W126 A/C almost blowing cold

My fight with the W126 Air Conditioning system is almost over.   When I purchased the car, the A/C worked rather well.   After the water pump gave out, it looks like it shorted out the compressor clutch.   Changing out the clutch is not much different to changing out the whole compressor, so I sourced a new compressor and receiver/drier.   This was rather irritating as working air conditioning was factored into the price I paid for the car.

I went through the entire climate control system of the car as part of my troubleshooting.   I found that the car had a missing aspirator fan, a very noisy blower motor, and an intermittent climate control unit.   These were all changed.   The next step was to take the car to my mechanic to fit the new compressor and receiver/drier.  During the disassembly he noticed that the large A/C hose was slightly weeping.  Changing this hose means removing the compressor, so now was the time to do it.   Of course, it is not your regular A/C hose.  It also functions as a way of cooling the petrol going into the fuel distributor.

The hose was sent off to be repaired, as purchasing this hose new from Mercedes-Benz would probably require giving up your first born child.  This involved leveraging the fittings with new A/C hose.    Interestingly enough, while the hose was being rebuilt, I was driving the car around without this cooling function and didn’t notice any adverse effects.

Sourcing the A/C compressor was not as simple as you might think.   The electronic parts catalog calls for part number A0002302411 for cars equipped with self-leveling rear suspension.  As an Australian delivered car, mine is so equipped.   This translates to a Denso 10P15C.    Cars without self-leveling rear suspension require A0002301111 which is a Denso 10PA17C.  These compressors do not look alike, to the point where it looks unlikely that the wrong compressor would fit without modification.   The 10PA17C is cheaper than the 10P15C.

Today, the new compressor was fitted, along with the new receiver/drier and the car gassed up and ready to go.   When the compressor clutch went out, it shorted out the Klima relay, so this is the final thing that must be replaced.   The A/C does work when the relay is jumped.

At the same time, I had been smelling petrol when starting the car.  Turns out the fuel pressure regulator was faulty and was squirting extra fuel on startup.   Apparently to stop petrol leaking out, this goes into the intake.   Changing the regulator is likely to improve the fuel economy of the car.

This has been a rather expensive exercise, but so long as I am not hit by an inattentive SUV driver, I should have a reliable W126 daily driver for the long term.   Some of the most likely potential problems have now been sorted out.  This includes rebuilding the climate control, new water pump, head gasket etc.