Mitsubishi Electric PLA-RP50 Service Manual download pdf (Page 21)

10-3. SELF-DIAGNOSIS ACTION TABLE

Note: Refer to the manual of outdoor unit for the details of display

such as F, U, and other E.

Error Code

Abnormal point and detection method

Cause

Countermeasure

Room temperature thermistor (TH1)

1 The unit is in 3-minute resume

prevention mode if short/open of

thermistor is detected. Abnormal if the

unit does not reset normally after 3 min-

utes. (The unit returns to normal opera-

tion, if it has been reset normally.)

2 Constantly detected during cooling,

drying, and heating operation.

Short: -90: or more

Open: -40: or less

1 Defective thermistor

characteristics

2 Contact failure of connector

(CN20) on the indoor controller

board (Insert failure)

3 Breaking of wire or contact

failure of thermistor wiring

4 Defective indoor controller

board

1–3 Check resistance value of thermistor.

0: 15.0k"

10: 9.6k"

20: 6.3k"

30: 4.3k"

40: 3.0k"

If you put force on (draw or bend) the lead wire

while measuring resistance value of thermis-

tor, breaking of wire or contact failure can be

detected.

2 Check contact failure of connector (CN20)

on the indoor controller board. Refer to 10-7.

Turn the power on again and check restart

after inserting connector again.

4 Check room temperature display on remote

controller.

Replace indoor controller board if there is

abnormal difference with actual room

temperature.

Turn the power off, and on again to operate

after check.

Pipe temperature thermistor/Liquid

(TH2)

1 The unit is in 3-minute resume

prevention mode if short/open of

thermistor is detected. Abnormal if the

unit does not reset normally after 3 min-

utes. (The unit returns to normal opera-

tion, if it has been reset normally.)

2 Constantly detected during cooling,

drying, and heating (except defrosting)

operation

Short: 90: or more

Open: -40: or less

1 Defective thermistor

characteristics

2 Contact failure of connector

(CN44) on the indoor controller

board (Insert failure)

3 Breaking of wire or contact

failure of thermistor wiring

4 Defective refrigerant circuit is

causing thermistor temperature

of 90: or more or -40: or

less.

5 Defective indoor controller

board

1–3 Check resistance value of thermistor.

For characteristics, refer to (P1) above.

2 Check contact failure of connector (CN44)

on the indoor controller board. Refer to 10-7.

Turn the power on and check restart after

inserting connector again.

4 Check pipe <liquid> temperature with remote

controller in test run mode. If pipe <liquid>

temperature is extremely low (in cooling

mode) or high (in heating mode), refrigerant

circuit may have defective.

5 Check pipe <liquid> temperature with

remote controller in test run mode. If there is

extremely difference with actual pipe <liquid>

temperature, replace indoor controller board.

Turn the power off, and on again to operate

after check.

Contact failure of drain float switch

(CN4F)

• Extract when the connector of drain float

switch is disconnected.

(3 and 4 of connector CN4F is not

short-circuited.)

• Constantly detected during operation

1 Contact failure of connector

(Insert failure)

2 Defective indoor controller

board

Check contact failure of float switch connector.

Turn the power on again and check after

inserting connector again.

2 Operate with connector (CN4F) short-

circuited.

Replace indoor controller board if abnormality

reappears.

Drain over flow protection operation

1 Suspensive abnormality, if drain float

switch is detected to be underwater for

1 minute and 30 seconds continuously

with drain pump on.

Compressor and indoor fan will be

turned off.

2 Drain pump is abnormal if the condition

above is detected during suspensive

abnormality.

3 Constantly detected during drain pump

operation

1 Malfunction of drain pump

2 Defective drain

Clogged drain pump

Clogged drain pipe

3 Defective drain float switch

Jamming of the drain float

switch or malfunction of mov-

ing parts causing the drain float

switch to be detected under

water (Switch On)

4 Defective indoor-controller

board

1 Check if drain pump works.

2 Check drain function.

3 Remove drain float switch connector CN4F

and check if it is short (Switch On) with the

moving part of float switch UP, or OPEN with

the moving part of float switch down.

Replace float switch if it is short with the

moving part of float switch down.

4 Replace indoor controller board if it is short-

circuited between 3-4 of the drain float

switch connector CN4F and abnormality

reappears.

It is not abnormal if there is no problem about

the above-mentioned

Turn the power off, and on again to operate

after check.

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Mitsubishi Electric PLA-RP50 Service Manual Page 21

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