High/Low Pressure Switch And Compressor Thermostat Circuits; Checking The Liner Expansion Valve (Lev); Mis-Wiring Or Mis-Piping - Mitsubishi Electric MXZ-18NV Service Manual

L High/low pressure switch and compressor thermostat circuits
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.
M Checking the liner expansion valve (LEV)
The outdoor control system stops due to abnormality.
<MXZ-18NV>
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-32NV>
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.
N Mis-wiring or mis-piping
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 finally gets damaged.
In the cooling operation, the compressor operates with liquid back, and finally gets damaged.
The other cases
O
1 In the case that the indoor fan and outdoor fan operate but the compressore does not operate,it causes that the high
pressure switch can be operated once.
First of all,check the high pressure switch can be shorted, turn OFF the power and turn ON again 1 minute later.
2 Indoor unit dose not operate.(different modes )
• When you try to run two indoor units simultaneously, one for cooling and the other for heating, the unit which transmits
signal to the outdoor units earlier decides the operation mode. The other unit indicates as shown in the figure below.
• When the above situation occurs, set all the indoor units to the same mode, turn OFF the indoor units, and then turn
them back ON.
• Thugh the top of the indoor unit sometimes gets warm, this does not mean malfunction. The reason is that the
refrigerant gas continuously flows into the indoor unit even while it is not operating.
OPERATION INDICATOR
48
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
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?
Lighting Frashing
Causes
Gas undercharged
Gas overcharged
Liner expansion valve
Ball valve
Indoor air filter clogged
No
Pipe length too long
Short cycle of outdoor air flow
Outdoor heat exchanger
(dust adherence)
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.
About 10 seconds after
start-up, does LEV
click?
No
No
Outdoor controller
board defective
HPS LPS
Yes
Normal
Yes
LEV defective
(+) (–)
Measuring
•RED-WHT
point
•RED-BLU
•RED-ORN
•RED-YLW
Compressor
thermistor