W126 Climate control woes

I’ve been fighting with the W126 Climate Control system for the last few months – and it’s been winning.    When I purchased the car in November last year, it was a very hot day and the A/C worked great.   It had a new radiator, so I took the evidence of leaking coolant to be history rather than a current problem.   Turned out the water pump was leaking and over the next 3 months that leak got worse.   My theory is that the leaking coolant shorted out the compressor clutch,  as it stopped working around the same time.

I was able to check this by bypassing the Klima relay, and the compressor popped the fuse even when the engine was not running.   This did not happen when the compressor was disconnected.

I have since sourced a new compressor which will go on in November when the car goes for its rego.

The blower motor was also very noisy and would turn on and off on its own.   I first thought the issue was with the aspirator fan, which is a small fan to blow air over the temperature sensor.   These are known to get very noisy with age.   Only problem was somebody had completely removed this fan from my car.      Next, I was able to determine that the main blower fan was the problem.     These are still available for a reasonable price, unlike the 107 fan that took me years to find one that was not seriously overpriced.    The one I got was for a left hand drive car (they are different in the 126), but this is not a problem as the plastic housing can be re-used and the actual fan that wears out is the same.

W126 Blower Motors

The blower was refitted and didn’t work.   Next step was to test both motors on a spare battery.   When connected up to 12 volts both motors worked well, although the old was was noisy as expected.    Next step was to check if the motor was getting voltage, and it was. Blower Voltage

This meant that either the resistor that controls the blower speed, or the climate control unit itself were not working.   The resistor can be seen in the photo above and is known as the porcupine.   The blower is fed 12v through a dedicated, high amperage fuse.   The CCU supplies a current to tell the porcupine how fast to run the blower.   I wasn’t able to detect that control voltage from either of the two CCUs I have.  This may have led to trying another CCU, but I decided to change the porcupine first.  They are much cheaper than CCUs and known to fail.     Now I have two porcupines, two CCUs and still not even a working blower motor, let alone working climate control.

I did manage to find a company that offers rebuilt CCUs at a much more reasonable price than the main parts supplier (and looking at the pictures, seems to be the source of their inventory).   I have ordered one of those, and hopefully it will at least get the system and working, ready for the new compressor.  They suggest some checks on the resistance values from the monovalve and Aux water pump. Finally some good news, they are working as expected.

(Update: October 27, 2017 – The blower motor issues were fixed with an updated CCU/Porcupine)

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