Replaced blower motor and refurbished the heater box. All vent and defroster controls work fine but even on high the amout of air doesn't match a new car. Is that customary with these older cars?

 

No. A properly operating Mustang heater on full blast should have your passengers begging for mercy.

 

Are you getting the proper amount of voltage to the blower motor?

 

What's the test for that?

 

Does the instrument cluster voltage regulator have anything to do with that?

 

No. The 3-speed heater blower gets a full 12V to the motor at all times. When the switch activates, it grounds the motor either directly to ground (high) or to two resistors mounted on the heater box, providing medium or low speeds.

 

Well, I get 3 speeds. I replaced the switch, blower motor, and resistor. Just don't get a lot of air thru the defroster or vents. I cleaned out and refurbished everything. Maybe I'll put the old resistor back in and see if that makes any difference.

 

The resistor is not involved with "high".

Do you have that crappy original cardboard plenum?

 

I think the plenum is the black piece that the hoses connect to that go to the defroster? If I'm right it's made of plastic and appears to be fairly new. Still had the price tag on it. If I connect one of the wires coming from the blower in the engine bay to battery (-) and the other wire to battery (+) to see if motor speed is affected, does it matter which wire goes to (+)?

 

Yeah, if you manage to make the blower run backward, it won't work worth a crap. If your new motor is running backward, it would explain a lot.