My auxiliary fan would not turn on at low speed. I will use the Climate control diagnostics tomorrow to look at the pressure and temp. I'm trying to locate the ECT and Refrigerant pressure sensor on my C43. If anyone could give me some ideas and how they look, it would be a great help.

Also is there a way to jumper the sensors to see if the auxiliary fans would turn on? High speed activation is okay so I'm more leaning toward either low refrigerant charge or the pressure sensor itself.

Is the pressure intrusive to the AC closed loop system? I need to find out if I need to evacuate it first.

OK, after reading the refrigerant pressure from the climate control codes, even after reaching pressure at 14 bar (low speed should kick in) and up to 17 bar (high speed should kick in), auxiliary fans still did not come on. The auxiliary fan did come on at low speed after eventually reaching the 95 C engine temperature. So, it looks like the problem is not on the engine temperature switch, but on the refrigerant pressure switch.

I tried jumpering the pressure sensor connector (has 3 wires) on the side of the air drier, but the auxiliary fans still would not come on. Does anyone know, which wires to jump and should the connector be back on the pressure sensor?

I'm really thinking that it is the pressure sensor because I've already checked the relay(green) and fuses and they are all okay, but I want to confirm this before purging the system out and the refilling.

Now the auxiliary fan spins at high speed at the setpoint of 17 bar and turns off at 13 bar, but at this time with the outside temp at 95 C, air still does not cool. So basically, I need to find out why the auxiliary fan does not stay on when AC is on. It seems that the refrigerant pressure is okay. I really want to isolate this problem without having to take it to the dealer.

Did C43's come with fan control module? Some people are saying that it could be the problem

Not having a wiring diagram handy I'm straining my brain for fan operation theory when up pops this small seemingly sidebar sentence: "air still does not cool" and I'm sitting here wondering what to talk about.

Just what would you like to achieve with a solution here? Cause if the temperature of your AC has anything to do with it what does the fans have to do with it. Is there too much pressure?

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I'm also trying to figure out the problem. Is the car running too hot? Is the AC not working properly? If memory serves, the aux fans are run by engine coolant temp and AC pressure, but I'm not sure the sequence.

Try pulling the fuses for the instrument panel (19 and 30 on my C230). That kills the coolant temp gauge, and the system no longer reads it. It defaults to 106C, which in my car is the kick-on point for the electric fan on high speed. The fan comes on continously in that condition.

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

Had the same symptoms on the 1997 C230. First state of engine cooling fan would not come on. Suprisingly, the engine never really got too warm, but every time I came to a stop with the ACC cooling, I got warm air blown on me (moving, it blew its normal, ice cold). It ended up by a relay near the engine cooling fan.

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Michael

1988 300 SL (5 Speed)
1994 E320 Wagon
1997 C230