I have 1998 Infiniti i30. The compressor clutch will not engage properly. So far I have:
passes all self diagnostic test.
I had the system evacuated, installed new dryer canaster and triple pressure switch.
charged system to proper capacity.
check all fuses and relay.
checked continuity of all wires between the LCU, ECM, compressor, triple pressure switch, fuses and relay.
replaced LCU unit.

nothing helped.
If I jump terminal 2 on the a/c relay to a body ground the compressor engages and air blows cold.

any idea what would cause the this ground to be missing?

 

I have a friend with a 2011 Honda Civic. The AC blows hot air, turns out the AC compressor clutch relay is not sending power to the ac compressor clutch. I am able to bypass the relay and send power directly so that the AC will work, but doing that means it's always drawing current even when the car is off (guess how we found out).

 

On my 98 i30 I had an issue where the ambient air temp sensor wiring was broken and it wouldn't let the compressor engage. That's worth a look.

 

Has the AC ever worked during your ownership? If you're able to make sense of wiring diagrams (I generally can't) then I guess try and find where the ground for that relay is supposed to go. Do a continuity check, and clean up the terminal and spot on the body where it attaches. The wiring on these cars is getting old and brittle, so it's very possible that the wire broke or is hanging on by a thread. Could also be rodent damage. I take it you swapped relays around with no change?