Andre Nagel

My early 1986 Corvette's blower motor only works on high speed. I already replaced the blower motor resistor with a brand new one, and nothing's changed. I then replaced the AC power relay with one off of a 1984 Corvette I'm parting out, and the motor still only works on high.

I took some voltages from the plug that connects to the blower motor resistor with the key in run and the AC selector on vent, and this is what I got:

LO speed:
1.3 V between terminals 1 and 2
.3V between terminals 1 and 3
12V between terminals 1 and 4

Med 1:
12V between 1 and 2
11.8 V between 1 and 3
12V between 1 and 4

Med 2:
12 V between 1 and 2
.3 V between 1 and 3
12 V between 1 and 4

I got these directly across the plug without plugging it into the resistor. Does anyone have an idea what the problem might be, and what else I could test? I'm thinking of pulling the AC selector unit from the 1984 Corvette and trying it.

Cliff Harris

The relay applies 12 volts directly to the blower motor when the fan switch is in the HI position. All other fan switch positions apply voltage through the resistor module.

Plug the connector back into the resistor module and measure the voltage on the dark blue wire (referenced to ground) as you set the fan switch to the various speeds.

The connector should have pin letters molded into it, which is what you should use. I don't know which end you started counting from, so your pin numbers don't mean anything to me.

ccrazor

Here is a drawing you can use, the only reading I see being good (assuming your 1 is A, 2 is C, 3 is D, and B is 4, is the low setting reading of 1-4.. I would check for a short in the control from the high to M1 and M2..

Andre Nagel

I meant the flat relay on the side of the blower motor as in the picture. In the Haynes manual I'm using it's labeled as "AC power relay."

I got 10.84 V between the dark blue wire and ground on LO, 10.95 V on Med 1, and 10.95 V on Med 3.

I can't seem to find any letters on the connector, so I was using the numbers on the resistor itself. I took some pictures and labeled them.

WVZR-1

In your first snapshot the component you've included isn't what you've mentioned. This is from an '86 FSM.







Older just conventional wisdom would be to replace the blower switch which was a service part separately OR in your case you could "borrow" it from your '84 control.

Cliff Harris

That's the ESC (Electronic Spark Control) module. It amplifies the knock sensor output and sends it to the ECM when you get a knock. The ECM responds by retarding the timing to stop the knock.

The relay you're looking for is this silver guy (things changed over the years so yours might not look exactly like this):

PAINTER MAN

I also have an 86 with the same problem. I changed the bias resistor also and got no change. I hope someone can answer this.

Cliff Harris

If you have no blower motor with the lower speed settings the problem has to be in the dark blue wire or the yellow on the right of the first diagram in post #3. It could also be in the relay contacts that connection goes through. Also look for corroded pins in the connectors.

Andre Nagel

UPDATE:

I tried plugging in the blower motor resistor connector and jumping terminal 1 (dark blue wire) to the blower motor, and I got it to work on low, medium, and medium 2, indicating that there's an issue with the wire from the blower motor resistor to the blower motor. I think the issue may be where the wire from the resistor connects to the wire going into the motor. I will update later with what the problem was and a fix.

Andre Nagel

Final update:

I fixed the problem by cutting the dark blue wire coming from pin 1, and splicing/soldering a new wire into it. I then ran this wire around to the wire that goes into the blower motor. I put the wire in flex tubing I got from the hardware store to make a new harness, and then T-spliced the wire from the resistor into the wire connecting to the blower motor. Finally, I taped up the splices, put a crimp cap on the old wire, and zip tied the new flex tube to the main wiring harness to prevent things from wiggling around.

In the future I might clean up the old wire that's hanging around, and trace it to where I assume it originally splices into the wire going to the blower motor. Then I'll either cut it shorter and cap the end, or if it's possible, detach the wire from the splice.





Wires coming out of the resistor.





Wire spliced into the blower motor wire.