ac high pressure sensor

[ktbtrucking]

have a truck 2004 and it has a 3 wire ac switch on firewall and i believe it measures both high and low
2002 truck has two switches one for low and one for high
high is next to radiator and low under the air filter
this is what i have figured out so far

on my 2004 truck when I turn ac on/off inside the cab insite also changes on/off the name "air conditioner pressure switch"
on my 2002 truck insite all time shows "air conditioner pressure switch" ON so that keeps fan on high speed,
also supplied "air" to radiator than it slows down

looks like ecm related issue for me

i assume tri wire switch on the firewall refers to ac switch or there is another one???