Check Of Hi/Low Pressure Switch And Compressor Thermostat Circuits; Check Of Liner Expansion Valve (Lev); Check Of Mis-Wiring Or Mis-Piping - Mitsubishi Electric MSC-07RV Service Manual

Check of hi/ low pressure switch and compressor thermostat circuits
R
No heating/cooling
•Three minutes after the
unit stops, check that
the high and low pressure
switch open and close
properly.
•After the unit stops,
remove the sound-proof
material around the
compressor.
•60 minutes after that,
check that the
compressor thermostat
opens and closed
properly.

Check of liner expansion valve (LEV)

S
The outdoor control system stops due to abnormality.
<MXZ-18RV>
Turn OFF the power supply and make sure that LEDs
on outdoor electronic control P.C. board turn OFF.
Then turn ON power supply.
<MXZ-32RV>
Turn off the breaker
CN605
and short-circuit
pin1 and pin3 at
Short-
CN605 on the out-
circuit
door control board.
Operation status
Indoor unit:Normal
Outdoor unit:Compressor and outdoor
fan stop running and LEV closes
repeatedly.

Check of mis-wiring or mis-piping

T
Incorrect connection of indoor units results in no cooling/heating. In the all unit operation, however, the system seems to
operate normally even if wires or pipes are connected incorrectly.
Therefore, use the single-unit operation, not the all-unit operation, to check mis-wiring or mis-piping.
<Check of mis-wiring or mis-piping>
The following symptoms appears if wires or pipes are wrongly connected.
In the single-unit operation in HEAT mode, the compressor stops due to high pressure protection or it operates at the lowest
frequency at the normal working temperature, causing no heating.
In the single-unit operation in COOL mode, the indoor unit blows out air but it is not cooling, causing no cooling. The heat
exchanger freezes in non-operating unit(s).
<EFFECT>
In the heating operation, the compressor stops and restarts operation too frequency due to high pressure protection, and final-
ly gets damaged.
In the cooling operation, the compressor operates with liquid back, and finally gets damaged.
Yes
High/low pressure switch,
Open status
compressor or refrigerant
circuit defective.
No
Turn on power to the outdoor unit and
press the emergency switch for cooling
or heating operation.
Right after compressor start-up, does the
LED indication appear to show the low-
speed-operation due to high/low switch
protection?
Yes
Outdoor controller board defective
LEV operates for the first 30 seconds after power supply is turned ON.
While LEV is operating, check that there is 12V DC pulse amplitude between both
ends oh LEV diode. Repeat this for 4 diodes each in unit A and B.
•When no pulse amplitude, the outdoor electronic control P.C. board is defective.
•When checking, LEV connectors must be connected.
Turn on the breaker
and operate the air
conditioner with
the remote controller.
Disconnect the LEV relay connector and check the voltage at the following
points between terminals on the controller board side. Does the voltage
fluctuate between 7.5 and 8.5V DC at any points?
<Only MXZ-18RV>
Causes
Gas undercharged
Gas overcharged
Liner expansion valve
Ball valve
Indoor air filter clogged
Pipe length too long
Short cycle of outdoor air flow
No
Outdoor heat exchanger
(dust adherence)
<MXZ-18/32RV>
About 10 seconds after
start-up, does LEV
click?
No
No
Outdoor controller
board defective
140
<MXZ-18/32RV>
LPS
HPS
(MXZ-32)
Yes
Normal
Yes
Measuring
Compressor
thermistor
LEV defective
(+) (–)
•RED-WHT
point
•RED-BLU
•RED-ORN
•RED-YLW