I have an 03 GT and the engine stays cold when the defroster is running. I also think the radiator fan is staying on all the time but haven't checked today. I turned the defroster and heater off today and the engine temp rose normally, I turned on the heater and the temp remained normal but, when I turn on the defroster the engine temp drops all the way down to cold. Could this be the CCM failing and causing the fan to run all the time? I've had to replace one fan and fan relay already. I've changed out the coolant temp sensor and replaced the thermostat. I am at a loss as to what it could be other than the CCM or potentially the ignition switch. Any advice would be appreciated.

 

the fan will run whenever the ac compressor is cycled on. and defrost mode will cycle the ac compressor

 

I believe the fan is running even when the defroster/ac is off.

 

I found the problem. It didn't seem like a logical cause to my cold running issues but, what I did seems to have worked.
I could drive this car for 15 or 20 miles in the winter and the engine would stay cold the entire time, barely coming off the C mark on the temp gauge. It would warm up while sitting in the drive and the engine running, but as soon as I would get out driving the temp would fall again.
It was summer and the AC wasn't working like it should, the air just wasn't that cold. I had the freon recharged and that fixed the AC issues. This winter I was expecting the same issues I had with the engine to return but, to my surprise, the engine began to heat up properly and I haven't had any more troubles with it.
I had spoken with several mechanics and none of them could figure out what the problem was. No one even asked about the AC freon charge.

 

I had the AC charged with freon and that fixed my problem. It seemed counterintuitive but, it worked.

 

I can assure you the ac charge level does not affect the performance of the cooling system, but if all is well now then rock on