Mitsubishi Electric CITY MULTI PUHY-400YMF-B Service Handbook page 115

(4) Heating operation
Variable capacity unit
1. Inverter output 0 Hz
2. Indoor unit LEV, SLEV,
LEV1 full closed
3. All solenoid valve OFF
4. Outdoor unit fan stop
5. 52C2 OFF
6. F = 0 after 6 minutes 52C1 OFF
Constant capacity unit
1. 52C OFF
2. Outdoor unit fan stop
3. LEV1, LEV2 full closed
4. All solenoid valves
closed
Note: 1 When the outdoor unit goes into defrost operations, a defrost operation command is sent to the indoor unit.
Once the signal is received by the indoor unit, it too begins defrost operations. Defrost operation termination works in the
same manner, with the indoor unit switching to heating operations after receiving the defrost operation termination com-
mand from the outdoor unit.
Note: 2 Conditions for defrost termination: After 15 minutes of defrost operations, or when the outdoor unit coil temperature is above
7°C.
Note: 3 Even when the constant capacity unit is stopped, the fan and the solenoid valves LEV1, LEV2 are sometimes operated.
Heating operation
Note: 1
Defrosting
operation
4-way valve ON
Test run start
NO
NO
Thermostat ON
YES
YES 3-minute
restart pre-
vention
NO
Variable capacity unit
1. Inverter frequency level control
2. Indoor LEV, SLEV, LEV1 control
3. Solenoid valve control
4. Outdoor unit fan control
5. 52C1, 52C2 control
NO
Constant
capacity unit
operation
NO
Note: 3
Constant capacity unit
1. 52C OFF
2. Outdoor unit fan stop
3. All solenoid valves
closed
4. LEV1, LEV2 full closed
capacity unit operation or
Operation over 30 minutes before
stopping the constant
YES
Variable capacity unit 4-way valve OFF
Constant capacity unit 4-way valve ON
1. Indoor unit fan stop.
2. Indoor unit LEV full open.
Variable capacity unit
1. Inverter frequency at defrost control
2. LEV1, SLEV control
3. Solenoid valve control
4. Outdoor unit fan control
5. 52C1, 52C2 control
Constant capacity unit
1. 52C ON
2. Outdoor unit fan control
3. Solenoid valve control
4. LEV1, LEV2 control
YES
Constant capacity unit
1. 52C ON
2. Outdoor unit fan control
3. Solenoid valve control
4. LEV1, LEV2 control
–112–
Normal operations
Defrosting operations
Stop
Test run
During constant
NO
capacity unit.
YES
Variable capacity unit 4-way valve OFF
Constant capacity unit 4-way valve ON
1. Indoor unit fan stop.
2. Indoor unit LEV full closed.
Variable capacity unit
1. Inverter frequency at defrost control
2. LEV1, SLEV control
3. Solenoid valve control
4. Outdoor unit fan control
5. 52C1, 52C2 control
Constant capacity unit
1. 52C OFF
2. Outdoor unit fan control
3. All solenoid valves OFF
4. LEV1, LEV2 full closed
Note: 2
Defrosting
operation
YES
Terminate
defrost
Return to heating
operations
NO