HELP! aux fan won't turn off!
 

I got home tonight from about a 20 mile highway drive. when I got into the driveway I was suprised to hear the fan running. I ran for about 30 minutes. I went out to start the car up (I was worried about batter drain). It cranked over real hard. Batter yis definately under some stress. I took off the battery until the car coooled down. Hooked up the batter and the damn thing is still going. I assume the temp switch went bad. The temp guage was barely at 90 degrees! Problem is... I have no idea where it is. I tried taking out the fuse labels as aux fan. No good. It still runs as soon as the batter is hooked back up. What can I do to get this thing to turn off. I have a flight in the morning. I need to get this car back on the road TONIGHT! Thanks in advance!

What year & model??? Can't tell from picture & MB has many different fan control systems!

Sorry. I thought that info was in my sig line. It is a 1991 300E 3.0. also assuming that the fault lies in either a temp sensor or a relay, would these part be available from an 87 190E? When I get back in town I am going to look at one locally that is being parted out. I figure if the parts are interchangeable, I could be back on the road soon. I managed to push the car out of the way and get my other car out. I will look into trouble shooting it when I get home Tuesday afternoon. I just am not sure exactly what I am looking for. some pics would be extremely helpful.

Relay is probably stuck, but I don't know which one it is off the top of my head. Easy way to check is to start pulling the small ones in the fuse box. When the fan quits, you have the correct relay!

Is it high or low speed? High speed is the engine temp sensor, low speed is the pressure switch on the AC receiver/dryer -- check that the wires aren't shorted.

Peter

The fan was going at high speed. As far as the location... HUH? Sorry, you are dealing with a chick here. I usually don't have a lot of knowledge of the internals of my engines until something goes wrong and I am forced to learn. Unfortnately I have not ever run into any sort of an AC problem. What is this dryer you speak of? a physical description would help me out alot. Maybe some sort of general area to look. (good example: the radiator is the metal mesh looking thing about the size and shape of a large pizza box. you can find the radiator infront of the cooling fan and behind the fan that won't quit running. Again I appologize for my newbieness. I am getting there. I at least have an idea of why the fan is running. Thanks for the reply.

Fuse box is right beside the brake booster, under the hood next to the fender, driver's side. One wire spring clip holds it closed. Under the cover are the fuses and about six sheet metal or plastic square or rectangular boxes that plug into the base. These are the relays -- a solenoid operated by a small switch (temp sensor, AC pressure switch). The solenoid pulls a contactor together that switches something with high current draw (like the cooling fan or the electric windows) that would burn up the switch in short order.

Yours is stuck down, causing the fan to run all the time. The power to the swtich is shut off by the ignition switch, so it's a stuck relay.

Thumping on them with a screwdriver handle will often make them let go, but you need to replace the bad one anyway, as it will certainly stick again. Big hassle having to disconnect the battery at a fancy party in a cocktail dress and heels, I'm sure!

Peter