Bob T

Compressor exploded on me and I had to replace it. In addition to the compressor, I replaced the condenser and expansion valve. Vacuum was pulled and charged. Air temperature from vents is between 30 to 40 degrees. However, when air is on, fan speed is constantly on high. With AC off, fan speed operates as expected. I replaced the ECU with a refurbished unit. Outside air sensor, cooland pressure sensor and evaporate internal sensor were all replaced. Still the fan operates on high speed when AC is on. Pulled codes and have none.

I also performed the AC control unit reset where you hold the recirc and defrost buttons for 7 seconds an then the indicator lights alternatively flash as the system goes through it's routine. The ignition switch is in position 2 when this is performed. However, the alternate light flashing and testing never stops, it seems to repeat. Is this normal? I have waited up to two minutes and the lights continue to flash and stepper motor, etc continues to operate.

I am very puzzled by the constant high fan problem..........

Bob T

Well it seems I found the problem with the ac control unit not resetting properly, I have problems with both footwell stepper motors and/or linkage. Will have to work on that.....

Bob T

The ac cooling fan is a single speed fan as confirmed by the wiring diagrams. The fan is either off or on. Fan will switch on when refrigerant pressure is above 260 or when coolant temperature hits a designated temperature or refrigerant is overcharged. Again this is not a multi speed fan.

RWDlifer

You don't mention what year/model you have, but on my 05 C230 it is a variable speed fan, based on engine cooling or ac demand or both. I have confirmed this with SDS. Even the AC compressor is variable.
On a hot day at initial start, the fan will run at 100% to get the cabin cooled somewhat, the settle at about 40% once the cabin temp is comfortable. The compressor usually runs at about 70%, and has the ability to cut off during hard acceleration or if refrigerant pressure is too low or too high.
Get it hooked up to star, it will tell you exactly what's going on.

Bob T

It is a 2004 C240

tjts1

The cooling fan speed on all w203s is infinitely variable through a pwm controller. The PWM controller is built into the fan shroud.

RWDlifer

OP, turns out that's normal behavior...Fan will run at 100% if the refrigerant pressure is above 20 bar/290 psi regardless of ambient temperature. Between 12 and 20 bar the fan is variable from 20% to 100%. Below 12 bar/175 psi the fan will not engage (note that fan will still operate if needed by engine cooling system)
A/C system pressure tolerance is from 0 to 30 bar/435 psi

Bob T

I replaced the cooling fan, it is quieter and now correctly varies speed.

thanks
bob

Nathan Herr

Can I ask how you remove the condenser on a 2009 Ml350?