Auto Air Conditioning & Heater Repair: 01 silverado 3500 no fire at low pressure switch, chevy silverado, pressure switches

Question
Hi I have 01 chevy silverado 3500 ,my compressor wont engage unless done manually I have replaced the  compressor with clutch ,accumulator added new freon  I have no fire at low pressure switch so wont engaged the compressor, even replaced the heat and air control unit in dash when you start truck turn ac on you hear nothing.. thanks for any help

Answer
Hi Jim,

 Your system is a bit different than older ones that power up the compressor through the low pressure cycling switch.
 This system uses the CCH (climate control head) to receive various low inputs from sensors and providing all the criteria are met it engages the compressor relay which in turn allows voltage to be supplied to the clutch.  The CCH looks for ground signals from high pressure and low pressure switches, thats why you don't see power there.
 Have you checked the high pressure switch?  I have seen them go bad and not allow the compressor to come on because the CCH thinks the system pressure is through the roof even when the system is static.

Wayne