Cooling fan questions

[Megavolt-380]

TGP 1989
When operating without the air conditioner on, everything is fine. But when we turn on the air conditioner, even on a cold engine, both the main and additional fans turn on immediately. The question is - is this a normal operating mode? After all, the pressure sensor should be responsible for turning on the fans, but the control unit ignores any state of the sensor. 

[55trucker]

Indeed it is........

both the primary & secondary fans will engage.

The low pressure sensor engages the entire system when the system is above approx 40lbs, the compressor does NOT cycle, once engaged it runs 100% of the time the a/c is turned on (depending on the volume of system charge).

[jiggity76]

I just rebuilt the A/C system in the International and yes, both fans run when the A/C is on.  The fans and the compressor is doing exactly how 55trucker is describing.

[55trucker]

I should also add that the coolant fans engagement is speed dependent, when the a/c is on the pcm will disengage the fans as the vehicle speed increases to the point when they no longer need to be.