21 PB
Compressor Delay Time
A change of reversing valve state will shut off the compressor at the start of a defrost cycle for the rst 30 seconds of defrost
operation. At the end of the defrost cycle, the compressor will be shut off prior to changing the reversing valve state. Following a 30
second delay, the compressor will be turned back on. I
Cooling
When powering unit for the rst time there is a time delay of 3 minutes. The thermostat energizes the Y terminal at the defrost
control board. The defrost control board will send 24 VAC out cc to energize the contactor; L1 to T1 on the contactor providing power
to the compressor and the outdoor condenser motor.
If the control has “Y” thermostat input present without a “B” input, the compressor output should be active (once the ASCD has
expired), and the condenser fan relay contacts should remain closed.
Low Pressure Switch Operation (Cooling)
Normally Closed. Opens at 30 psig and closes at 50 psig.
If the Low Pressure switch opens during cooling operation, the compressor contactor will be de-energized and the ASCD will be
reset. During the period with a low pressure switch open, the “Low Pressure Switch Open” fault condition will be displayed as
described in Table 502.
High Pressure Switch Operation (Cooling)
Normally Closed. Open At 675 Psig And Close At 475 Psig.
If the High Pressure switch opens during cooling operation, the compressor contactor will be de-energized and the ASCD will be
reset. During the period with a high pressure switch open, the “High Pressure Switch Open” fault condition will be displayed as
described in section Table 502. If three High Pressure Switch faults happen within the same call for cooling, the control will lockout
the compressor and display the “High Pressure Switch Lockout” fault condition will be displayed as described in Table 502. If the “Y”
thermostat demand is removed, the counter that keeps track of the three pressure switch trips will be reset.
Heating
Heating is same as cooling except thermostat sends B signal to defrost control board which energizes the reversing valve solenoid.
A safety relay is incorporated into the design of the system to prevent emergency heat and the compressor from running
simultaneously. Thermostat should not send a B and W2 signal at the same time, however if that happens then W2 will break the
signal to defrost control board through the safety relay.
If the control has recognized both “Y” and “B” thermostat inputs present, the compressor contactor should be active (once the ASCD
has expired), and the condenser fan relay contacts should remain closed.
Low Pressure Switch Operation (Heating)
Normally Closed. Opens at 30 psig and closes at 50 psig.
If the Low Pressure switch opens during heating operation, the compressor contactor will be de-energized and the ASCD will be
reset. During the period with a low pressure switch open, the “Low Pressure Switch Open” fault condition will be displayed as
described in Table 502.
If three Low Pressure Switch faults happen within a 120 minute period and within the same call for heating, the control will lockout
the compressor and display the “Low Pressure Switch Lockout” fault condition will be displayed as described in Table 502. If the “Y”
thermostat demand is removed, the counter that keeps track of the three pressure switch trips and the 120 minute period will be
reset. The Low pressure switch is ignored the rst 90 seconds after the compressor is energized. The Low pressure switch is ignored
if the “Y” thermostat demand is removed.
High Pressure Switch Operation (Heating)
Normally Closed. Open At 675 Psig And Close At 475 Psig.
If the High Pressure switch opens during heating operation, the compressor contactor will be de-energized and the ASCD will be
reset. During the period with a High pressure switch open, the “High Pressure Switch Open” fault condition will be displayed as
described in Table 502. If three High Pressure Switch faults happen within a 90 minute period and within the same call for heating,
the control will lockout the compressor and display the “High Pressure Switch Lockout” fault condition will be displayed as described
in Table 502. If the “Y” thermostat demand is removed, the counter that keeps track of the three pressure switch trips and the 90
minute period will be reset. The High pressure switch is ignored if the “Y” thermostat demand is removed.
OPERATION
Sequence of Operation
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