Operation Characteristics In Relation To The Refrigerant Charge; Operation Check - Mitsubishi Electric CITY MULTI PUHY-P72TNU-A-B Manuel D'installation

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
A specific indoor unit is not performing the
cooling or heating operation.
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 refrigerant flowing.
Warm air comes from an indoor unit that
is not performing the heating operation.
Drain water comes out of the outdoor unit
from the bottom part of the heat
exchanger.
WT09452X01
Display on Cause
remote
controller
"Cool" or "Heat" Other indoor units in the same refrigerant system are already operated in a
blinks. different mode.
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 The system is starting up. Wait until "HO" or "PLEASE WAIT" stops blinking and
"PLEASE WAIT" goes off then try again.
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 refrigerant produces a sound. This is temporary and does not
imply a problem.
Normal display The LEV is slightly open for preventing any refrigerant, inside of the indoor unit that
is not performing the heating operation, from being liquefied. This does not imply a
problem.
No display This ensures proper drainage of drain water in case the drain water freezes and
remains in the outdoor unit during the heating operation at low ambient
temperature.
GB-60