I recently noticed that the A/C on my 1981 240D wasn’t cooling so well in heavy traffic. On closer inspection, the W123 auxiliary fan was not kicking in at all. This is supposed to kick in when refrigerant temperatures are high to blow air over the condenser. I had a quick look at the wiring diagram to start troubleshooting. On the W123 diesel is...
In January, I’m taking my family to Tasmania on holiday. Instead of renting a car down there, I’m driving down and taking the Spirit of Tasmania. I’ll collect my family from Launceston Airport as they will fly down. Due to the cost of the Spirit of Tasmania, its actually cheaper to do it this way. It works out well, as they are not interested...
A couple of months ago I tried a modification on my 560SEL to trigger the auxiliary cooling fan earlier. The primary reason for this was to provide adequate air flow over the A/C condenser in stop/go traffic. The W126 A/C was designed for R12 refrigerant and is marginal at best with R134A. I used a resistor to trick the fan into running at...
Under normal operation, the auxiliary fan on the M117 engine cuts in at 105C. It can also be triggered by A/C system pressure. These settings work fine to keep the engine at the correct temperature. The challenge is that most of these cars have been converted to R134A refrigerant. R134A is far less efficient than R12. The A/C system in the W126 was designed...
Now we have hit summer here in Sydney, it was apparent that the auxiliary fan was not working. The fan is triggered either by high coolant temperature, or refrigerant pressure. High coolant temperature causes the fan to run at full speed. Refrigerant temperature can trigger a slower fan speed based on a resistor. Before I just jumped into W126 auxiliary fan replacement, I tested...
Once I got the air conditioning working on the 560SEC it was apparent the auxiliary fan was not working. As can be seen in the wiring diagram below, the W126 SEC auxiliary fan can be triggered either by high coolant temperature or by refrigerant pressure. The diagram is for 1986-1990. In 1990, the W126 went to a dual fan setup. The fan can...
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