Mitsubishi Electric MSZ-FD VA Series Service Manual page 44

MUZ-FD50
• Heating operation does not work.
1. Disconnect the lead wire leading to the compressor.
2. 3 minutes after turning on the power supply, start EMERGENCY
OPERATION in HEAT mode.
Is there voltage of 230 VAC between pin1 and
pin 2 at connector CN912?
Yes
Turn OFF power supply of indoor and outdoor unit.
Disconnect the connec-
tor CN912 in noise fi lter
P.C. board. Is there normal
resistance to R.V. coil?
Yes
Replace the 4-way valve.
• Cooling operation does not work.
1. Disconnect the lead wire leading to the compressor.
2. 3 minutes after turning on the power supply, start EMERGENCY
OPERATION in COOL mode.
Is there voltage of 230 VAC between pin1 and
pin 2 at connector CN912?
1. Turn OFF power supply of indoor and outdoor unit, and
disconnect the connector CN781 in the outdoor electronic
control P.C. board.
2. 3 minutes after turning ON the power supply, start EMER-
GENCY OPERATION in COOL mode.
Is there voltage 12 VDC between the connector
CN781 pin 5 (+) and pin 3 (-)?
Replace the outdoor electronic control P.C. board.
No
Replace the R.V. coil.
No
Yes
1. Turn off power supply of indoor and outdoor unit, and discon-
nect the connector CN781 in the outdoor electronic control P.C.
board.
2. 3 minutes after turning ON the power supply, start EMER-
GENCY OPERATION in HEAT mode.
Is there voltage 12 VDC be-
tween the connector CN781
pin 5 (+) and pin 3 (-)?
Yes
Replace the noise fi lter P.C. board.
Replace the 4-way valve.
No
Replace the noise fi lter P.C. board.
No
44
Replace the outdoor
electronic control P.C.
No
board.
If the connector CN912 is disconnected or
R.V. coil is open, voltage occurs between
terminals even when the control is OFF.