Bryant PACKAGED HEAT PUMP 548J - Manual (Page 66)

66
SEQUENCE OF OPERATION
Cooling, unit without economizer
When thermostat calls for cooling, terminals G and Y1 are
energized. The indoor-fan contactor (IFC), reversing valve
solenoid (RVS) and compressor contactor are energized
and indoor-fan motor, compressor, and outdoor fan starts.
The outdoor fan motor runs continuously while unit is
cooling.
Heating, unit without economizer
Upon a request for heating from the space thermostat,
terminal W1 will be energized with 24V. The IFC,
outdoor-fan contactor (OFC), C1, and C2 will be
energized. The indoor fan, outdoor fans, and compressor
no. 1, and compressor no. 2 are energized and reversing
valves are deenergized and switch position.
If the space temperature continues to fall while W1 is
energized, W2 will be energized with 24V, and the heater
contactor(s) (HC) will be energized, which will energize
the electric heater(s).
When the space thermostat is satisfied, W2 will be
deenergized first, and the electric heater(s) will be
deenergized.
Upon a further rise in space temperature, W1 will be
deenergized.
Cooling, unit with EconoMi$er IV
When free cooling is not available, the compressors will
be controlled by the zone thermostat. When free cooling is
available, the outdoor-air damper is modulated by the
EconoMi$er IV control to provide a 50 to 55_F (10_ to
13_C) mixed-air temperature into the zone. As the
mixed-air temperature fluctuates above 55 or below 50_F
(13_ to 10_C), the dampers will be modulated (open or
close) to bring the mixed-air temperature back within
control.
If mechanical cooling is utilized with free cooling, the
outdoor-air damper will maintain its current position at
the time the compressor is started. If the increase in
cooling capacity causes the mixed-air temperature to drop
below 45_F (7_C), then the outdoor-air damper position
will be decreased to the minimum position. If the
mixed-air temperature continues to fall, the outdoor-air
damper will close. Control returns to normal once the
mixed-air temperature rises above 48_F (9_C).
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be
energized and deenergized.
If field-installed accessory CO
2
sensors are connected to
the EconoMi$er IV control, a demand controlled
ventilation strategy will begin to operate. As the CO
2
level in the zone increases above the CO
2
setpoint, the
minimum position of the damper will be increased
proportionally. As the CO
2
level decreases because of the
increase in fresh air, the outdoor-air damper will be
proportionally closed.
For EconoMi$er IV operation, there must be a thermostat
call for the fan (G). If the unit is occupied and the fan is
on, the damper will operate at minimum position.
Otherwise, the damper will be closed.
When the EconoMi$er IV control is in the occupied mode
and a call for cooling exists (Y1 on the thermostat), the
control will first check for indoor fan operation. If the fan
is not on, then cooling will not be activated. If the fan is
on, then the control will open the EconoMi$er IV damper
to the minimum position.
On the initial power to the EconoMi$er IV control, it will
take the damper up to 2 1 /
2
minutes before it begins to
position itself. Any change in damper position will take
up to 30 seconds to initiate. Damper movement from full
closed to full open (or vice versa) will take between 1 1 /
2
and 2 1 /
2
minutes.
If free cooling can be used as determined from the
appropriate changeover command (switch, dry bulb,
enthalpy curve, differential dry bulb, or differential
enthalpy), then the control will modulate the dampers
open to maintain the mixed-air temperature setpoint at
50_ to 55_F (10_ to 13_C).
If there is a further demand for cooling (cooling second
stage — Y2 is energized), then the control will bring on
compressor stage 1 to maintain the mixed-air temperature
setpoint. The EconoMi$er IV damper will be open at
maximum position. EconoMi$er IV operation is limited to
a single compressor.
Heating, unit with EconoMi$er
When the room temperature calls for heat through
terminal W1, the indoor (evaporator) fan contactor (IFC)
and heater contactor no. 1 (HC1) are energized and the
reversing valve(s) deenergize and switches position. On
units equipped for 2 stages of heat, when additional heat is
needed, heater contactor no. 2 is energized through W2.
The economizer damper moves to the minimum position.
When the thermostat is satisfied, the damper moves to the
fully closed position.
Defrost
When the temperature of the outdoor coil drops below
28_F (--2_C) as sensed by the defrost thermostat (DFT2)
and the defrost timer is at the end of a timed period
(adjustable at 30, 60, 90 or 120 minutes), reversing valve
solenoids (RVS1 and RVS2) are energized and the OFC is
deenergized. This switches the position of the reversing
valves and shuts off the outdoor fan. The electric heaters
(if installed) will be energized.
The unit continues to defrost until the coil temperature as
measured by DFT2 reaches 65_F (18_C), or the duration
of defrost cycle completes a 10-minute period.
During the Defrost mode, if circuit 1 defrosts first, RVS1
will oscillate between Heating and Cooling modes until
the Defrost mode is complete.
548J