After one of the first fires of the car back when I was getting it up and running again, I tried the air con as part of the ritual of pressing all the buttons to see what worked and what didn’t. The air con tried to kick in and then tripped out. Having ensured the relay and fuse were ok, I had to dig deeper. I had read that there’s a pressure switch that detects low pressure so I assumed this had detected low pressure due to leakage over time and tripped out the compressor.
To confirm, I dug out an old gauge/refill set I had in the garage. The idea is the gauge connects to the low pressure connection and reads the pressure, but it also has a tee-in connection for a refill bottle to rectify low pressure. Step 1 was to confirm low pressure, so goggles and gloves on, I set about connecting up the gauge. In advance of this, the instructions call for ensuring there is a demand on the air con system so the engine needs to be started, air con set to max cool (with the air con on obviously), run for a few minutes to get to steady state. Tellingly, the compressor wasn’t even trying to start. Prerequisites met, it was time to hook up the gauge. I’ve only a picture of the gauge with refill bottle attached, but the picture shows the blue connection into the low pressure tapping point (the light blue dust cap marked ‘L’ is removed and on the bottom right of the pic)
The gauge read zero, so the system is fully discharged, it had obviously leaked over time. I had read that the o-rings on Subarus tend to leak at the high and low pressure connections into the compressor so it made sense to replace these. Air con o-rings are made of a particular material designed for the purpose so I procured a couple.
The two connections were disconnected with a 12mm socket, using penetrating fluid as a precaution. Obviously I only felt comfortable with this step in the knowledge that the system was de-pressurised. In both cases, the connection comes away quite easily, exposing the o-ring (new o-ring shown fitted here in green). The old o-ring was removed with a pick, being careful not to score the metal.
While I had these off, I cleaned the nut threads and the mating faces to give them the best chance of working.
Bolts torqued up, it’s time for the recharge. The kit has a trigger to allow you to release R134a into the system. So, before filling, like before, the engine is run, air con to max cool. Pulling the trigger for a few seconds sees the pressure build up, so I slowly built it up to around 10psi. Now the pressure switch was seeing pressure so the compressor cut in. This drops the pressure on the gauge, as the circuit is now fully in play and the small amount of refrigerant loses pressure across the whole circuit. The compressor is cycling in and out at this stage, trying to do its work. Now that it’s holding pressure on the LP side, I tried charging it up while the compressor was running. This is done very carefully and deliberately, rotating the bottle and watching the gauge carefully. After a while, the bottle was emptied (500g, roughly the capacity of the system – I should also note that the refill kit also contains refrigerant oil which is crucial to correct operation of the system) and the gauge read >25psi even with the compressor running. At the end, the compressor is cycling on and off, pressure is holding, increasing on the LP side when the compressor cuts out and nice chilly air is blowing from the vents.
Result! And just in time for it to lash rain.