Page 21
2-Crankcase Heaters HR1 and HR2
All LHT units use insertion type heaters. Heater HR1 is
installed around compressor B1 and HR2 compressor B2.
3-High Pressure Switches S4 and S7
The high pressure switches is an auto-reset SPST N.C.
switch which opens on a pressure rise. All units are
equipped with this switch. The switch is located in the
compressor discharge line and is wired in series with the
compressor contactor coil through A55 unit controller or
S4 and S7 are is wired in series with B1 and B2 compres-
sor contactors.
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ing a problem in the system) the switch opens and the re-
spective compressor(s) is de-energized (the economizer
can continue to operate). When discharge pressure drops
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ing the compressor(s).
Main control A55 has a three-strike counter before lock-
ing out. This means the control allows three high pressure
trips per one thermostat demand. The control can be reset
by breaking and remaking the thermostat demand or man-
ually resetting the control
4-Low Pressure Switches S87 and S88
The low pressure switch is an auto-reset SPST N.O.
switch (held N.C. by refrigerant pressure) which opens on
a pressure drop. All units are equipped with this switch.
The switch is located in the compressor suction line. See
with the contactor coils through the A55 Unit Controller
The Unit Controller A55 governs the low pressure switch-
es by shunting the switches during start up until pressure
before the compressor(s) is locked out. The control is re-
set by breaking and remaking the thermostat demand or
manually resetting the control.
When suction pressure drops to 40 + 5 psig (indicating
de-energized. The switch automatically resets when pres-
sure in the suction line rises to 90 + 5 psig.
5-Defrost Control
The defrost control ensures that the heat pump outdoor
defrost control uses input from the coil and ambient sen-
sor to initiate demand defrost cycles from the M4 Board. If
the system fails to calibrate or obtain readings for demand
(LHT) or electric heat (LHT) is energized during defrost.
6-Filter Drier (all units)
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er removes contaminants and moisture from the system.
7-Condenser Fans
B4, B5, B21, B22, B23 and B24 (All Units)
See SPECIFICATIONS tables at the front of this manual
condenser fans used have single-phase motors. The fan
assembly may be removed for servicing and cleaning.
8-Reversing Valve
A refrigerant reversing valve with a 24 volt solenoid coil
in all LHT units. The reversing valve is connected in the
vapor line of the refrigerant circuit. The reversing valve coil
is energized during cooling demand and during defrost.
board in response to a cooling demand or by defrost.
9-Temperature Thermistor
Units are equipped with four factory-installed thermistors
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ant circuit.
The thermistors provide the Unit Controller with constant
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frigeration circuit. These temperatures are used as feed-
Unit Controller uses these temperatures to initiate alarms
charge.
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