How to Wire a Trinary Switch
From Wheels of Time
A Trinary Switch has 3 functions: 1) low pressure cut off 2) high pressure cut off (about 500 psi) & 3) preset pressure to bring on an electric engine fan (about 250 psi)
Manufactures use different color codes for wiring, this explanation should cover all of the wiring colors.
1) Connect the A/C thermostat (a blue wire if it's Vintage Air) to the black/green, black/white or black wire.
2) Connect the compressor to the black/green, black/white or black wire.
3) Connect a good ground to the blue/red or blue wire.
4) Connect the remaining blue/red or blue wire to the ground side of the fan relay (#86) or the temp sending switch that is sending the ground signal to bring on the electric fan.
