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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54034
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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99 Mercedes c280 the radiator fan is not turning on with a/c

Customer Question

99 Mercedes c280 the radiator fan is not turning on with a/c on. it has codes 421 & 422 compressor is working but not cooling high side pressure is going up to 450
Submitted: 2 years ago.
Category: Mercedes
Expert:  Marty replied 2 years ago.

Hi, the first thing you need to do is test for power to the fan. If you have no power to the fan you probably have a bad fan control module. Fuse 38 powers the module. Check the fuse first. If the fuse is good and there is no power to the fan your module will most likely need to be replaced.

Let me know if you have any questions.

Marty

Customer: replied 2 years ago.
i have change the fan control module & check fuse 38 I also have install a used control. also check fuse 20-29-30. all fuses are good. there is power at red & yellow at module & ground at the brown wire. also the wires to the fan to relay are good
Expert:  Marty replied 2 years ago.

Can you post the last 8 digits of the vin number?

Customer: replied 2 years ago.
xa787343 do you know what codes 421 422 are
Expert:  Marty replied 2 years ago.

How did you come up with those codes?

Customer: replied 2 years ago.
off the heater control by pressing the buttons you can get all the sensor outputs
Expert:  Marty replied 2 years ago.

421 and 422 are fault codes for the auxiliary fan and the serial communication from the climate control module. Do you have power to the red/white wire at the fan module? If you do, I would question whether your used module is any good.

Customer: replied 2 years ago.
its a new fan control module. but i do not have power at the red & white wire
Expert:  Marty replied 2 years ago.

The red/white wire comes out of the left front SAM. You need to go to trace the wire back to the SAM and see if you have voltage.

Customer: replied 2 years ago.
already did checked no power coming out & also tried another sam module
Expert:  Marty replied 2 years ago.

Is fuse 41 installed? Is there power to fuse 41?

Customer: replied 2 years ago.
fuse 41 has power & the fuse is good
Expert:  Marty replied 2 years ago.

Are you sure you are checking the correct wire at the SAM? If you use your power probe to put power to the red/white wire at the SAM do you get power at the module?

Customer: replied 2 years ago.
checked red & white wire & battery must have went down from checking. charged battery & checked & i have 12.83 volts. also I found if I disconect green wire fan came on. it was on high speed but still will not turn on with a/c. but works ok when engine heats up
Expert:  Marty replied 2 years ago.

Is it the original a/c control head? Have you checked the coding of the head?

Expert:  Marty replied 2 years ago.

Key off - press and hold REST button - turn the key on - release the REST button - read the coding on the display.

Customer: replied 2 years ago.
It came up 00p but when I held the rest & defrost button it had code 421 422
Expert:  Marty replied 2 years ago.

00 is probably correct. Try changing the coding to 02 and see if it works. Then try 10, 18 and 32. It sounds like the a/c control head may be bad. Have you already replaced it?

Customer: replied 2 years ago.
I did replace the control head And it came up with the same codes
Expert:  Marty replied 2 years ago.

It looks like the data flows from the N22 to the instrument cluster. I'd check the wiring from the N22 to the cluster. The blue/yellow wire from the N22 goes to the cluster.

Customer: replied 2 years ago.
my diagram shows ac control to pin 17 at cluster blue & yellow is that the wire
Expert:  Marty replied 2 years ago.

Yes that is the wire.

Customer: replied 2 years ago.
Marty checked the blue & yellow wire its ok from control to cluster all is ok Mercedes did put a cluster in about 1yr ago because you could not read miles but i think everything was working ok
Expert:  Marty replied 2 years ago.

Are you able to check the coding of the instrument cluster?