Blower motor runs - except when I turn on AC ('72 250)

[rgnprof]

The fan runs fine in the heat mode, but when I turn on the AC - it stops running. The green AC light lights up on the panel, and the changeover switch and vacuum pod on the driver's side (up underneath the steering column) seems to works just fine. I am assuming an electrical issue - but the fuses look good! Any troubleshoting tips? I do have the AC electrical diagrams and I plan to do some more studying tonight...

Thanks, ryan

[Mike D]

The A/C blower is a different motor than the defrost/heat blower. It is the one located in the center console not the unreachable one behind the heater box.

Usually it's the changeover switch. The actual blower motors are pretty robust. Check to see if something is wedged in the "squirrel cage" preventing it from spinning.

[rgnprof]

Am I correct to assume an operational changeover switch, if, when I turn the AC knob on and off, the vacuum operated lever moves up and down? It looks like it is operating correctly to me...

I don't think anything is jamming it up - it doesn't look like it and it doesn't sound like it is trying to run...but I'll double-check.

ryan

[Mike D]

The changeover switches are prone to sticking. With the car running, turn the compressor control to "on". You should hear the vacuum pods activating and you should see the switch actually move. Push the switch with your fingers to make sure it actually "clicks" to the A/C blower position. They are adjustable. They use a "V" shaped clamp of spring metal to hold position. It's not unusual for them to slip on the shaft.

The A/C blower is also run by a different fuse than the heater blower. I believe on your car it is one on the right front firewall with your window fuses.

[rgnprof]

I replaced the 16A fuse, even though it didn't look blown, and that seemed to fix things. Blower is now running - BUT, I have no cool air. I am going to have to check pressures now - and the AC system...

One thing after another when you drive 40 year old cars!