Midea V6R Series Manual page 107

V6R VRF 50/60Hz
5.10.2 Procedure
Notes for installers
During vacuum drying, a vacuum pump is used to lower the pressure in the piping to the extent that any moisture
present evaporates. At 5mmHg (755mmHg below typical atmospheric pressure) the boiling point of water is 0°C.
Therefore a vacuum pump capable of maintaining a pressure of -756mmHg or lower should be used. Using a vacuum
pump with a discharge in excess of 4L/s and a precision level of 0.02mmHg is recommended.
Caution
 Before performing vacuum drying, make sure that all the outdoor unit stop valves are firmly closed.
 Once the vacuum drying is complete and the vacuum pump is stopped, the low pressure in the piping could suck
vacuum pump lubricant into the air conditioning system. The same could happen if the vacuum pump stops
unexpectedly during the vacuum drying procedure. Mixing of pump lubricant with compressor oil could cause
compressor malfunction and a one-way valve should therefore be used to prevent vacuum pump lubricant
seeping into the piping system.
Procedure
The vacuum drying procedure is as follows:
Step 1
 Connect the vacuum pump through a manifold with a pressure gauge to the master unit's all stop valves.
Step 2
 Start the vacuum pump and then open the manifold valves to start vacuuming the system.
 After 30 minutes, close the manifold valves.
 After a further 5 to 10 minutes check the pressure gauge. If the gauge has returned to zero, check for leakages in
the refrigerant piping.
Step 3
 Re-open the manifold valves and continue vacuum drying for at least 2 hours and until a pressure difference of
756mmHg or more has been achieved. Once the pressure difference of at least 756mmHg has been achieved,
continue vacuum drying for 2 hours.
Step 4
 Close the manifold valves and then stop the vacuum pump.
 After 1 hour, check the pressure gauge. If the pressure in the piping has not increased, the procedure is finished.
If the pressure has increased, check for leakages.
 After vacuum drying, keep the manifold connected to the master unit stop valves, in preparation for refrigerant
charging. (see Part 3, 8 "Charging Refrigerant").
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Figure 3-5.14: Vacuum drying