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Haier 2U18MS2VHB Service Manual page 23

Ductless multi-split heat pump, outdoor/indoor, wall mount - highwall, 2'x2' compact cassette, 3'x3' large cassette, slim duct, mid-static ducted, medium static ducted, console
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Temperature Sensor Td
The temperature of the compressor discharge hot gas will
be monitored by the Discharge Temperature Sensor. If the
sensor reads too hot or cool, the frequency/status of the
operation will potentially be altered.
The hot gas will leave the oil separator and enter the 4 way
valve. The 4 way valve will direct the hot gas to ALL of the
indoor coils.
Note: Any indoor unit that is in heating mode will have it's
louver open and indoor fan running. Non-calling indoor units
will receive hot gas but their fans will remain on very low speed
with the louver open. When demand for heat increases, the
indoor fan will speed up to meet the increased demand.
Temp. Sensor Tc1 & Indoor Heat Exchanger Temp. Sensor
The temperature of Tc1 should now be hot. This will indicate
the 4 way valve is directing hot gas to the indoor coils. If it
is not, there is a problem with the 4 way valve. The ECU will
detect the temperature difference and generate an Error
The indoor heat exchanger temperature sensor will monitor
the temperature of the indoor coil to ensure it is hot
enough to prevent blowing cold air. Once adequately warm
temperature is sensed at the indoor coil, the ECU will energize
the indoor fan to a higher speed.
The hot gas entering the indoor coil will condense into a
saturated mix and then be subcooled. The refrigerant will
return to the outdoor unit via the mixed phase small line.
Temperature Sensor Tc2
This sensor monitors the temperature of the refrigerant liquid
returning from the indoor coil. If abnormally warm liquid is
sensed, the ECU will make inverter or indoor fan motor speed
changes to compensate.
The liquid will enter the Liquid Line Strainer and will pass
through the OPEN EEV The refrigerant liquid now enters a
receiver where excess refrigerant will store.
After the liquid leaves the Liquid Receiver, it will enter the
restriction of the OUTDOOR UNIT's EEV. The EEV will drop
the pressure of the liquid to low pressure low temperature.
Heat from the outdoor air will boil off the cold refrigerant.
The outdoor coil absorbs heat from the outdoor air. The
refrigerant vapor boiling from the liquid refrigerant in the
outdoor coil exits the outdoor coil.
The outdoor coil temperature will be sensed by the Defrost
Sensor. The sensor will use this temperature to maintain
EEV position/superheat adjustment and to calculate when a
defrost cycle is necessary.
This temperature sensor is now sensing the suction line
temperature of the refrigerant vapor leaving the outdoor
coil. This temperature is used in calculation of the required
position of the OUTDOOR UNIT EEV for proper superheat
The vapor refrigerant will then enter the 4 way valve and
be directed to the Compressor suction accumulator. The
accumulator will trap any liquid refrigerant that may enter the
compressor and potentially damage it.
The vapor will exit the accumulator and enter the
compressor. The refrigeration cycle will continually repeat
until the demand for heating ends.
The temperature of the suction gas entering the compressor
is monitored by the Suction Temperature Sensor. If abnormal
temperature either hot or cool is detected, the frequency
of the compressor may be adjusted or the system may stop
operation to protect the compressor.
During the call for heating, the indoor air temperature will
get closer to setpoint and demand will ease. The compressor
will reduce frequency as the demand decreases. Should
an additional indoor unit call for heating, the demand will
increase and the compressor speed will increase.
When the temperature setpoint of the indoor units is met, the
indoor units will continue to run but the outdoor unit will shut
off. This is normal operation.
Temperature Sensor Te
Temperature Sensor Toci
Temperature Sensor Ts

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