Hi all !
So.. I just bought a 280K km (174K miles) 2001 Subaru Outback H6 with Auto A/C. So far I can tell, it is in superb condition but as I do not have any kind of service history I tend to be suspicious about everything.
Naturally, I found this community and as the car is aging I hope there are still some people to help me out with my problem. I’m learning a lot thanks to this community.
My main problem this summer (…) is that when I want to switch the A/C on (lowest temp : 18°C) the magnet clutch is not ordered to engage the compressor.
As I do not know how old the problem is, the first thing I did was to get my refrigerant refilled (by a pro). I was told that “there was not missing much” (so no leak). And “60€ please”.
If I remove the relay switch and close the circuit myself, everything works fine. The clutch engages, the compressor does it’s job and I get cold air in the cabin. Everything seems to be working fine.
So what could prevent the ECM or the A/C control module to engage the clutch when I want A/C ?
I checked the Pressure Switch (Triple Switch) : it is closed on 1 – 2, not on 3 – 4. So from what I understood pressure is not too high nor too low.
Of course I checked the relay and it’s OK. The fuses 2, 4 and 17 are also ok (the others also).
If I connect the green test connector under the wheel compartment, it activates all the relays in sequence (fans’s, blowers…) but not the magnet clutch relay.
I ran the SELF-DIAGNOSIS MODE for the A/C control module and got trouble code 24 : The evaporation sensor.
I removed the glove-box and indeed the thermistor had been replaced by an adjustable (potentiometer) thermistor… And it was no longer working. I found the original OEM part on ebay (65€ for a thermistor 
) and thought the problem would be solved. SELF-DIAGNOSIS MODE for the A/C control module showed “20” and “30” = “no trouble”. Yeah !
But the relay is still not activated by the A/C control module.
As I can engage manually the clutch and have cold air : it is not a refrigerant or mechanical problem. The pressure switch seems to be ok. No other sensor is failing according to the SELF-DIAGNOSIS MODE of the A/C control module. So where should I look now ?
One thing I noticed is that, while IDLING, if I turn on the A/C (again, coldest setting to force the compressor to kick in), after a few second, the front motor blower (both) are turned on (as they should when using the A/C while parked)… So I do not think the ECM and the A/C control module both want (think) that the compressor is running and it’s not a faulty something (like a pressure switch) telling them “oh no ! do not engage the compressor !” (Or something similar. In japanese.)
The last item to check according to the service manual is the “wiring harness”… but I do not know where to start. If you have an advice, because I’m kind of lost right now.
