Priya

When we got my 79 it needed a new blower motor and the A/C was not working. We replaced the blower motor and got the A/C recharged and it worked for a few months with the blower motor blowing very hard on high fan speed. The A/C has stopped blowing cold although my husband says the lines under the hood are still getting cold.

I think something's gone screwy in the A/C controls and there may be a clue as to what went wrong in the fact that the blower motor only blows lightly now even in the high position. The blower fan stopped blowing hard at about the same time the A/C stopped working. Is there something that might be wrong in the A/C controls that would prevent the blower motor from blowing at high speed even though the fan switch is set on high?

silver79

You need a control modulal that is attached on the fire wall, it controls the fan speed.

Priya

Oooo, goody. That sounds like the sort of thing I was thinking might be causing these problems. Thanks.

Easy Mike

Blower motor speed is controlled by a resistor on the evaporator case.
http://www.ecklerscorvette.com/corve...1972-1982.html

Shark Racer

I thought high speed also had an extra component associated with it?

Priya

According to the description at the link if the blower motor resistor is gone the blower will only work on the highest speed. Mine only works on a low speed. When we first put the new blower motor in we were both really impressed with the force with which it blew, its not anywhere close to that now regardless of where you set the fan control so from what I'm reading at the link I don't think its the blower resister

Priya

I thought there was something that turned it from high speed to ultra high speed without touching the fan control when you put the A/C in "max" position or something.

Mashman

With my 72, not sure if yours is the same, setting to max does not change the fan, it sets the air intake to pull from the cabin, and not outside air. It's 'max' cooling because it's cooling already conditioned air from the cabin, and not outside unconditioned air.

Mashman

The resistor lowers the voltage going to the blower for the lower speeds. For the highest speed, power does not go thru the resistor. It goes to a relay. The relay feeds full voltage to the blower. There is a fuse for this full power (for my 72, not sure abot your car) behind the brake master cylinder - it's one of those push/twist/pull types of fuses. If this is blown, you will not have high speed blower. Also, if the relay (on my 72, it's attached to the side of the evaporator) is broken, or the connector came loose, then the blower will not work in high.

Priya

Okay, sounds like some good leads, much appreciated.

KapsSA

Remove the blower relay from the firewall.
Carefully remove the cover.
Run a strip of sandpaper between the contact points.
See if that helps. Worked for me

Priya

Thanks KapsSA.

I was thinking there was something that would tie together the lack of cold air and the blower motor not working on high so Silver79's comment sounded like the sort of thing I was thinking must be wrong but I see it could be that the lack of cold air and the blower motor not working on high are unrelated. I'm still leaning towards it being a control module that affects both as it seems a bit too much of a coincidence that the two problems should appear at the same time.

Shark Racer

I'd really go at the relay first.

These cars aren't very smart at all.

Max shuts off the vents from the outside air, the fans really just get noisier rather than speed up as they're causing a lot more turbulence in the vents.



That diagram shows how fan speed is controlled on a 78; I have no reason to believe it's different in a 79.

Note that it's basically set up so that current for 1 "low" goes through 2 resistors, current for medium goes through 1 resistor, and current for high goes through none.

Priya

Okay, I think I understand that, but I don't see the relay mentioned by Mashman?

0Willcox Corvette

Below is is the high blower relay.. it's mounted on the firewall... the orange wire that runs to it is what controls high speed. Go to the relay and see if the wire is burned... or just loose from the connector.

The resistor in box does just what it is called.. it changes the resistance on the power wire that feeds the blower motor on all speeds but high based on the position of the switch in the heater control. So as you can see from the diagram below, the tan, lt blue and brown wires are input wires to a different position on the resistor.

but if you have the lower speeds then the blower resistor isn't your issue.

I would put the blower in high and then go test the orange wire to at the relay.


http://willcoxcorvette.com/product_i...ducts_id=25652

Here is a simplified schematic of the wiring.



If the ac lines are freezing up there may be too much freon in the system or something else could be wrong. Does the a/c work until the lines freeze up or not at all..

KapsSA

AC relay, the silver box.
It may be installed on the side of that firewall "bulge" or even sideways.

Priya

The A/C worked intermittently for a while and now not at all.

KapsSA, is the A/C relay you show the same thing as the relay for the high speed on the blower, or is it something different?

KapsSA

Same thing.

0Willcox Corvette

You see that orange wire going to the relay.... when the blower motor is on high it should have power on it...

Pull the connector from the relay and test it for power... If you have power on onrange with the switch inside on high, then make sure the connector isn't burned and make sure the wire connection isn't corroded...

Install the connector back on the relay and then go to the blower motor connection and test for power. If you have power there and the blower still isn’t working run a test ground from the blower motor to the engine and see if the motor works.

If not then the motor needs to be replaced.

If you don’t have power there then replace the relay and test again.

Willcox