Heater Blower Problems

[landy]

'72 K5 with factory A/C. The fan switch was broken when I bought the truck, so replaced the switch with a new one from LMC. The blower motor now worked. So onto the A/C. Installed a belt, and the compressor would engage, but the blower motor no longer worked. Well, the system is likely out of refrigerant, so understandable why it doesn't blow cold.

But now the blower motor no longer works at all. There's 12 volts at the brown wire where it comes into the switch. The fan switch has three positions. There's 12 v on the blue wire into the switch at positions 2 and 3, and 0 v in position 1 (the upper position). There's 0 v on the orange wire at all positions. There's 12 v on the yellow wire at positions 2 and 3.

At the wire to the blower motor (in the engine compartment), there's 0 v with the switch in position 1, and only 7 v with the switch in positions 2 and 3. Is there a resistor in the circuit between the switch and the blower motor? My manual seems to suggest that the switch should have four positions, off, lo, med, and hi.

Any thoughts?

Thanks.