After the brake booster replacement works, one of the o-rings in the temporarily removed pipe was faulty during the first recharge attempt. I had left the o-ring unreplaced as it looked okay, but i should have taken the advice seriously and replace them anyway. Single use only..
The recharge procedure is as follows;
The system is purged to a complete vacuum of 1 mBar for the duration of 20 minutes. This will boil out residual moisture, and evacuate and recycle remaining refrigerant.
After 20 minutes the vacuum pump is shut down and the system is monitored during 3 minutes. The gauge should remain near or on 1 mBar without leakage. During my first attempt the pressure jumped to 100mBar within minutes, indicating a serious leak. At that point the cabinet refuses to fill it with refrigerant.
I was able to reproduce the leak measurement back at home with a vacuum coolant purge system (basically a venturi pump) and an aircon gauge kit. These gauges connect to the service ports of the aircon, and the low pressure gauge roughly indicates vacuum. The purge kit is connected to the third (middle) port of the gauge kit, the one normally used to connect to the refrigerant container.
85% vacuum can be established with the venturi, and overnight the vacuum gauge moved significantly because of the leaking o-ring. Happy times, #not, as the front clam had to come of again. After having replaced the suspected o-ring, lubricated with some A/C oil, the system kept its vacuum for days. Not showing any movement on the gauge.
This was confirmed during the repeated re-gas purge cycle. The system proved airtight, staying at 1mBar for minutes. Recharged with 550 gram R407a, 5 grams PAG oil and 5 grams UV oil. There was no oil extracted during the initial evacuation. (Note: s2 Toyota denso R134a based system)
Note that an A/C circuit may prove airtight under vacuum but leak under pressure, or vice versa, as o-rings and connectors may shift under load. A positive pressure test can be done with nitrogen. Needless to say pressure test, evacuation and recharge should be done professionally if the environment matters to you – aircons are bad enough already 🙂