Coincidentally, I replaced the thermostat about 6 weeks ago due to the heating element going bad, radiator fan was on full throttle all the time and had a CEL code to support the replacement. Everything seemed to be working o.k., but will not swear to it. Right after I replaced the thermostat, I did let the motor idle in the garage until I got the fan to kick on. Thought everything was o.k., but now I question if somehow that is affecting the fan from running. However, I would think that the a/c would override that and the fan should work, but seems only to work when the coolant temperature is below 180 degrees or so.