Asked in Mercury Grand Marquis
Why did 2004 grand marquis climate control fan stop working?
First unplug the power from the fan located on the firewall on the passenger side. Use a jumper wire from the battery to the fan contacts. If it runs fine then your three speed control module ( it is a circuit board approx 4 inches by 2 inches ) is the problem. It is a known problem and the new one purchased has a different part number from the original and incorporates a fix for the problem.
This electronic module is located inside the air ducting fastened to the firewall. The board is just below the heater hose inlets going through the firewall. It is held on by two small hex head screws and is very difficult to get to, but can be done with patience and care. The heater hoses ( both inlet and outlet have to be removed along with some other parts in the way. It took me approx. 3/4 hour to change it and replace the lost coolant.
Sorry I don't have the part number but it costs $72.00 retail and $40.00 wholesale at the Ford dealer. For a dealer to diagnose and change I was quoted $380.00.