Evacuate and Recharge
EVACUATEWhenever the system has been opened to the atmosphere, it is necessary that the system be evacuated to remove all air and moisture. It is also an essential preliminary operation to charging the system with Refrigerant 12. The evacuate operation also provides a check for leaks due to faulty connections.
1. Discharge the system as previously described and connect the charging and testing equipment referring to the manufacturer's instructions.
2. Slowly open the vacuum control valve. If the vacuum is applied to the system too quickly, the residual oil may be drawn out.
3. In evacuating the system it is necessary to lower the pressure so that the boiling point of water in the system is lower than the surrounding air temperature. At an ambient temperature of 23.8°C (75°F), it is necessary to lower the system pressure to 29.5 in Hg vacuum to bring the boiling point of water to 22°C (720°F). Atmospheric pressure (and vacuum gauge readings) decrease as altitude increases by approximately 25 mm (1 in) Hg per 3OOm (1OO0 ft). The following chart provides a guide to the various gauge readings at differing altitudes, for the same 1O mm (0.4 in) Hg absolute pressure.
Altitude ft Vacuum Reading in Hg
0 29.5
1,O0O 28.5
2,00O 27.4
3,000 26.4
4,000 25.4
5,000 24.5
6,000 23.5
7,000 22.6
8,000 21.8
9,000 2O.9
1O,000 2O.1
4. The low side gauge should indicate a vacuum of 660 mm (26 in) Hg within five minutes.
5. If 660 mm (26 in) Hg of vacuum is not achieved within five minutes, it signifies either the system has a leak or the vacuum pump is defective. Initially check the vacuum pump. if the pump proves to be functioning properly then investigate for a leak in the air conditioning system.
6. Continue evacuating for 30 minutes to ensure the removal of all moisture.
7. Stop the vacuum pump and allow the vacuum to hold for fifteen minutes, then check that there is no pressure rise (a loss of vacuum) evident on the compound gauge. Any pressure rise denotes a leak which must be rectified before proceeding further. Moisture remaining in the system will continue to boil and cause loss of vacuum.
8. With the system satisfactorily evacuated, the system is ready for charging with refrigerant.
CHARGE
CAUTION:
- Do not charge liquid refrigerant into the compressor. Liquid cannot be compressed; and if liquid refrigerant enters the compressor inlet valve, severe damage is possible; in addition, the oil charge may be absorbed into the refrigerant, causing damage when the compressor is operated.
- Do not overcharge the air conditioning system as this will cause excessive head pressure.
1. Ensure that the air conditioning system is evacuated.
2. Follow the equipment manufacturer's instructions for charging the system with refrigerant.
3. Ensure that the full charge of refrigerant 1.08 kg (38 oz) is drawn into the system.
4. After completing the procedure check the air conditioning system is operating satisfactorily by carrying out a pressure test, as described in this section.