65 Rear blower motor

[Michael G.]

The rear blower motor on my ‘65 flunked PV ‘cause it only had one speed, when it should have had three. Determined to fix it, I did some investigation in old threads and found that the GM wiring diagram for ‘65 is wrong, but the productions cars were actually built in the correct manner.

Since the diagram is wrong, reproduction wiring harnesses made to it are also wrong, with two wires reversed on the rear blower fan resister plug. As such, if you have a repro harness, you will have a one-speed fan unless you reverse those two wires. I have a repro, and my wires were wrong, so I reversed them. No help.

So then I got into it deeper. Apparently, the fan speed is controlled by a four-position switch. Position #1 is “OFF”. Position #2 (low) sends power through two resisters, to the motor, the resisters slow the fan a lot. Position #3 (medium) sends power through only one of those resisters, slowing the fan, but not by as much as did position #2. Position #4 (high) sends power directly to the motor, with no resisters to slow it.

My problem is now that in position #2 (low) (where the power travels through both resisters), the fan barely moves. But it seems to function well in the other two position. I put new resisters in, no help. I tested everything without the switch in the lines, same result.

I’m guessing that something is wrong with the motor, such that it runs Ok when full power is applied, but not as well as expected with low power.

Am I on the right tracK, is this a normal failure mode for electric motors?

Thanks,

[James W.]

Re: 65 Rear blower motor

Have you removed the carpet cover and cleaned the switch contacts?

James

[Michael G.]

[Wes S.]

Re: 65 Rear blower motor

Could be a lubrication issue, too much bearing drag at low speed.

[Gary J.]

Re: 65 Rear blower motor

Is there another fan motor you could try just to make sure that the low speed you have now is just and nothing more?

[Michael G.]

Re: 65 Rear blower motor

The fan spins freely by hand, so I don’t think its a bearing issue.

What I have discovered is that its a crappy design. I’m not sure why GM would have designed the harness such that one speed is so slow as to be essentially useless in moving air.

For that reason I re-wired it such that the “low” speed is significantly faster. To do so, in “low” speed the current now passes only through one of the two resistors present, rather than both. Since the resistors are significantly different in impedance, wiring it such that at “low” speed the current passes through only the high impedance resistor (rather than both resistors, as the factory did it), and that at “medium” speed the current passes through the other (lower impedance) resistor, I get a low speed that actually moves air, but is still about half the speed achieved in the “medium” setting.

All that was necessary was to move several wires around in the dedicated harness, an easy solution. If any one wants to see the harness or a schematic, please let me know.