Fan running when temperature is normal.

A/C running will signal turn fan on when pressure gets high. Not a problem.

 

where wire harness comes out of rear harness of ecm,look for worn insulation on wires.pin v-4 is fan output wire.i will bet more than one wire is exposed,terrible design flaw with harness looping down.good luck.

 

Is it only happening while a/c s on? batmick is right. I got an 06 and it turns on radomely but only if a/c is on in front or sleeper. Normaly it should come on a little over 200 unless you hit the over ride switch. If it is truely coming on not do to a/c....it could be anything from a leaky fan cluch to bad electronics to bad ecm. Could even be a bad override switch.

 

The fan will come on at whatever temperature it is programmed to come at. No specific temp.
If it is coming on when the AC is off, check the solenoid and airlines first. Cheap part to replace, and very doable yourself. The solenoid could be hanging up.
Also, does your fan spin freely when the engine is shut off, or does it lock up? Some need air to release, some need air to lock.

Martin

 

Also keep in mind that the A/C will cycle with the defrosters on, even if the A/C is off.

 

on an 05 columbia, the a/c light shows it on when you switch to defrost. Setting bunk to low will also turn it on.