1997 C230: Air Con Problem, Pls. Help Diagnose - PeachParts Mercedes-Benz Forum

Michael K · #1 08-06-2003, 05:15 PM

Howdy. The climate control cooling function on my 1997 C230 is acting up…

So long as the car is moving, the AC is good and cold like it always was.

However, starting this Summer, when I stop moving for longer than half a minute, (traffic light, major gridlock, etc.) the compressor disengages and the air flowing from the vents gradually gets warmer and warmer. When I start moving, it starts blowing cold.

I’d really appreciate some help.

I’ve searched the forum quite a bit and have just about concluded that the culprit is the evaporator temperature sensor.

So my questions then are first, how to positively test that the evap. temp. sensor is the issue, and second, how to install a new one?

(I’m familiar with pulling the values and codes from the climate control PBU).

Thanks very much in advance. Best regards,

mbdoc · #2 08-06-2003, 05:57 PM

Sounds like the ENGINE cooling fan isn't running fast enough to keep the condenser cool.
There are sensors on the drier that send signals to the A/C pushbutton.

The fan is computer controlled, is it runing at all??

Michael K · #3 08-08-2003, 11:47 AM

Thank you, sir, for your help.

The engine cooling fan IS NOT running.

To clarify, I looked at the engine cooling fan (with the engine running, the temp guague reading about 85, and the A/C set to 72), and the fan is not moving at all. However, today in crazy traffic, the temp guage climbed from about 85 to just over 100. I'm pretty sure I heard the fan come on quite loudly then.

If it's something easy to fix, I'd like to try it myself. However, I'm not adverse to concluding that I can't tackle this problem myself and that I should schedule a service appointment.

Any advise appreciated. Has anyone seen this on the W202 C230?

Thank you. Best,

blackmercedes · #4 08-08-2003, 03:53 PM

On my C230, in summer traffic, AC cold, the electric engine fan runs almost all the time at slow speed. If the coolant reaches 106C, the fan kicks on high (and I mean VERY loud high -- jet enigne whine!). I tested the this by pulling fuses 19 and 30, disabling the coolant sending unit. The car kicks into "emergency" mode, and since it can't see the engine coolant temp, defaults to 106C and engages the fan at high speed.

It sounds like a fan problem, as it should be running at slow speed lots. The fan motor should be fine since it kicks on at 106C, but there is a controller issue somewhere. Also, even in 40C heat with the AC blowing ice cold (evap temp of 6C) my car has not one time kicked the fan to high speed. I've seen coolant temps of 101 or 102, but not 106 even once. If your car is doing that, it convinces me that you've got an engine cooling system problem, not an AC problem. The fan sounds suspect.

Michael K · #5 08-08-2003, 05:21 PM

Hi John,

Thank you. I appreciate your help.

I ran a few tests... there are differences in our fuses

In the main fuse box, my fuse 19 is for "power socket, trunk - station wagon" and there is no fuse 30. So I found:

-fuse 2 for "fanfare, control unti autom. climate control, auxiliary fan control - 4 cyl. engine
-fuse 18 blower control, auxiliary fan control - 6 cyl. engine" (I know mine's a 4 cyl, but it was a close match and there IS a fuse in there)
-fuse 29 for "auxiliary fan - 4 cyl. engine."

First I pulled fuses 2 and 29. The engine started and ran fine, the battery warning idiot light came on, the temperature guage sat at 85, the climate control PBU was completely off (not even displaying "OFF") and the engine cooling fan DID NOT move.

Next I pulled fuses 18 and 29. Same result as the first test except the climate control PBU displayed "OFF," displayed the "72" that I set, and/but the climate control did not start it's fan.

I put the fuses back in, started the engine, then set the climate control to cool to 72. The battery idiot light did not iluminate and the engine cooling fan DID NOT move.

I replaced fuses in question with the spares with the same results.

My goal is to figure out if this is something simple I can replace/fix myself or do I need to take it to the professionals?

Thanks for any help you can offer. I really appeciate it.

Best regards,

blackmercedes · #6 08-08-2003, 06:18 PM

Fuses 19 and 30 on my car control the gauge cluster. By disabling the gauges, the car cannot read the coolant temp and defaults to 106C. Of course, your 97 might be different.

The reason I suspect something with respect to the fan is that my electric fan runs at a slow speed most of the time in the summer. Never looked in the winter.

Without the fan running, you're not pulling enough air through the rad or the condensor.

The evap temp sensor has nothing to do with the movement of the car, and that I would imagine rules it out, as your AC blows cold when the car is moving.

Things are pointing to a fan problem. No slow speed fan engagement would cause the problem set you have.