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Haier 2U18MS2VHB Service Manual page 21

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 the outdoor
coil. The refrigerant will condense in the outdoor coil and be
slightly subcooled. The refrigerant is now in a liquid state.
Temperature Sensor Toci
The temperature of the hot gas leaving the 4 way valve will be
monitored by the Toci Temperature Sensor. This temperature
should be near the temperature of the compressor discharge
gas temperature. If it is not, there is a problem with the 4 way
valve. The ECU will detect the temperature difference and
generate an Error Code.
Temperature Sensor Tc
This sensor monitors the temperature of the outdoor
coil during condensing operation. If abnormal condensing
temperature is detected this sensor, the outdoor fan motor
speed or compressor frequency may be adjusted.
Temperature Sensor Ta
The outdoor air temperature will be monitored by the ECU.
If the outdoor air temperature rises or falls, the speed of the
outdoor fan/positions of the EEV's may be changed.
The refrigerant liquid will exit the outdoor coil and enter a
strainer where debris is trapped. The refrigerant liquid leaves
the strainer and bypasses the outdoor coil EEV via a path
through the check valve.
The refrigerant liquid now enters a receiver where excess
refrigerant will store. The required liquid leaves the outdoor
liquid receiver and passes through the Liquid Stop Valve.
After the liquid leaves the stop valve, it will enter the
restriction of the CALLING INDOOR UNIT's EEV. The EEV
will drop the pressure of the liquid to low pressure low
Temperature Sensor Tc2
The EEV associated Liquid Pipe Sensor will monitor the
temperature of the refrigerant leaving the EEV to calculate
system superheat.
The low pressure low temperature refrigerant will enter the
mixed phase liquid line and travel to the indoor unit. Heat from
the air passing across the indoor unit evaporator will flash off
the cold refrigerant into a cold vapor.
The cold vapor will travel down the vapor line and return to the
outdoor unit via a path through the Gas Stop Valve.
The EEV Gas Pipe Sensor will monitor the temperature of the
suction gas to calculate the difference between Liquid Pipe
Temperature and Gas Pipe Temperature. This calculation is
the suction vapor superheat. If a change in EEV port opening
size is needed, the EEV will make a small adjustment.
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 cooling 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 cooling, 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 cooling, 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 Tc1
Temperature Sensor Ts

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