This is a great site and I hope someone might be able to help.
Facts: 1995 volvo 850 non turbo overheated in Denver and stopped on road. Intial research showed radiator fan bearings frozen and not working thus blowing a wire designed to blow out in this situation (called a fuseable link) so other components won't be fried. Radiator fan has been replaced and proves to work and the wire has been replaced. I cannot duplicate a hot situation because it is so cold here the engine will not heat up high enough to force the temperature sensor to send a signal to the relay (which works) to the rad fan. I believe the air conditioner won't automatically activate the fan as it will in the summer because the ambient temperature swith in this system is saying , hey , it is cold enough outside you don't need the air on. My next step is to replace the thermostat which a couple of Checker guys thought might make a difference. eh?? I don't know.

 

I would replace the thermostat.
I will bet it is broken.