There should be a live on one of the black/yellow wires at the triple pressure switch.
The only component between the a/con switch and the triple pressure switch is the evaporator temp. switch. Power comes into the evap. temp. switch on a black/white wire and, assuming there is no problem with it's operation, comes out on the black/yellow wire and then feeds the triple pressure switch.
I have replaced evap. switches before, not the easiest job.
Experience is something you don't get until just after you need it!