have specific questions regarding ac diagnosis

1991 civic STD with d16y7 mpfi run off a pm6. Mitsuba compressor.

Ac started blowing warm recently. Compressor clutch is not engaging.

Jumped compressor. Hooked up gauges: everything was where I left it last year. Around 45 low, 250 high (100 degrees right now). Ac is cold when jumped (as good as it gets with 134 anyway)

Checked fuses, relays, all good.

Condenser fan is on.

****Checked circuits, not getting the ground to the clutch relay via the yellow wire that comes from the ECU.

Jumped the ground at the B3 pin, heard compressor clutch click on.

SO-

Is my ecu bad OR

Is the low pressure switch bad which is telling my ecu not to ground the clutch?

How do I test the low pressure switch?

I’d rather not throw parts at it, pm6 ecus don’t grow on trees.

 

to test your low pressure switch you just disconnect the two wire clip at the switch
turn on the ac by pressing the ac button inside the car and the fan speed to any speed
and see if you have a ground on one of the two wires on the wire connector

what ill do is connect a wire to ground and when i touch one wire on the disconnected switch connector the ac will kick on
then ill know that the OTHER wire is the one that is the ground were looking for
and that we test with a test light
if theres no ground with the ac on then the button inside the car is where you go next

good luck

 

Thanks 🙏

I’ll check it out tomorrow.

 

Yeah, the low pressure switch is fine. Incidentally, the low pressure switch also activated the condenser fan and raises the idle. Both the condenser fan and high idle are working when I press the ac switch to ‘on’, the clutch itself is the only thing not working.

I’ve narrowed it down to the ecu.

this may be the excuse I was looking for to just do a mini me, as I already have an extra p28.