It's cold out and my poor '74 is having a nice intermittent problem of not having enough air coming out of the vents to defrost my windows in the morning as soon as the heater core is hot. Tracing the circuit down, the switch for the fan is fine, but I notice the resistor limits the voltage to the fan when temps get high enough, etc...and figure that's where things aren't jake.

Anyone have an 'updated' work around to the two wire system, or anyone know what resistance range the wires/block runs from cold to hot so I could cannibalize my electronics stash and solder up a 'bypass' so I can get more hot air out of my vents...?!?!?

thanks,

-D.Idiot

This may sound stupid but did you check the hoses for cracks? Mine were broken right at the vents and instead of the air going through the vents it went all over under the dash.

Also make sure the doors in the boxes are opening completely.

You can wire 12v directly to the motor if you want w/o hurting it. Would make for good diagnostics as well.

I might be wrong, but I think the resistor is only in play at low fan speeds.

I would try bench testing the fan motor. Like convert says, that resistor is only there to lower the speed of the motor when you select "low" so if the fan does it regardless of speed setting (I'm unclear if thats what you mean) the brushes could be worn or the armature might be shot. While it's out, may as well throw a known good one in there and see how it does... problem persists, I'd check your power feed, maybe a corroded terminal in the bulkhead?

If you really want to get carried away, you could shoehorn in a heater case out of a mark IV lincoln, theyre thermostatic and everything's automatic

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Is this the original blower motor DI? If it is, 30 years of service has probably worn out the brushed and/or armature as steponme said.

If you have an AVM or DVM you can check the blower motor's wire's resistance. If it is very high (more than a few ohms) I would replace the wires. You should also be able to test the resistance of the switch in different positions, to determine if it has gone south.

I am guessing worn out motor though.

-S/6

New motor last year on this car when the core went south, so I replaced both items at once...

I also have two more known good motors to work with, so I'll pull the box and see what gives.

Thanks,

-D.Idiot