Clutch fan will not go off

[TomVertiz]

I am working on a 06 Mack with a cummins. The clutch fan will not go off. I have checked the ac pressure switch and I believe it is ok. The problem is I am only getting between 10 and 11.5 volts out of the Ecu, and the silonoide takes 12 volts to activate. The wire goes straight to the computer and not through a relay, there is also no corrosion or bad spots in the wire. I checked right out of the Ecu and there is not 12 volts. Any help would be appreciated.

[Mackpro]

What is the truck model? Is it a air fan clutch or a electric viscus clutch? If air, first shoot air directly to fan clutch (or take air away ) to make sure it will unlock just to make sure its not a bad fan clutch. It should have around 12 volts going to solinoid from fuse panel and the other wire goes to the engine ECM and makes or breaks the ground inside to engage/disengage the fan. High A/C head pressure , high intake manifold temp and high coolant temp will make the fan turn on .

[TomVertiz]

So I rechecked the the ax pressure switch. That was the problem. I let another mechanic in out shop talk me into second guessing myself. Thanks for the advice!!

[garcia26233]

How did recheck or found out the AC switch was bad? I've had same problem on a e7, coolant is ok, replaced intake sensors, only need to check AC but how?