I just bought this 1998 MB C280. 87k, had no problems driving it home for 1,500 miles in two days. After getting home, on the next day, the A/C compressor would try to come on, but would be shut off after 2-3 seconds (observed). It did this routine non-stop. It was 98-100 degrees outside. A/C worked, but since the compressor wasn't allowed to run properly, the air was just cool. Afraid of damage to the compressor clutch, I drove in EC mode. HOT...

When temps fell to higher 80s tonight, I tried running it again. The compressor is allowed to run, and the A/C and climate controls are running fine... BUT both of the condenser fans are coming on as soon as I turn A/C on, and they run non-stop at max rpms. Doesn't matter if I drive or idle. I can't afford dealer, since I just bought the car. Please help!

Found a thread about climate control diagnostic tool. Anyone has meanings for ALL of those sensor Values for this car? Also, I've found and cleared the following error codes: 232, 416, 417, 419. They were in the occasional category. No Continuous errors. Please help me figure out what's going on. Fans should not stay on like that. What are they trying to cool??? My coolant temp is just fine.

Is there a sensor in the condenser that's whacky? Why else would it try to cool it so hard? And what was that deal with compressor toggle? For two days now it's only the fan issue. Thank you all!

P.S. One of the error codes is about a freon pressure sensor... But I can't even check pressure, becasue I don't know which of the values in sensor readings is freon pressure. The only one I'm sure about is 05, which is evap. temp, and it's 38F, which means A/C works.

I am not familiar with this car but is there a coolant temp sensor for the a/c system ? I am basing the following based on my 87, 260E.

The same component (coolant temp sensor), but a different switch within it, is also likely to control the aux fan. Because your fans are coming on right away when you start the car, it tells me that the a/c relay is getting a temp signal that is indicating a hot engine, this cuts off the compressor and turns on the aux fan. If coolant sensor is the problem, then disconnecting the sensor should keep the compressor running. Try this. You may have a 4 pin sensor, 2 pins for the a/c relay and 2 pins for the aux fan relay. If you disconnect all, and the compressor comes on and the fans go off (do this test when the engine is cold), then you found your problem.

Another signal that cuts off the compressor after 2 to 3 seconds of its start is a compressor speed sensor. The coil resistance for this sensor is between 550 and 650 ohms. And when on idle, the sensor should produce around 0.3V AC.

__________________
Saumil S. Patel

I don't know if the speed sensor was retained to that year, but his car does not have any switches in the AC system. The pressure and temperature senders are transducers which communicate to the pushbutton unit.

Don't disconnect the sending unit. This is unlikely to help.

I think that #7 is the high pressure transducer, just like the E class. Connect a set of gauges to see what kind of pressure you really have on both sides. A non-functioning (closed) expansion valve will give you very high pressure on the high side along with very low pressure on the low side. This will also shut your compressor off very quickly; but it will restart once the pressures stabilize.

Thank you so much for your input!

The final problem after ALL flukes:

1) A/C not on, no problem!

2) As soon as a/c is turned on, the condenser fans turn on, and quickly end up running at max rpms ALL the time (driving, idling)

3) Problem with compressor never returned so far, but we did not have temps over 95, so that's maybe why.


QUESTION:
Will improper pressure in the system cause the ECM to think that condenser is too hot? Is there a temp sensor? Or does it decide on pressure alone?

Please help. Anyone...

I believe that you have both a pressure and temperature sending unit, and either can activate the fan.

Anyone with suggested course of action? Please...

How about this:

Here is the latest. I was not able to get any guages. I did take climate control actual readings off of sensors at different times.

