tergis

My 2006 has a problem with the AC fan. It won't run until the air temperature is high enough.
On a hot day it will start up after a minute or two, but on a cold day when I try to run the heater it can take up to 15/20 minutes before the fan will start.
Once it starts it works normally. Sometimes when the car is warm but the fan hasn't started, if I turn the engine off then start it up again, the fan will start right away.
It has gradually got worse over the last few months, and takes longer to start than before.
Everything on the dash looks fine, the lights etc all work normally however the fuel gauge is sometimes pessimistic and reads up to 1/4 tank less fuel than is really in it. This is intermittent but also getting worse, it reads low most of the time now. Sometimes it also starts working properly when I stop and restart the engine. No idea if it's related but it seems like it might be.
I tried disconnecting the battery overnight to reset the ECU but it didn't help. Any idea what might be causing this?