I have Nissan 2006 Xterra. There is no output from the IPDM to the compressor. I have already changed the IPDM and the thermal amp behind the glove box but neither worked. Is there an easy way to check the refrigerant pressure switch? Where should I look next?

. Check all underhood and underdash fuses with a test light or multimeter.

. Check compressor clutch relay.

. Check A/C Switch.

. Check A/C Thermostat.

I don't know what the IPDM is.

There isn't a quick test for that switch (which has been known to have a high failure rate) and just as unfortunate, the system needs to be discharged to replace the switch, thus adding to the repair costs. Sorry...

The IPDM (Instrument Panel Diagnostic Module) is capable of running a self test but you shouldn't have to do that unless directed be prior diagnostics.