Mitsubishi Electric PLA-A12EA8 Service Manual page 27

9-6-1. Thermistor
<Thermistor characteristic graph>
Thermistor for
lower temperature
Thermistor R =15 k" ± 3%
0
Fixed number of B=3480 ± 2%
t(:)Rt=15exp { 3480(
T(˚F)Rt=15exp { 3480(
32˚F [0:]
50˚F [10:]
68˚F [20:]
77˚F [25:]
86˚F [30:]
104˚F [40:]
9-6-2. DC fan motor (fan motor/indoor controller board)
Check method of DC fan motor (fan motor/indoor controller circuit board)
Notes
1
· High voltage is applied to the connecter (CNMF) for the fan motor. Pay attention to the service.
· Do not pull out the connector (CNMF) for the motor with the power supply on.
(It causes trouble of the indoor controller circuit
Self check
2
Symptom : The indoor fan cannot rotate.
Check the fuse (FUSE) on indoor
controller board.
Did the fuse blow?
No
Wiring contact check
Contact of fan motor connector (CNMF)
Is there contact failure?
No
Power supply check (Remove the connector (CNMF))
Measure the voltage in the indoor controller circuit
TEST POINT
1 : V (between 1 (+) and 4 (−) of the fan connector): V
DC
TEST POINT 2 : V (between 5 (+) and 4 (−) of the fan connector): V
CC
Is the voltage normal?
No
Replace the indoor
controller board.
Check the operation.
Fail
Replace the defective fan motor.
TCH120A
Room temperature thermistor(TH1)
Pipe temperature thermistor/liquid(TH2)
Condenser/evaporator temperature
thermistor(TH5)
1 1
) }
273+t 273
1 1
) }
T-32
273+ 273
1.8
15 k"
9.6 k"
6.3 k"
5.4 k"
4.3 k"
3.0 k"
board and fan motor.)
Check the drain pump (DP).
Yes
Is the resistance between
terminals normal?
Replace the drain pump (DP).
Yes
Correct wiring.
board.
Yes
Replace the defective fan motor.
Check the operation of fan.
Replace the indoor controller board.
OK
Complete.
50
40
30
20
10
Yes
No
294–325 V DC
DC
15 V DC
CC
Yes
OK
Fail
27
<Thermistor for lower temperature>
0
20 10 0 10 20 30 40 50
− −
4 14 32 50 68 86 104122
− −
Temperature
Replace the indoor controller board (I.B).
Replace the defective fan motor (MF).
Complete.
:
°F