Midea MSMBB-12CRDN1-MP0W Service Manual page 17

Procedure
With the unit in the cooling mode and a low set
1).
point remove all caps from the 3 way and 2 way
valves, next attach the low pressure gauge to the 3
way service valve port and purge the air from that
hose by loosening the hose at the manifold for a
second, be sure the low pressure gauge valve is
closed. be sure to record the operating
pressure, you will need to know this when you
complete the service on the indoor unit and restart
the system. Now prepare to close both valves on
the unit starting with the 2 way valve (this is called
front seating the valve) also prepare to shut the
power off to the outdoor unit.
2). Connect the charge hose with the push pin
of handle lo to the 3-way valves gas service
port.
3). Air purging of the charge hose.
Open the handle Lo valve of the manifold valve
slightly to purge air from the charge hose for 5
seconds and then close it quickly.
Now close the 2 way valve and monitor the low
4).
pressure gauge. the pressure will start to drop.
Operate the unit in the cooling mode and
5).
disconnect the power to the outdoor unit when the
low side gauge reads a slight vacuum, running the
compressor in a vacuum could damage the motor
windings. Note that units with extended lines and
additional refrigerant charge may not be able to
achieve a vacuum, this
unit can only store a certain amount of refrigerant,
this is normal (the amperage of the compressor
will have to be monitored in this case) Stop
compressor when the amperage approaches the
name plate FLA rating
Now close the 3 way valve right away. the
6).
is because the outdoor
indicates 0.1Mpa(14.5Psi).
pressure will rise during this time, this is normal.
There will be some pressure left in the system this
is normal, The indoor unit is now ready to be
serviced.
Disconnect the charge set, and tighten the
2-way and 3-way valve's stem nuts.
Use a torque wrench to tighten the 3-way valves
service port cap to a torque of 18N.m(
ft.lbs
).
Be sure to check for gas leakage.
Sweeping (air purging) the system with
2.
refrigerant after the service to the
refrigerant circuit of the indoor unit is
complete.
Procedure:
Sweeping the system can be used when the unit
has been pumped down, this eliminates the need
to loosen the flare connection on the 2 way valve
(loosening and retightening flare connections
could cause a refrigerant leak)
1). Confirm that both the 2-way and 3-way
valves are set to the closed position.
2). Connect the charge set and a charging
cylinder to the service port of the 3-way valve
Leave the valve on the
Do not loosen the flare connection, Start with
3).
the hose from the low pressure gauge that has
been connected to the 3 way valve service port
and loosen it at the gauge manifold connection,
next open the 2 way valve 1/2 half of a turn (this
will release the refrigerant that has been isolated in
the outdoor unit) The refrigerant will travel thru
the small refrigerant line and evaporator coil in the
indoor unit and back out the low pressure hose
that has been loosened let the refrigerant sweep
for about 50 seconds, this will push and remove
15
= 13.27
Refrigerant container
.