99 volvo engine cooling fan not working HELP !!!!

1. Check the fuses in central panel. Radiator fan solenoid is on the same fuse with inlet air heaters, not sure about the fuse number but in 10 minutes with a test light and the ignition switch on all fuses can be checked.
2. APAD module for the A/C is the little square box on the firewall in engine compartment driver side with red and green LEDs. Try and find a known good one from another truck and swap, otherwise you'll have to purchase one and it is not returnable.
3. Check your diagnostic display for fault codes. A defective coolant temperature sensor (on left rear side of the head) or a defective inlet air temperature sensor (on intake manifold, same sensor gives the turboboost pressure) could trigger a fault code because as the engine ECU knows nothing about the coolant or inlet air temperature it keeps the fan on all the time to protect the engine.
Good luck!

 

I know this is an old thread, but I'm having similar problem with my 99 VNL w/M11 Cummins. I replaced all air solenoid and fan clutch and a temp sensor, when I have the key on (engine not running) the fan clutch releases. Once the truck is running it just stays on and there is no voltage at the connector to the solenoid. What controls the voltage to the air solenoid to make it operate? Thanks in advance for a reply!