1101790-UIM-C-0414
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Johnson Controls Unitary Products
“RVG” terminals on the DCB energizing the reversing valve for
cooling operation.
The compressor, reversing valve, outdoor fan motor and blower
motor are energized in first stage operation.
Second Stage Cooling Call –
“Y1”, “Y2”, “O”, and “G” from
the thermostat:
After a first stage call for cooling and any delays from the
thermostat, if a second stage call is initiated from the thermostat
at the “Y2” terminal:
24 Volts AC is sent from the thermostat to the “Y2” terminal of
the DCB, and is sent out of the “M2” terminal to Terminal Block
2 (TB2). This provides 24 Volts AC to the rectifier located on the
compressor. The rectifier converts the 24 Volts AC to DC
voltage, providing DC control voltage to a solenoid internal to
the compressor for full capacity operation.
At the same time the compressor is energized at full capacity,
24 Volts AC is provided at the outdoor fan motor for high speed
operation.
Exception: 2 ton dual fuel units operate the outdoor fan at high
speed anytime the compressor is operating.
When the outdoor unit is energized at full capacity, 24 Volts AC
is also sent out of the “Y2OUT” terminal on the DCB to the “Y/
Y2” terminal of the CFMCB, energizing the ECM Blower Motor
for second stage cooling airflow.
At this time the compressor, reversing valve, outdoor fan motor,
and indoor blower are in second stage cooling operation.
Pressure Switch Proving
The control board energizes the induced draft motor (High speed
for 2 stage model) and waits for the low pressure switch to close.
When the low pressure switch closes, the control begins Pre-
purge period. If the call for heat is lost, the control de-energizes
the inducer without post-purge and returns to standby.
If the low pressure switch does not close within 10 seconds of
inducer energizing, the control board flashes “2” on the LED. If
the pressure switch does not close within 5 minutes of inducer
energizing, the control shuts off the inducer for 30 seconds,
then energizes the inducer for another 5 minute try to close the
pressure switch. This cycle continues indefinitely until either the
pressure switch is proved closed, or the call for heat ends.
Heating when the Outdoor Ambient Temperature is Greater
than the Balance Point
First Stage Mechanical Heat Call –
“Y1” and “G” from the
thermostat:
On a first stage mechanical heating call, the thermostat sends
24 Volts AC out of the “Y1” terminal to the CFM Selector Board
(CFMCB). When the CFMCB receives 24 Volts AC at “Y1”,
control voltage is sent to the “Y1” terminal of the YorkGuard VI
Defrost Control Board (DCB) energizing the “M1” contactor coil.
When the contactor coil is energized, the compressor operates
in first stage mechanical heating.
At the same time the compressor is energized, the “ODF”
contacts on the DCB close and provide control voltage to the
outdoor ECM 142R fan motor energizing the motor in first stage
operation.
Exception: The 2 ton dual fuel units operate the outdoor fan at
high speed anytime the compressor is operating.
When the compressor is energized, the CFMCB energizes the
ECM Blower Motor in first stage mechanical heating fan speed.
At this time the compressor, outdoor fan motor and blower are
operating in first stage heating mode.
Second Stage Mechanical Heat Call –
“Y1”, “Y2” and “G”
from the thermostat:
After a first stage call for mechanical heat and any delays from
the thermostat, when a second stage call is initiated from the
thermostat at the “Y2” terminal:
24 Volts AC is sent from the thermostat to the “Y2” terminal of
the DCB and is sent out of the “M2” terminal to Terminal Block 2
(TB2).
This provides 24 Volts AC to the rectifier located on the
compressor. The rectifier converts the 24 Volts AC to DC
voltage and energizes the compressor at full capacity
operation. At the same time the compressor is energized at full
capacity, 24 Volts AC is provided at the outdoor fan motor for
high speed operation (second stage).
When the outdoor unit is energized at full capacity, 24 Volts AC
is also sent from the “Y2OUT” terminal on the DCB to the “Y/
Y2” terminal of the CFMCB. This provides control voltage to the
ECM Blower Motor for second stage mechanical heating
airflow.
At this time the compressor, outdoor fan motor, and indoor
blower are operating in second stage mechanical heating
mode.
Third Stage Heat Call
If the thermostat initiates a third stage heat call when the
outdoor ambient temperature is above the selected Balance
Point on the DCB, gas heating operation is not allowed. The
only exception to this would be if there is a continuous heating
call for 4 hours at which time the gas heat section would be
energized and mechanical heating would be terminated 30
seconds after the initiation of gas heating. (4 Hour Pipe Freeze
Protection)
Defrost
When the liquid line and ambient sensors indicate that defrost is
required, the supplemental gas heating section is energized for
30 seconds before defrost is initiated. This allows the heat
exchanger time to begin warming up prior to reversing
refrigerant flow.
