HI Please tell me how the fan in the front of the engine should work, we had the fan switch replaced when we start the car the fan turns faster before it was slower is this correct, is this how it is supposed to work- Merc 1985 200

engine rad fan, AC front condensor fan.???
all have fuse
all have relays
we test those
and even hot wire fans to make sure fan even works.
or cab blower fan dead.
we can not guess fans, ever, learn to be specific, even tell
exactly where it is.
some cars have 4 fans, 1 cab and 3 up front, or just 1 huge one up front, and I and not guessing your country or engine so , I STOP

the ac fan starts as soon as the ac is switched on
the fan is provide cooling of the condenser before the radiator to prevent high head pressures in the ac compressor
it is the fan at the front of the car mand does not affect engine temp
there is a radiator fan between the engine and the radiator that will not start until the coolant temperature reaches a set temp at which point the ECM switches that fan on
if that fan is not working when the engine is hot , check for fan, coolant temperature sensor switch , fan relay, fuses or problem ECM

overheats at idle only are typically the fan system. Cars use the fan to pull air across the radiator for cooling. Any speed over 10 mph there is more than enough natural wind to do this without a fan. If the problem immediately goes away when you start moving, it is probably a malfunction or issue with the fan. I have on more than 1 occaision had a customer tell me they had the fan replaced and car was still overheating, and it ended up thje fan was spinning backwards or not turning on because of a fuse or relay issue.

If it doesnt cool down fully once speed is above 20mph for more than 30 seconds, there may be other issues like plugged radiator or weak water pump impellars. water pump is a fan that moves water instead of the air. if the blades wear, they still kinda work, but at idle they work poorly because the broken blades only move a little air at low speed, rev the engine up, they spin faster and work better. If the fan is functioning OK (Turns on and off by itself) and car still runs warmer at idle than at rev, water pump may be worth investigation.

Defective fan clutch, if it has one. With a cold engine only, try spinning the fan blade by hand. If it does not turn freely, the fan clutch is defective. Warning: When the engine is hot, the fan can turn on by itself with the car not running and keys are NOT in the ignition.

The fans are radiator cooling fans. They are temperature controled so when you first start your engine in the morning they should not run - UNLESS you start it with your AC on. If you turn your AC on one of them should start operating and the other one will kick on when your engine starts getting hot.

radiator fan switch. it is a coolant temp sensor near the thermostat goose neck that tells the computer to turn the fan on! good luck! is the check engine light on?

fuse or relay is where I'd start

Hi.....

The Normal Temperature Range to the Fan Start is: A/C ON 181 F.
A/C OFF 199 F. When the Engine Reach this Temperature the Fan should start.

OK. Do this simple test.
1---- Start the engine, Desconnect the ECT Switch located on the Radiator,
See if the Fan come ON. If yes, if not go to step #2
Connect the ECT SWITCH and leave the car Running and with a Temperature gage.
See the temperature, if the Temperature go more than 199 F.
Turn the Engine OFF.
Disconnect the ECT sensor and check for Ground at the WHITE/BLACK wire.
If ground exist, Replace the ECT switch.
But if not. Check the wire for any damaged, and the ground at the Front Left Fender.
Repair as need.

2---- check the Fuse link RDI FAN . 30 amp.
Check the Fuse link CDS FAN 30 amp.
Replace if need.
And Return to step # 1.
Check the Radiator fan Relay, Rad fan relay 2 and 3. Replace if need.

Ok. I hope this help on your question.
I can give to you the WIRING DIAGRAM of the Fans, But I need a E-MAIL adress to do that.

Thank you for use fixya....

this not really a problem as the fan speed is controlled by the high preasure switch in the ac system the hotter it is outside the higher the preassure will be in the system as hot as its been the preasure is high already when the compressor cycles it pulls suction on one side and outputs high preasure on the other the fans cool the condenser the higher the ambient temp the faster they go so all is fine...

On some car, like in my renault, there is an additional fuse box near the engine.
Buy the complete Haynes manual for your car, it will show diagrams and picture of all parts, and eventually tell you which fuses and parts are involved in the radiator fan wiring.
Once you have the diagram you follow the circuit leading to fan and find the fault, it shouldn't be complicate.