I replaced the temp sensor about 2 years ago which fixed the same symptoms. I heard clicking relays before the fan stayed on. When I pull the plug off the sensor, the fan stops. Is it the sensor again? Could it be a relay? I find it hard to believe that the sensor is bad already. Any suggestions?

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si

That should be a single wire sensor that trips to ground..Check the sensor
terminal to ground when coolant is cold with an ohm meter.. if you have continuity , the sensor is bad..which is what is already indicated with your wire removal test..if the relay were stuck, removal of wire would have no effect.

I can hardly believe that the sensor would fail in 4 years. What could cause this? I can change it again but is there somethng making it go bad?

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si

Poor quility control,bad connections , high relay current draw [ which I doubt ciz it is on the primary/coil side of the relay], ...
..who knows .. I just diagnose the problem

Thank you Mr. Dalton. I appreciate your responses.

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si

A similar problem exists on many 124/126 cars that have had their engine bays cleaned at the local car wash.

A sensor/relay in the fan area gets wet and the fans run continuosly afterwards. Replacement resolves the problem.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

I can't make my aux. fan come on. I have replaced the sensor but no luck. Even in very hot conditions it won't come on. Where is the end of the fan plug located? It is so well hidden I can't find it!
Mike
1984 Euro 500SL

Parents gave me their 84 190E about 4 yrs ago when they only needed their big TD.

Had A/C worked on by my Honda/Volvo mechanic. As I recall, ever since then, the Aux fan is always on. Don't recall that it was always on prior to that visit.

In the past year, the A/C 16 amp fuse blows occassionally. I normally keep the blower setting at 1. Noticed one time that when I put the system on defrost ( which induced fan high speed automatically), the fuse blew immediately. Spouse drives the car mostly, so I don't know where she puts the fan switch.

Prior to the last time the fuse blew, my wife reported that cool air stopped coming out of the vents, but blower still ran. She said she poked around on the buttons on the climate contro unit 'til it started again. I don't know if that helped or hindered. I replaced that with a rebuilt one after the first A/C service which left the fan on always. I replaced it because the push buttons would get stuck in various positions, sometimes, two in at once.

Also, when heat is called for, I hear a rapid clicking to the rt of the glove box in the dash. Like a solenoid or relay is trying to open for heat. It's the unit with all the vacuum hoses for vent controls and electrical harness to the Climate control unit. In the course of looking there, I discovered what is the aux blower. It was in a rubber case. ( I thought there might be a relay in there, even though it only had a two wire connection). The motor itself was really gummed up and hard to rotate. I cleaned it up and re-installed, hoping that it would reduce the electrical load and stop the clicking ( supposing that there was a feedback circuit which the motor was part of causing the relay sound) A red herring, I suppose.

Anyway, sometimes I hear noises coming from the blower motor which are not normal. ( Not nearly as bad as the horrid grinding sound coming from our 88 Volvo's blower. I don't drive that car, so the noise doesn't bother me!).

Where could that excessive load be coming from which pops the fuse? Is the cool shut out related to the load on the circuit?

Should I replace that blower motor from a salvage yard? ( I've located 4 190's in a local yard). I have a Haynes manual whose electrical schematics and relay configurations are do not match my car's wiring.

Anything I can check without taking it to the MB joint or some other mechanic?

M. Murrell posted in this thread that the always on fan could be a relay in or around the fan. Where would that guy be?

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Bob Tifft
84 190E (122K)
88 Volvo 240 DL (255K)
92 Honda Accord (184k)

is the fuse that blows the one for the aux cooling fan in front of the car behind the grille? it sounds like that's the fuse that keeps blowing from your post. try cleaning the contacts to the fan resistor (on my 91 190e 2.6, it's a silver box mounted behind the driver's headlight). the contacts can get corroded and dirty which can cause a higher draw which may blow the fuse.

the aux fan is (when the a/c is on) on because of the pressure swx in your a/c system. it aids in cooling the condensor. if the aux fan is on when the a/c is off and the engine is cold, it could be a bad coolant temp sensor. when they go bad they usually short to ground which keeps the fan on constantly.

the climate control box behind the glovebox is a weak point. it controls the blend doors, air direction, etc. mostly with vacuum.

hope this helps.