6O 7O
SUCTION LINETEMPERATURE,
Fig. 20 - Cooling Charging Chart, 50ZH048 Units
C00166
SUCTION LINE TEMPERATURE
C00167
Fig. 21 - Cooling Charging Chart, 50ZH060 Units
Step 5 -- Unit Controls
All compressors have the following internal-protection controls.
HIGH-PRESSURE RELIEF VALVE
This valve opens when the pressure differential between the low
and high side becomes excessive. (024 size has temperature relief
only).
LOSS OF CHARGE SWITCH
Located on the outdoor liquid line is a low-pressure switch which
functions as a loss-of charge switch. This switch contains a
Schrader core depressor. This switch opens at 7 psig and closes at
22 psig. No adjustment is necessary.
COMPRESSOR OVERLOAD
This overload interrupts power to the compressor when either the
current or internal temperature become excessive, and
automatically resets when the internal temperature drops to a safe
level. This overload may require up to 60 minutes (or longer) to
reset; therefore, if the internal overload is suspected of being open,
disconnect the electrical power to the unit and check the circuit
through the overload with an ohmmeter or continuity tester.
Step 6 -- Sequence of Operation
FAN OPERATION -- The FAN switch on the thermostat controls
indoor fan operation. When the FAN switch is placed in the ON
position, the IFR (indoor-fan relay) is energized through the G
terminal on the thermostat. The normally-open contacts close,
which then provide power to the indoor (evaporator) fan motor
(IFM). The IFM will run continuously when the FAN switch is set
to ON.
When the FAN switch is set to AUTO, the thermostat deenergizes
the IFR (provided there is not a call for cooling). The contacts open
and the IFM is deenergized. The IFM will be energized only when
there is a call for cooling.
NOTE: Some units are equipped with a time-delay relay. On
these units, the indoor fan remains on for 30 seconds after G or Y
is deenergized.
COOLING
With the thermostat subbase in the cooling position, the thermostat
makes circuit R-). This energizes the reversing valve solenoid
(RVS) and places the unit in standby condition for cooling.
NOTE: The defrost control board has a 5 minute compressor
anti-short cycle time delay built in between compressor starts.
On a call for cooling, the compressor contactor (C) and the IFR are
energized through the Y and G terminals of the thermostat.
Energizing the compressor contactor supplies power to the
compressor and the outdoor (condenser) fan motor (OFM).
Energizing the IFR provides power to the IFM.
When the need for cooling has been satisfied, the OFM,
compressor, and IFM (FAN on AUTO) are deenergized. If the unit
is equipped with a 30-second delay (036 size only), the indoor fan
will remain energized for 30 seconds after the compressor is
deenergized. The reversing valve solenoid remains energized.
HEAT PUMP HEATING
On a call for heat, thermostat makes circuits R-Y and R-G. When
compressor time delay (5-minute 2 minutes) is completed, a circuit
is made to C. Starting COMP and OFM. Circuit R-G also
energizes IFR and starts IFM after I-second delay.
When thermostat is satisfied, contacts open, deenergizing contactor
and relay; motors deenergize. The IFM may be controlled by a
time-delay relay that keeps the fan on for 30 seconds.
DEFROST
Defrost board (DB) is a time and temperature control, which
includes a field-selectable time period between checks for defrost
(30, 50 and 90 minutes). The time period is factory-set at 60
minutes and should only be adjusted by a trained service person.
Electronic timer and defrost cycle start only when contactor is
energized and defrost thermostat (DFT) is closed.
Defrost mode is identical to Cooling mode. The outdoor fan motor
stops because of "OFI" and OF2" contacts opening on the defrost
board.
13
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