Another Blower Motor Problem

[EmTwo]

So my heater blower motor on my 1990 C1500 only works in low speed; I am unable to step up to medium or high.  I asked the dealer and he said it could either be the resistor, or the control panel on the dash.  And that of course, I would need to bring the truck in to have it diagnosed as to which is failing.

 

Any hints on how to determine which?  

 

Thanks in Advance,

[TomEllis]

If you have a volt meter or a test light then you can figure out which it is.

At the blower motor you should have a four pin plug. One of the pins is for the ground and the rest are for the different speed settings. If you do not have 4 pins, but 3 that is ok. They are using the case for the ground.

Put the meter (or light) positive on one of the pins and turn on your blower motor speed control until you get an indication.

check each pin in this fashion. Each pin should give a voltage indication when you put the speed control on the setting for that pin. The only pin that will not give a voltage indication would be the ground pin.

If you do NOT get a voltage indication on any pins when the speed control is in the medium or high position, then you have a bad speed control switch. If you get voltage on the pin for the medium and high speed controls and do NOT get the fan to spin, then you have a bad resistor.

 

I hope this helps you.

Tom