried the resistor instantly and then nothing worked.  I got it figured out and cut the resistor out of the last new relay i got and it works great now, just like it should.

So if possible check out your new parts and compare them to the old stuff.  some  new stuff isn't right.

[1979C20]

I looked in the tech section but I couldnt find a wiring diagram for the AC. Is there one?

[1979C20]

Can you snap a picture of the resister you cut out? Thanks in advanced.

[1979C20]

Bump, really need the help on the ac please. Does the blower motor relay have any role in if the ac clutch engages or not?

[VileZambonie]

I jumped the high side pressure switch

What high side pressure switch? You shouldn't have a high side pressure switch. Is this a factory system?

[1979C20]

The switch on the dryer. I guess its the clutch cycling switch, not the high side pressure. Stock system.

[topp]

You have several issues....
1- you hacked in a switch to your blower and expect us to know how your custom wiring job is laid out... Put the wiring back to waht it was and do some basic electrical troubleshooting- Do you have power to the switch, do you have power to the relay? Do you have power to the resistor? Do you have power to the motor.

2- your stock A/C switch may be shot, along with your stock blower switch.  Jumping the low pressure cut off should have engaged the compressor. 

[1979C20]

I explained already that all I did was run a toggled power wire straight to the purple wire on the harness for the relay, as that is the wire that controls the blower motor. And I also said I connected a relay back to it. Every thing is set up as stock. When I jumped the wires on the switch on the dryer, the clutch didn not engage. How do I check to see if my switches are good or bad?

[VileZambonie]

I explained already that all I did was run a toggled power wire straight to the purple wire on the harness for the relay,

OK ever watch family feud? You know that annoying Red X and the sound it makes? Imagine that right now.

Do it right the first time. Listen to topp when he's given you the correct answer.

[1979C20]

Does anyone have a wiring diagram that shows the ac wiring? I cant find one.

[1979C20]

Never mind, I found this one after hours of searching. http://forum.73-87chevytrucks.com/smforum/index.php?topic=1944.0 im going to pul pull my dash apart and check for power at the wires on the switches and check for power at the wires in the engine bay tomorrow.

[1979C20]

Okay. Ive made some progress. With the pressure switch on the drier jumped and the fan switch on low, key on, ac max the clutch engages. Once I turn the fan switch to high  it blows the ac/heater fuse. The blower motor does not engage with the key on. Any idea why the fan blows the fuse?

[1979C20]

Anybody?

[Irish_Alley]

too much resistance in the fan. does it blow it with just the heater on?