97 E420 (W210) Aux Fan problem

[apb]

My aux fan is not working. I tested the connector with the engin really hot (approaching 115-120) and my test light blinks every 5 to 6 seconds without the motor engaging. Any clues? Is it a relay issue? strange the it would be at a regular interval.
Thanks for you help and thoughts. I have not tested the motor yet, but it appears to be a power supply issue...

[e300D97]

With engine running hold both AUTO buttons down on the Climate Control system for over 10 seconds. This should put the AUX fans in HIGH SPEED mode. If not it could be the fans are just worn out. Also, the one on the passenger side is belt driven from the main one on drivers side. If the belt broke, it could be impeding the fan from turning. If you get a replacement online, becareful, the tend to be wired incorrectly. Its no big deal, you just take apart the connector and switch the wires. I had this problem last year, couldnt figure out why the fans were turning backwards.

[gmercoleza]

Originally Posted by e300D97

With engine running hold both AUTO buttons down on the Climate Control system for over 10 seconds. This should put the AUX fans in HIGH SPEED mode. If not it could be the fans are just worn out. Also, the one on the passenger side is belt driven from the main one on drivers side. If the belt broke, it could be impeding the fan from turning. If you get a replacement online, becareful, the tend to be wired incorrectly. Its no big deal, you just take apart the connector and switch the wires. I had this problem last year, couldnt figure out why the fans were turning backwards.

Ditto on the reverse polarity of aftermarket fan units. I dealt with that on mine and couldn't figure out why the A/C kept venting refrigerant out the check valve. Hooked up the gauges and saw 400+ PSI!!! Reversing the polarity via the connector as stated resolved the issue, but now my A/C compressor is a little noisy. It's too bad, because the compressor was probably a year old (new, not reman) when this happened.

[Matt L]

Do you have an aftermarket fan assembly? I had one of these fail on me after nine months of use, and it failed with your exact symptoms. It was also wired in reverse, but that had been fixed.

The fan controller is much more than a simple relay and resistor. It pulses the motor (the pulses that you saw) to start it, and reads the electrical signature of the motor during these pulses. If the signature is wrong (say, your cheap aftermarket fan motor magnets have weakened), the fan fails to start, and another attempt is made in a few seconds. If the motor bumps during this attempt, give it some help (spin the hub with your hand) to see if it will start. If the motor is going bad but not all the way gone and the controller is good, this may start it up.

Note that testing whether the fan runs with 12V applied is not a valid test of the controller. Mine ran just fine (but not as strong as new) with 12V applied, but the new OEM assembly did cure my problem.

[apb]

I have the original fan motor, about 12 years, looks like it is shot... if will not start with the initial current... I will try to find a replacement motor...