AC clutch not engaging - tested the following

[Roler]

Summary to keep it short, following a few hours of diagnostics.
AC clutch not engaging, did the following diagnostics on the relay and the low pressure switch (LPS)

With the low pressure switch connected:
Key ON or engine running. measuring at the AC clutch relay sockets: 86 has power, 85 has ground, jumping 30 &87: clutch engages (but no cold air)

With the lower pressure switch jumpered at the connector:
Key on (not running): power at socket 86 and ground at 85
Key in run/engine running: power at 86, ground at 85, aux fan comes on, clutched engaged the 1st time, but not on the 2nd test or the 3rd test

With the relay out and the LPS jumpered:
Key ON/or engine running: NO continuity in the LPS

With relay out and LPS jumpered:
key in RUN (ON): 86 has power, 85 has ground, jumped 30&87: clutch engages (no cold air)

Shortly pressing the low pressure service port shrader valve releases pressure, suggesting I have at least some refrigerant (I know this is not THE test, butI don't have AC test equipment/gauges )

Tested the AC clutch relay with power probe and multimeter - it is doing all the right things


So my confusion here ( AC is not blowing cold air) re the following:
- no continuity at the LPS would suggest the LPS is faulty; however the PCM grounds at 85 with key ON , suggesting the PCM sees all the requirements and is happy to provide ground at 85 to 'activate' the coil on the AC clutch relay

- I measure NO continuity at the LPS (both without and with key ON as well as engine running) which suggest the LPS is faulty (or low in refrigerant, however pressure escapes the shrader valve when testing)-
how come the PCM still grounds 85 socket, which suggests the PCM is happy with the info it is getting from the LPS??

-With the relay out, I have power at 86 and ground at 85 and jumpering 30 and 87 engages the clutch- suggesting the AC relay is faulty while it tests perfectly fine with every single test on the relay (tested out of the vehicle)
It would suggest once in place, the relay is not functioning which would indicate a fault at the socket, like loose sockets... - but I have nothing suggesting this


I am a bit stumped by what I measure and find- happy for any input!

[amlav]

From my experience I would say low ac gas in the system .
Start the engine , turn the ac dashboard switch ON than go back to engine bay and remove the Low Pressure switch wiring from the top of the switch connector socket . Bridge the 2 wires of the wiring loom toogheter . If clutch engages than you have low gas presure . Don't run it like this for too long because the gas has lubricating oil mixed with the gas and if low on gas not much lubrication of compressor pistons is happening .
Hope this helps .

[Roler]

This was already done, as described.

Besides: the LPS shows no continuity, jumpering the connector did not change anything BUT the PCM still provided ground, which means the PCM is happy with all the input it gets and provides ground to the coil of the relay to activate it. Which it should NOT be doing if either the gas is too low or the low pressure switch is faulty (in the later case, jumping the connector would make the system work).

I was thinking the only thing I have not been able to check is the refrigerant pressure (because I don't have the equipment)
However, even if the pressure was too low, the PCM should not be grounding the clutch relay

[amlav]

Not sure about your car but my xj diesel also had a High pressure switch near the compressor as far I remember.
There could be a logic in working first time for a minute than not .
Maybe there is still a bit of gas in the system and it pressurise it at the begining but as gas gets depleted will activate the low pressure switch and disable the compressor clutch.
Just a thought ......

[Roler]

Yeah I haven't checked that high pressure switch because I thought it's not involved in the clutch not engaging initially.

Maybe I'll buy an el cheapo gauge set on ebay (since I'll never use it again most likely) so I can check the pressure myself

[werd]

My AC stopped working, tracked it back to the coil that engaged the clutch had burned out.