Cooling fan runs all time - 1993 Mercedes-Benz Mercedes Benz 400 Class

Both radiator cooling fans are running all the time ? Key off ? The cooling fan opperation
HOW they work
Cooling Fan Control
The engine cooling fan system consists of 2 cooling fans and 3 relays. The relays are powered by the battery positive voltage circuit and controlled by a switched ground from the powertrain control module (PCM).
During low speed operation, the PCM supplies the ground path for the low speed cooling fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan low relay coil, closes the relay contacts, and supplies battery positive voltage from the COOL FAN LO fuse through the cooling fan motor supply voltage circuit to the cooling fan. During high speed operation the PCM supplies the ground path for the cooling fan low relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan high relay and the s/p cooling fan relay through the high speed fan relay control circuit.
The PCM commands the fan on under the following conditions:
• Engine coolant temperature exceeds approximately 98°C (208°F) Low Fan Speed
• Engine coolant temperature exceeds approximately 102°C (216°F) High Fan Speed
• A/C refrigerant pressure exceeds 361 kPa (52 psi) Low Fan Speed
• A/C refrigerant pressure exceeds 2100 kPa (300 psi) High Fan Speed
• When the engine coolant temperature exceeds 112°C (234°F) at key off, the fan high speed will run for up to 300 seconds. If within that time frame 102°C (216°F) is reached then fan speed will change from high to low speed. If within that time frame 99°C (210°F) is reached then fan speed will change from low to off.
The PCM commands the fan off under the following conditions:
• A/C is requested and engine speed exceeds 6,240 RPM
• Engine coolant temperature exceeds approximately 99°C (210°F) turns the cooling fans from low to off.

sounds like one of the relays are stuck closed .

Cooling Fan Always On
Step
Action
Yes
No
Schematic Reference: Engine Cooling Schematics , HVAC Schematics in HVAC Systems - Manual
Connector End View Reference: Cooling System Connector End Views
DEFINITION: One or both engine cooling fan motors run continuously in high or low speed.
1
Did you perform the Diagnostic System Check - Vehicle?
Go to Step 2
Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2
Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, command the Fans Low Speed ON and OFF.
Are one or both cooling fans ON?
Go to Step 3
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
3
Are both cooling fans running continuously?
Go to Step 4
Go to Step 6
4
Are both cooling fans running continuously in high speed?
Go to Step 5
Go to Step 7
5
Test the low reference circuit of the A/C refrigerant pressure sensor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 18
Go to Step 14
6
Important: The S/P relay is located under the front bumper on the drivers side of the vehicle.
Remove the cool fan S/P relay.
Did the right cooling fan turn OFF?
Go to Step 10
Go to Step 8
7
Remove the cool fan LOW relay.
Did the cooling fans turn OFF?

The cooling fans should come with a sensor and tells fans to come on at certain temperature

When your idling at a stop or parked an the engine is running A/C on cooling fans should be running . When your driving down the road air flow through the condensor is good enough and the fans don't run .

check battery volt & check line ware to system.

most time coolant temperature sensor faulty.but check cooling fan fuse and relay.then hot wire the cooling fan if fan runs.problem in the fan wiring or pcm.if every thing else okay.if cooling fan dont run when hot wired the cooling fan need replacing fan motor has internal open winding circuit.

One cooling fan runs when the engine reaches a certain temp. The second cooling fan is designed to run when the a/c is turned on, providing more air flow throw radiator. However, it will cause no harm or damage if both fans run at the same time, with or without the a/c turned on.

cooling fan will not come on until about 230 degrees, if fans still do not work. check the fuses and relay. if ok then run a wire to fan from battery.on fan side connection, run a wire from battery positive to fan connection. run a wire from negative to ground connection.if fan will not come on it is either bad or the coolant temp, sensor is bad. because this sensor send info to pcm from various running conditions. it is very important that this sensor works. it can cause;

Extended crank time when the engine is cold

Poor fuel economy

Spark knock

Lack of engine power

Erratic and/or high idle

Engine cooling fan stays running all the time

Engine cooling fan fails to turn on

Engine overheating

assuming fuse and relay are good..no fan should be running when the engine is cool/cold, the only time the fan should be running when it reach over operation temperature which then the fan kick on to bring the temperature back down to it operation temperature. both fan work in sync with one another, addition cooling is needed when the ac is running. when the last time have you replace thermostat and Thermos sensor/switch. I would replace both unit if you have not done so. The thermos/switch will turn the fan on when it reach certain temperature and cut off when it sense the temperature drop in the engine.

If the fans are running long after the car is shut off, the fan relay is fused together. Unplug the cooling fan relay and get a new one. Don't drive it far without that relay though. Put it back in and drive to your supplier.

the fan relay is bad