While waiting at a different garage for another car to be repaired, my air con compressor started making a really weird humming noise, like a woodwind instrument or a horn. I could tell it was the compressor because it went away as the clutch clicked out, and came back when the clutch clicked in. The new garage kindly stuck the car on their air con machine and recovered 1150g of gas and 32g of oil. They then charged it back up with 900g of gas and 5g of oil and did a quick diagnostic. With a gauge connected to the high pressure side, I started the engine, left it on tickover and put the settings in the cabin on max cold and we watched the pressure of the high side.. The compressor kicked in and the pressure rose all the way to nearly 400 psi without the compressor shutting off. We noted that at no time during this did the cooling fan near the rad start to turn. At the time I didn't know how much pressure the system would take without causing a leak/explosion so I shut the engine off. I drove the car home, running the AC only when the car was moving, and at home the compressor seemed to click on and off normally, maybe once every 25 seconds it would run for 5 - 7 seconds. The system produces cool air from the cabin blowers and it demists the screen rapidly so it's doing a reasonable job of drying the air
Cooling seems less effective when the car is standing still, and I still haven't seen the car turn the radiator fan on at any point.
At the moment I'm thinking I should test two things:
1 that the rad fan does work - hopefully I can disconnect the module that controls its speed via the purple wire, and just connect it to the battery to prove that it turns
2 that the ac pressure sensor gives a good reading - i'm given to understand that this sensor is a 3 wire one and it should provide a signal to the ecu at 200 psi (for the rad fan to start) and 400 psi (for the compressor to deactivate)
Questions:
Should I/can I get some sort of diagnostic software and cable so I can poke the computer and tell it to turn the fan on and off itself, or tell me what the AC pressure reading is etc?
I've no idea how much oil the first place sucked out of the system when they recharged it, and volvo weren't much help because they said there isn't a set amount one should add - simply that one should add back all the oil that is removed during a vacuum.. Now that I don't know if the first garage added too much, enough or not enough oil, and the second garage added 5g of oil when they removed 32g (they thought the 32g was high compared to what they normally do) but I don't want 5g to be too low and ruin the compressor
Can anyone tell me if it's even possible to determine how much oil I should add back now? I'm going back to the second garage to get them to vac the system again and add 1000g of gas.. the oil is the query though..
And if my diagnotics show that anything else like the ac pressure sensor needs changing, i guess I should get the second garage to to that while they have the system empty of gas
so if anyone can suggest another diagnostic I should run I'd be most grateful!