Can anyone diagnose problem from the following info:

1. Aux fan does not spin when A/C is on.
2. With car running, measured 9.01 volts at closest plug (has two wires) to the fan. Had to jump the high pressure switch to get 9.01 volts. (This seems to indicate that the high pressure switch is bad?). With measured 9.01 volts - the fan does not spin.
3. Checked ground wire a same plug and have good ground.
4. With battery voltage jumped to fan side of plug, the faqn spins fast.
Question: Should the fan spin when 9.01 volts avail?
5. Measured ~10M ohms across pre-resistor. Is this appropriate?
6. Can anyone verify that either the fan or the preresistor is good or bad?

Thanks in advance
Rick

10million ohms is too much.

The fan should run on low with the red switch bridged. It only closes above 250psi. If the compressor is on and the high side pressure is below 250, the fan may not run.

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Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM