A/c Woes
 

This weekend it rained like a mother and i got caught in it in my 86 420sel. Water got the engine all wet and I had turned off the a/c which was blowing cold. I noticed my aux fan was blowing with the a/c off and my temps were only at 80c. I shut the car off and came back about four hours later and the aux fan turns on with the ignition and the a/c off. Now the compressor won't kick on. I drove it about 20 miles highway and still didn't turn on. As i pulled into my parking spot I turned it on and the compressor worked, so I turned it off and went to bed. This morning when I turned the car on the aux fan kicked on right away but the compressor would not. Anyone have any ideas why my compressor wont work after it got wet?

find the a/c relay under hood in front of w/shield next to fp relay.pull it out and find pins #15 and #87[should be next to each other] use needle nose pliers to join the two pins and see if comp starts.if it does we need to look at the other inputs.

The correlation between aux fan staying on and the a/c compressor not coming on points to the temperature sensor. It may be intermittent and ready to fail, or there is just some water in the connector. On my 87, 260E it is the second last sensor on the engine, towards the windhield. Disconnect this connector and see if the a/c starts.

I believe disconnecting the sensor will start the fans and shut down the compressor.

On my 87 260E, the temperature switch closes at temp > 105 degC, and this closed switch causes the relay unit to cut off the compressor. Closing the switch grounds the compressor relay unit's pin 12. My sensor has 3 pins, and two switches in the same part. The other switch is for the blower, and that too closes but at 115 degC to start the fan.

So I am assuming that this is the same for the car here.

I had a similar problem, and disconnecting the connector from the sensor got the compressor running.

It worked when i jumped the pins. Does that mean the klima is bad or something else?

Not yet, could be sensors feeding into the Klima relay. Most likely it is the temperature sensor. The Klima relay unit gets a signal from this temperature sensor, it is actually a switch, when the car gets too hot, the switch closes and Klima relay cuts off the compressor. The easiest way to confirm this is to disconnect the cable at the sensor.

Now if your system is same as mine on 87 260E, then look at this thread, I have posted a long step by step method of checking a/c system at the Klima socket.

http://www.peachparts.com/shopforum/showthread.php?t=158591&page=5

<< and two switches in the same part. The other switch is for the blower, and that too closes but at 115 degC to start the fan.
>>

That sw should bring on the fan at 105c and drop the compressor at 115C
They want the fan to come on BEFORE comp gets dropped , not the other way around...that way, the fan can
come On at High Termal Load and get the temps back in check without loosing AC..if the fan can not control the rising temps at 105, then the sw tells the ac system to quit. [ 115C]. The fan gets activated at the lower temp , [ 105C] not the higher [ 115C]...

Yes, that logic makes perfect sense also, but the MB manual shows that compressor switch closes at 105 and fan switch closes at 115. It would only make sense to do this if the purpose to close the fan switch is to increase the speed to cool the engine rather than the condensor. OR there is an error in the manual, testing the sensor could tell.

It is an error in the schematic..

I DISCONNECTED THE TEMP SENSOR AND THE COMPRESSOR KICKED ON. hOW LONG CAN I LEVE THE SENSOR DISCONNECTED?

Great !! You can leave it like this forever, BUT if your car at anypoint is getting into an overheating situation, not having this sensor could cause a temperature runaway. Dont want to ruin your engine for a $30 part.

Thanks for everyones help today. As soon as I can get a new sensor I will. I was getting worried because I just spent a lot of time and quite a bit of money fixing my leak and i don't want to lose my A/C now.

In the meantime, you can just rig a switch in the cabin for the fan until you can get the senor...many guys run a cabin sw all the time for system over-ride..specially guys that tow boats and stuff..you become the sensor..:)
When you see the temps creeping up, you throw the switch...same as the old days when you threw the heater on b/c the engine was getting a little scary on the temp gauge..

On my 87, 260E, I could just disconnect the signal to the Klima. The fan was running all the time because of the sensor failure, kept the engine cool, must be hard on the alternator though.