AC Blower possibly has "given up the ghost" and gone to the pearly gates.

Or maybe not...I recently charged up my system, but there must be a slow leak, as the charge has gone down. My blower motor while driving stops once, then restarted later. The next day or so it stopped while I was driving and hasn't re-started since. I switched over to "vent" and tried all 4 fan speed positions. Nothing.

Is there a pressure limit switch that shuts off the blower fan if the system gets too low?

 

Looking at the wiring diagram for my 78, it looks like the blower motor runs mostly independently of the AC system. As long as the switch is to the right of "off", it will go up to any speed above "low". The blower motor should always be running in the low speed as long as the car is switched on - faster if commanded. Putting it in "max" will default to full blower power. Putting it in any other position (other than off) will rely on the selector switch.

I would suspect your motor is on the way out and is stalling, or there is junk in the box that is preventing it from turning.

Good time to upgrade to a C4 fan cage.

 

Check the blower motor's ground wire. It is just screwed onto the motor's flange and often the ground wire loosens and the motor will work now and then; depending on how good the ground is.

 

If it is truly gone I just saw where guys are putting c4 blowers in. Apparently it blows a lot harder and the only thing you have to do is add a spacer. I think the connector is even the same

 

No.

As like in the other posts. you fan is controlled by the switch in your console..BUT...the thermo-resistor part that is screwed tot eh top of your A/c box on the fire wall is what controls the low med and mid med fan settings. The relay is ONLY for high speed fan.

YES...the ground could be disconnected or loose as mentioned previously.

Could be a bad motor....but you can easily test it buy running a 12 volt fused jumper wire to the terminal on the motor and see what it does. And that is making sure that it is grounded.

I am 'on the fence' if putting a C4 fan in place does really any good or not. Due to the spacer being about an inch....that inch spacer is not allowing really any more air into the box. The spacer is right by the fan...blocking air flow for that added inch...and the air box is made to only allow so much air into it due to its width...unlike a C4 box which is made for the wider fan. Stop and think about it.

I have gotten my air flow rating for a 1974 with all new A/C parts and the system being new with a original design blower motor and all ducts were correctly sealed as required. It blows out air like crazy! I am waiting to get a car that will have the same exact thing except for the blower motor 'upgrade' so to speak and see if the air volume actually changes for the better.

DUB

 

C4 with spacer blows a LOT more air, and my '72 being a vert I blocked off the 'fresh air' door, and made it permanent recirc via the right side kick panel, and removed the silly flapper there too....

HUGE airflow increase, some guys that go so far as to pull the casing, can mod the motor mount position to include ALL of the fan in the chamber, and get more YET, but I not bothered.....

 

I have not had time to investigate this, but definitely will check the blower fan. The C4 blower fan sure does sound tempting too. Heck even if the blower is not bad I might do that. Where do you get the spacer?

 

In my 77 the relay is used for both high and for all the lower fan speeds. In one position the relay connects the 12 volt wire to the fan directly (high). In the other position the 12 volts is routed through the resistors via the relay then to the motor via the selector switch.

Have to agree with mrvette here DUB. There is a significant difference in air flow with the C4 fan vs the C3 fan. So much so that I was blowing out old pipe sealing insulation with the force of the air from the C4 fan.
Try it, you'll like it if you live in a climate that needs A/C.
I did have to "reclock" the back of the C4 motor to get the cooling hose to be in right position however.

You make it. I used some OSB boards laminated together to get the 1" and sprayed it with black truck bed liner to water proof it. Others have used cutting board material. What ever you can come up with.

 

REELAV8R,

Thanks for the correction in what I wrote....I wrote it incorrectly....my brain working faster than my fingers typing. I should have wrote that the relay must be working correctly for the high speed fan to work....or something to that effect.

DUB

 

I picked up some plastic sheet from the local tap plastics. Somewhere, I have all the measurements I took (old fan cage vs new, depth of heater box).

 

 

That's what happens to us over the hill types, our brain still works fast, rest of our body, not so much.

 

By the way, I can hear the relay "clicking" when I turn it to high speed, just the blower is still not coming on. Haven't had any time to look at it this week, but since the weekend is here, might take a look. Too hot outside though!! ouch!

 

The blower on my '79 wasn't working at all. Replaced the relay and the resistor and it works now. Was not hard to do at all, I think I spent under $50 for both parts.

 

Follow the relay testing instructions in the picture I posted above and see if it is working properly.

 

If you go to the C4 blower and motor, measure to get the correct thickness for the spacer, 3/4" has worked well for all the ones I have done. Too much distance between the end of the blower wheel and the air inlet will hurt the efficiency, use the spacer thickness to get it as close as you can without it touching.

 

I did this test just now.

-When testing between 65 and 101 there was no continuity (when there should have been) (failed test)

When 12V was applied:

-Testing between 2 and 65 (with 12V applied) there was continuity (OK) (passed test)

-When testing between 65 and 101 there was a slight continuity (gave me some strange readings) (failed test)

New relay time?

Thanks for the help!!!

 

with Willcox.

Using the information provided....you should easily be able to find the problem when you go to high speed.

The clicking you hear is the coil in the relay ( obviously)...but does not matter if you do not have the proper current coming into the the relay connector so the relay can SWITCH to this pwoer and get the fan running on high.

And on another note. When I wrote the 'relay is only for high speed'. I was somewhat correct. AND this is confirmed by even though wires are connected to the relay. The relay has the capability on how it was designed...that the wires from the resistor to the motor are being joined in the relay and thus the relay is NOT requiring the coil to be pulled to make it function. So all fan speeds (excluding high speed) should work and the relay is not being energized. It is simply a connection that GM is going to switch so the high speed will work when requested. When the HIGH speed fan is requested via the blower switch.....that energizes the coil in the relay. Now with the relay being energized... it disconnects the previous circuit connection and now it is switched to the power supply circuit that is coming into the relay connection from the starter wiring area.

So...if you disconnected your relay connector and jumped circuits 65 and 101 in Willcox's schematic...your blower motor would work in all speeds but HIGH.

DUB

 

I tried this jumper just now, doesn't work.

 

Okay.. Run 12 volts direct with a jumper to the power wire terminal on the blower motor... see if the motor blows.

Also.. put the blower in any speed but high and test for voltage on the dark blue wire where it plugs into the relay.. In any speed but high, this wire will have voltage.

If the relay failed the test then I would still replace it.. but we're now looking to see if you have a blower that is operational, and if you have any power getting here.

Post back.

Willcox

Then