Operation Characteristics In Relation To The Refrigerant Charge; Operation Check; Inspection And Maintenance - Mitsubishi Electric CITY MULTI PURY-P-ZKMU-A Installation Manual

11-3. Operation characteristics in relation to the refrigerant charge

It is important to have a clear understanding of the characteristics of refrigerant and the operation characteristics of air conditioners before
attempting to adjust the refrigerant charge in a given system.
・During cooling operation, the amount of refrigerant in the accumulator is the smallest when all indoor units are in operation.
・During heating operation, the amount of refrigerant in the accumulator is the largest when all indoor units are in operation.
・Refrigerant undercharge creates a tendency for the discharge temperature to rise.
・Changing the amount of refrigerant in the system while there is refrigerant in the accumulator has little effect on the discharge temperature.
・The higher the high pressure level, the more likely it is for the discharge temperature to rise.
・The lower the low pressure level, the more likely it is for the discharge temperature to rise.
・When the amount of refrigerant in the system is adequate, the compressor shell temperature is 10 to 60ºC (50 to 140ºF) higher than the low-
pressure saturation temperature. If the temperature difference between the compressor shell temperature and low-pressure saturation
temperature is 5ºC (41ºF) or less, refrigerant overcharge is suspected.

11-4. Operation check

The following symptoms are normal and do not indicate a problem.
Events
The auto vane automatically switches air flow direction.
The fan speed automatically changes during heating
operation.
The fan stops during heating operation.
The fan keeps running after the unit has stopped.
At the beginning of heating operation, the fan cannot be
manually set.
When the main power is turned on, the display as shown
right appears on the remote controller for about five
minutes.
The drain pump keeps running after the unit has
stopped.
The indoor unit emits noise when switching from heating
to cooling and vice versa.
Immediately after startup, the indoor unit emits the
sound of liquid flowing.

12. Inspection and maintenance

Only qualified personnel must relocate or repair the unit. Do not attempt to disassemble or alter the unit.
- Failure to do so will result in refrigerant leakage, water leakage, serious injury, electric shock, or fire.
・While the unit is turned on, the compressor will remain energized even when it is stopped. Before inspecting the inside of the control box, turn off
the power, keep the unit off for at least 10 minutes, and confirm that the capacitor voltage (inverter main circuit) has dropped to 20 VDC or less. (It
takes about 10 minutes to discharge electricity after the power supply is turned off.)
・Control boxes house high-voltage and high-temperature electrical parts. They may still remain energized or hot after the power is turned off.
・Perform the service after disconnecting the fan board connector (CNINV) and the inverter board connector (CN01, CN11).
(To plug or unplug connectors, check that the outdoor unit fan is not rotating and that the voltage of capacitor in the main circuit is 20 VDC or
below. The capacitor may collect a charge and cause an electric shock when the outdoor unit fan rotates in windy conditions. Refer to the wiring
nameplate for details.)
・Reconnect the connector (CNINV) back to the fan board and reconnect the connector (CN01, CN11) back to the inverter board after servicing.
・Unit components may be damaged after long use of the unit, resulting in a performance drop or the unit becoming a safety hazard. To use the unit
safely and maximize its life, it is recommended that a maintenance contract with a dealer or qualified personnel be signed. If the contract is
signed, service technicians will periodically inspect the unit to identify any damage at an early stage, and take appropriate measures.
WT07828X01
Display on remote Cause
controller
Normal display The auto vane may switch over to horizontal air flow operation from vertical air flow operation in cooling mode if
the vertical air flow operation has been running for one hour. At defrost in heating mode or immediately after
heating start-up/shutdown, the auto vane automatically switches to horizontal air flow for a short time.
Normal display The fan operates at Very Low speed when the thermostat is turned off, and automatically changes over to the
preset speed according to the timer setting or refrigerant temperature when the thermostat is turned on.
"Defrost" The fan remains stopped during the defrost cycle.
No display After the unit has stopped during heating operation, the fan operates for one minute to exhaust heat.
"Stand By" The fan operates at Very Low speed for five minutes after heating operation starts or until the refrigerant
temperature reaches 35°C (95°F), then the fan operates at Low speed for two minutes, and finally the fan
operates at the preset speed.
"HO" or "PLEASE The system is starting up. Wait until "HO" or "PLEASE WAIT" stops blinking and goes off then try again.
WAIT" blinks.
No display The drain pump remains in operation for three minutes after the unit in cooling mode has stopped.
The drain pump goes into operation when drain water is detected, even when the unit is stopped.
Normal display This is a normal sound of the refrigerant circuit operating properly.
Normal display Unstable flow of the heating medium produces a sound. This is temporary and does not imply a problem.
GB-36