Volvo Repair: 850 T5R Heater Fan, resistor pack, automatic climate control

Question
Hi James,

My heater fan doesn't work at all. The switch cluster is getting power because all of the lights are on. ALso, when I switch the Vent dial- you can feel that the air is diverted to the correct respective setting. All fuses are ok- I checked with a multi-meter. I removed the glove box and had a look at the input connector to the fan- it is definately engaged. I also tried to jump 12VDC to the red wire but I got a small spark so I didn't continue- the fan didn't make any sign of starting up. Is the fan PWM modulated? If so, could there be a problem with the control unit / switch cluster...or could it simply be the fan or slide switch that controls the speed? Your assistance would be appreciated!

Answer
Do you have the automatic climate control or manual control?  

Automatic:  Fan request goes through a relay to the power stage (located in the airducting behind dash) which then controls voltage to the fan.

Manual:  Power goes from a relay to the resistor pack (same position as power stage) which then goes to the fan.

The relays will be right nest to the power stage/resistor pack.

If you can test for power and ground and both show good (when the motor is switched on) then the motor is broke, otherwise you'll have to trace it back to where the open or short is.   The motor is not PWM, it gets a variable voltage which varies the output.  Hope that helps.

James