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.

[jiggity76]

9 hours ago, 55trucker said:

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.

When I first started charging the A/C system, the driver side fan kicked on.  It might have kicked on when I actually pressed the climate control panel.  As I started filling the system...I think with the start of the 2nd bottle of freon, the compressor kicked on as well as the passenger side fan.  Yes, when I'm on the HWY or Interstate, I'm assuming both fans have shut down long ago by that point.  I can then hear them, (and feel a little bit), when I'm back in city driving mode.