1999 Dodge Ram Pickup a/c random

this truck has 193k miles, the a/c works fine most of the time, but the clutch will not energize and spin the compressor randomly.

I have jumped out the pressure switch, no avail, swapped clutch relays, no avail…looking for ideas,…one guy said its the “flap door”

how can I figure out which signal is misssing?, since I am too cheap to buy a shop manual, and the last time I took it to the dealer, he tried to sell me a new computer when I had told him the alternator was bad.!!!

A outside ambient, or evaporator temperature sensor reading wrong, I guess could cause this. But without having it hooking it up to proper diagnostic equipment your only throwing parts at it, and in the long run could cost more by being a parts changer.