I noticed my AC not getting cold, so I took a look at the components. The AC compressor clutch is no longer engaging, the issue seems electrical. I do get a good ground from the AC clutch relay when switching the AC on, so the relay should be switching the clutch to engage.


To make sure the system is not low on refrigerant I have measured the voltage at the pressure switch, which has a good ground so the system must have sufficient pressure.
I do not want to risk damaging the compressor, so the tests have been done with the compressor clutch wire disconnected from the clutch and attached to a multimeter to measure the output.

After multiple measurements I narrowed it down to the relay power supply (white/blue wire WU top left of diagram), which has only 0,2V instead of the full 12V! Fuse is not blown. Does anyone have a clue where to go next? Could it be an broken cable or corroded connector from fusebox to relay? Is it a smart idea to cut the existing wire and solder in a new one from the fuse directly to the AC relay connector, bypassing the existing cable?


Summary:
- Clutch will engage when forced 12V
- Relay is being operated by the ECU, I measure ground on cable RY when AC is on, 12V when AC is off.
- Pressure switch has good ground, thus pressure
- Relay has been switched with another one, no changes
- Car has had the always-on fan modification from the dealer so some cables have been cut near the fuse box

 

Have you checked the refrigerant pressures? If there is a leak and the pressure falls too low, the compressor won't engage as a protection mechanism. Are you sure you checked the right pressure switch for continuity?

 

I checked the pressure swith located near the bulkhead. Got a ground connection there so pressure must be good. Or am I mistaken and is the sensor designed to make a ground if pressure falls too low?
I'll jump the sensor and measure the output of the relay without the compressor attached (to avoid damage), so if i get a 12V signal then the pressure must be too low..

Also, the switched ground at the relay is functioning, so the pressure switch must tell the ECU there is sufficient pressure?
Only problem is there is no 12V power supply going to the relay, but perhaps this power supply is also switched?

 

I noticed some cut wiring at the fuse box. Someone added a new wire which goes somewhere near the alternator.

Perhaps they cut the wrong wire (or before the splice) at the fuse box which means I do not get power to the AC clutch relay. Still doens't explain why I get 0,2V at the relay instead of 0V or 12V..

 

Couldn't see if this is in the above, but... oops I see fuse is not blown...

 

FIXED!

Some mechanic 'fixed' the alternator warning bulb, which shares the same fuse, by cutting the wire from the fuse and placing a new wire from the alternator to the fuse bypassing the OEM connector. The OEM connector splices the wire going to the alternator AND the AC clutch relay.
Soldered the wire back in place and the AC works!