2001 S80: Diagnosing HVAC Blower System

DanSC · Post by **DanSC** » 20 Jan 2014, 17:40

Hello,

Recently, the HVAC blower on my S80 with automatic climate control quit. I took the motor our per this guide, and the motor turns when connected to the battery. I also checked the fuses and relays mentioned in this thread, and they all seem fine.

Now I am trying to determine if the problem is the regulating resistor or the climate control module. Using page 96 of this PDF wiring diagram and a multimeter, I've found the following voltages:

The voltage for main power supply to the resistor (4/31), between A:2 and A:4, is 11.3V regardless of fan setting.

The voltage from the CCM to the resistor, across A:1 and A:3 on 4/31, is 9V when the fan knob is at any setting other than OFF.

With the fan running I've measured either 11.3V or 0V coming out of the resistor to the motor (6/28). I am not sure of the reason for the discrepancy.

My current thought is to replace the regulating resistor, but I know next to nothing about the CCM in this car. Does any of this information suggest at CCM issue? Any advice would be greatly appreciated.

For what it's worth, I can still hear the motors that redirect air through the various vents move when I adjust the climate control settings, so I don't think the CCM is completely shot.

paulhoward · Post by **paulhoward** » 26 Jan 2014, 12:29

Thanks, I changed out my module with help here.

paulhoward · Post by **paulhoward** » 27 Jan 2014, 09:56

Just a quick note on the CCM's. The system is wired through the Speed Control Module. Mounted on the Blower Motor Housing. If this Module fails, Blower may be Hot or Energized at all times. Thus a drained battery. Or it may fail locked in on a particular speed setting. Or it may fail in the off position. The voltage and current to the Blower will not change based on the switch setting, it's just an adjustable very/very quick on/off switch. The Speed Control Module is what they sometimes call a DC Chopper. It switches the DC current on/off at a very/very fast rate. The more time the current spends in the off position the slower the blower speed.

The CCM only sends a signal to the Speed Control Module to regulate or control the switching speed, based on the fan speed control knob setting. With this type of system, the most common failure mode will be the Speed Control Module.

DanSC · Post by **DanSC** » 25 Feb 2014, 12:51

I replaced the fan resistor, and that solved the problem. Apologies for the delay; I ordered the part on eBay, then realized it would be shipping economy-rate to North America from Bulgaria.