Heater Blower Motor Diagnostics
If your blower fan is inoperative on your 850 or S/V70 up to 2000, start with the basics and check the fuse.
From there proceed to the blower fan itself located behind the glove box. To access it, remove the Torx 25 screws holding the glove box in place and remove the box. Remove the Torx 25 screw holding in the pass side knee bolster cover and remove the 13mm nuts holding the bolster in place. Position the fan switch to high and turn the key to position 2. Using a test light, probe the large red wire on the two-wire fan connector and look for the test light to glow brightly. Adjust the fan speed and you should see a noticeable change in test light intensity. If your test light responds accordingly, time for blower fan replacement. If you aren’t getting any illumination on your test light you may have a bad final stage or climate module.
The final stage for Electronic Climate Control (ECC) controls the high power current to the blower motor based on the input from the climate control module. For vehicles with manual climate control (MCC) a resistor pack is used. When either ECC or MCC is set on high fan speed and also set to defrost, full current is applied to the blower fan, this can be useful as a diagnostic step to discern between fan or final stage failure. If your ECC has flashing LED’s on startup for around 20-25 seconds you have a code in your system. Many times a ‘high current code’ is set from a blower fan that is going bad and is drawing more current than normal. Depending on how much excess current the blower fan drew the final stage/resistor pack may have been damaged and need replacement.