I HAVE MB C220 1994, THE AUXALLARY FANS NOT WORK I ALREADY CHECKED BOTH FUSE RELAYS , BOTH OF THEM OK, BUT NO VOLTAGE COMES TO ACTIVE THAT RELAYS (ALL FUSES ARE OK ), WHEN I REMOVE THE PLUG OF TEMP. SWITCH SENSOR OF WATER ALSO BOTH FANS NOT WORK, BUT WHEN I PUT A JUMPER BETWEEN 30 AND 87 POINTS IN HIGH SPEED RELAY BASE THE FANS WORK. SO PLEASE ADVICE OR SHOW ME WHERE I CAN GET THE WIRING DIAGRAM FOR THAT SYSTEM
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If the heater fan is not running; 1. Check the fuse first of all.
2. Check if the fan is running when connecting 12VDc directly to the fan. If not running . Replace Fan.
3. If Fan OK - check the voltage on the connector from the fan between red and Black wire. Must be 12V
If no 12V - Supply voltage is missing - probably fuse defect.
4.If 12V = OK - measure the voltage on the Violet wire in the connector. When button on dashboard is set to "Fan active" You must measure a voltage here close to 10VDc. If OK Fan Resistor/Regulator defective.
5 If no voltage (10V) on the wire (violet) when set to "Fan active" controlboard behind the dashboard defective.
Fuses ok? The fan (I presume we are talking about the radiator cooling fan) is controlled by a thermostatic switch. You need to check that this switch is closing it's contacts when it gets hot (and this most likely is the cause of your problems) If the switch is functioning correctly there will be a relay which it controls. The next thing is to check that this relay is switching when the thermostatic switch closes. If the fuses are ok, the thermostatic switch is ok, the relay is ok, then check at the fan plug that you have voltage when the fan should be running. If you have voltage and the fan does not run, the fan motor is U/S and will have to be changed. If you have no voltage then you have a wiring problem. As I say, the most common failure item is the switch, followed by the relay.
There is still a relay you can check in the same fuse/relay box you checked the fuse in. swap it with the windshield wiper relay or one that is of the same design size and color. This will rule out power issues. You can also unplug the fan and run a power and ground wire from the battery to the fan connector to momentarily hot wire the fan. If it sounds nice and quiet with out growling, only the steady hum/drone of the fan then its ok. Just remember that the A/C fan only comes on when the A/C is on and the primary engine fan only comes on when the vehicle is getting to its thermostatic activation point. I hope this info helps.
The computer on the vehicle is responsible for turning on the relay and activating the fan.However I would probably apply battery voltage through a length of wire directly to the fan to see if it comes on first. If not than there is a problem with the fan motor. If it comes on, my next step would be to start the vehicle and put A/C on high. (Fan should always be on when A/C is on) If it is on then the computer and wiring are fine. I would then be checking coolant temp sensor and verify the cooling system is full.
Check the fuses and relays, the cooling fan relay is bad about going out on these. It can be found in the right fender well under the headlamp. If the fuses and relay is ok then check for voltage at the fan itself, if you have voltage at fan then replace fan assymbly. You will have to pull right headlamp to access fan relay.