I had my air conditioning drain plug up and cause condensation to build up in my heater fan motor housing. The moisture caused the fan to no longer run in the lower speeds. It will only run in the #4 High position. Positions 1,2 and 3 are dead. I went down to the blower motor and tested for voltage and only received voltage when the switch was in the #4 position. I then went to the switch and it tests fine per the manual test procedure. My manual doesn't show much more on the electrical side of the heater. Is the something in between that could cause this? Is there a unit or resistor that reduces the voltage for these other positions prior to the motor? Any help would be appreciated.