01 In-Car Temp (104)-104-(80F)
02 Outside Temp (95F)-95F-(99F)-goes as high as 145 when stopped and idle
03 Heater Core Temp (88F)-91F-(39F)-37F
05 Evaporator Temp (95F)-95F-(37F)-36F
06 Coolant Temp (82F)-125-(190)-192
07 Refrigerant Pressure (6.8)-7.1-(14.3-17.9)
08 Refrigerant Temp??? (86F)-87F-107-116
09 Temp??? (33F)-32F-(68F)-60F-62F
10 ??? (125)-125-435-420-260-255
20 Aux Fan Control Currnent (00)-00-8.0-3.0-4.0-5.0-6.0
21 Engine RPMS (000)-.7-and so on...
22 Speed kmh (000)-000
23 Speed mph(000)-000, no reading ever
24 ??? (12.3)-14.1-(13.9)
40 ??? (03)-03
41 ??? (03)-03
42 ??? (02)-02
43 Version (6-C)
50 ??? (89F)-93F-41F-37F-39F
51 Climate control SET temp (69F)-LO-60
52 ??? (50F)-50F-82F-75F-62F
54 ??? (OFF)-OFF
First set of readings in () are when the car was off, the following readings after each - are taken after initial take off, and then after driving for a little while.

I assume that refrigerant pressures are line 07 and 24. Look OK to me. Anyone? Is line 08 really a refrigerant temp? Does it look OK?

Can anyone, PLEASE, give me the meaning for ALL the lines. I put this list together from different threads from different models.

I got an error code for outside temp sensor, so I decided to watch it. It appears that the dash thermometer is getting its data from some place else and not from the sensor from line 02. Why I think so? Well, when I stop, or just start the car with AC on, the outside temp is steadily climbing, BUT the dash thermometer is STABLE and shows just one temp, which is outside temp. The line 02 sensor reading can go as high as 145F. As I've figured out, this is what triggers the aux fans. When I start driving again, the temp slowly goes back down, and stops when it matches the dash temp. Aux fans are slowing down with the temp decline, and eventually stop. Again, coolant temp is rock stable throughout the temp jumps of line 02 sensor, so I guess I can rule out the overheating. Two questions:

1) Does dash thermometer have its own sensor, separate from the line 02 sensor?

2) I get climbing outside temp only when I'm stopped. Coolant temp is constant, and the sensor reading matches the dash guage. Does this behavior mean a bad outside temp sensor? And how does it tie in with my original trouble, if it does?


PLEASE, PLEASE HELP!!!!!!!!!!!

No expert on your A/C but #7 is reading 6.8, then climbs and stays between 14.3 and 17.9; those readings are in BAR so that's means it's varying betwwn 210 to 263 psi. Those pressures will turn the fans on and the last reading (17.9) will send it to high speed.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

I am not of great help; MattL is. Get some gauges on it.

#10 should be AC blower speed (in volts).

#24 is battery voltage.

Is there no item #04 on this system? Left side/right side?


08 is higher temp than 05, which means that heat transfer is occurring and AC is trying to cool.

Ideally your actual values would be reported at 1500rpm (stationary) with CCU set on auto and temp set at 72F. Ambient temp ~75-85f. Correct me if I'm wrong guys.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Can you please comment on all this? After another day of driving, I now think that my temp sensor is OK. The refrigerant temp is the one that goes up, and it takes the outside temp with it, probably locted near by. I wish I had the guages, but even if I did, I don't see the usual ports on this car. I always ownes Japanese cars, and high and low pressure ports are in the open. I've looked, and did not find anything on this one.

Can I please get some feedback on the latest.

Thank you all so much!

Please tell me where to find guages, and where to find low & high ports.

hi there!

I'm new to the forum, but well experienced on this issue....not because I know how to fix it unfortunately, but because I have the same issue!!....so if you fix yours, chances are we can try to apply that solution to my car, which happens to be a c280 1998 as well....so let's get started....

the ports are located, one at the front of the engine, next to the condenser, but it is on the front side of the car...the other one is on the line that goes from the inside of the car to the compressor...I will send You an email with the picture if you let me know your address...

ok, I remember something that did not work for me but may work for You...supossely the evaporator temperature sensor should not read more than the heater core temperature, this would cause strees to the n22 (climate control unit) and not knowing what to do, it would shut the compressor off....

read....

http://www.asashop.org/autoinc/jan2006/techtips.htm

have You changed your evaportaor sensor lately?...it is around 40 dollars, and it is worth the try...

Thanks for looking into this, mechefan. My sensors seem to be fine. Did not see any flukes with evap sensor. I constantly look at my readings while driving. I'm pretty sure it's the refrigerant pressure, or the sensors. Nobody else would look into this?