Mitsubishi Electric MUH-GA50VB-E1 Service Manual page 31

Unit operates COOL mode even if it is set to HEAT mode.
Check of R.V. coil
C
w First, measure the resistance of R.V. coil to confirm it is disconnected or is not short-circuit.
Disconnect the TAB52 on the deicer P.C. board. (MUH-GA60/GA80VB)
Turn ON the power supply and operate the indoor unit in HEAT mode
by pressing the EMERGENCY OPERATION switch.
When OPERATION INDICATOR lamp flashes ON and OFF in every 0.5-second.
Outdoor unit doesn't operate.
How to check mis-wiring
D
Yes
Correct them.
1. Turn OFF the power supply (indoor/ outdoor unit) and disconnect indoor/outdoor
connecting wire on indoor side.
2. Short-circuit terminal block N-3 by lead wire.
3. Turn ON the power supply (indoor unit) and press EMERGENCY OPERATION switch once.
Is there 5V DC between J205 + -J101 - (MUH-GA50VB)/
J101 + -J401 - (MUH-GA60/GA80VB) on the deicer P.C.
board?(Refer to 10-5.)
After 3 minutes, does the unit
operate in COOL mode?
Yes
Is there 230V AC between
CN7211 – 2 (MUH-GA50VB)/
CN7211 – 3 (MUH-GA60/GA80VB)
on the deicer P.C. board?
Yes
Replace the R.V. coil.
Start
• Turn ON the power supply. (indoor/ outdoor unit)
• Press EMERGENCY OPERATION switch once.
After 3 minutes, mis-wiring is indicated
(0.5-second ON, 0.5-second OFF)
on OPERATION INDICATOR
lamp on indoor unit.w
Is this mis-wiring, poor contact,
or wire disconnection?
No
Is there 20V DC between both ends of
R132 on the indoor electronic control P.C.
board ?
( By tester, the stylus is between 0 ~ 20V. )
Yes
• Turn OFF the power supply. (indoor unit)
• Connect indoor/ outdoor connecting
wire.
Turn ON the power supply. (outdoor unit)
Is there 230V AC between L-N
on the outdoor terminal block?
Yes
Yes
During EMERGENCY OPERATION, is there
10V DC between both ends of R601 on the
deicer P.C. board? (Refer to 10-5.)
(By tester, the stylus is between 5 ~10V.)
Yes
Replace the deicer P.C. board.
No
OK
No
Replace the
deicer P.C. board
w Short circuit of JPG and JPS on the indoor electronic control
P.C. board enables self -check to be displayed in 3 seconds.
No
Replace the indoor electronic
control P.C. board.
No
Check the outdoor power supply
and connection of wiring.
No
Replace the deicer P.C. board.
Make the wiring between CN730
No
on the deicer P.C. board and
outdoor terminal block correct.
(Refer to 10-5.)
31
Refer to indoor unit
service manual.