After market heater blower motor wiring

Hey folks, I bought a new heater box blower motor. The old blower had 3 wires, Red, Orange & Black. The new one only has two Orange and Black and they are interchangeable to reverse the fan.

Any cleaver ways to make this a dual-speed blower, or is there a more appropriate replacement that has the 3 wires for dual-speed?

 

Try grounding the blower frame if you haven't done that already. The two wires may be for low speed and high speed.

 

Unfortunately, tried that. The body isn't a ground...

 

Measure the amount of current that the blower draws and find a very low resistance high wattage resistor to match. Put this resistor in series with the mtor when you want it to run at lower speed. IF you could find a rheostat that could handle the wattage/current.... you could have an multi-speed motor.

For specifics on HOW to do this, read a primer on Ohm's law......

 

Not being an EE expert, this is what I think is right. Can you verify that my calculations are right?

The old fan draws 1.7amps on low and 2.2 amps on high. The new fan draws 1.6amps. From my rudimentary Internet readings on OHM’slaw, to achieve the 36% drop in speed I think I need a 2.5 ohm 6w resistor.

 

when current (I) & voltage (E) are known you divide I into E to get Resistance.
When current (I) & voltage (E) are known you multiply E times I to get Power (Watts).

This is the law for DC circuits.