a/c pressure switch

In a/c high pressure line from compressor to condenser usually.

 

That is the low pressure side or suction side, high pressure runs from compressor to condenser, the coil in the dash.
With ac running suction line is cold, high pressure side is hot.

 

Condenser is mounted in front of CAC. It condenses refrigerant gas compressed by compressor to a liquid.

 

The coil in the dash is the evaporator. The one in front of the radiator is the condenser

 

Mine on my freightliner is located on the air drier there’s two one is high pressure which cuts a/c compressor off at high pressures keeps from blowing seals hoses etc I think it also kicks the fan on too you hear trucks always kicking on and off while idling that’s why you hit the override switch to keep from wearing out clutchfan the other one might be fan switch can’t remember I have a book in the truck anyway if that’s the type you have I’m guessing it’s the same as my 99 and O1 freightliner it’s easy to change as the drier has an air fitting like a valve stem on a tire so you can remove the switches without losing any Freon I just replace them both and keep any good ones as spare for future diagnosis my truck has a fan switch on firewall under steering column it causes fan to come on in the winter or anytime in fact mines doing that now time to replace it again my last truck 99 had a bullion on it freightliner in Youngstown loaned me a crimp tool and had to put new plug on to fit upgraded fan switch as I recall funny a dozen or so mechanics before hand never heard of such thing I had same problem on 92 western star they simply moved the switch from middle engine area to firewall don’t know what your trucks symptoms are but the way to ID the high pressure switch on mine is unplug it and a/c comp shuts off either way look on top of a/c air drier then question dealer parts and mechanics it’s either one of those or the other thermostatic fan switch on the firewall had a problem last summer high pressure switch replaced 2 times before figured out the plug it self was bad bought new plug ie pigtail fixed problem same with radiator low coolant sensor kept acting erratic over a few years it gets wet after truck wash shutdown unplug runs about hour later shutdown plug in runs finally figured out had broken wire in plug new pigtail no more prob good luck hope you figure it out