8
OPERATION
SYSTEM CONTROLLER - HEAT PUMP
The System Controller will initially run in the mode requested by
the first calling zone thermostat.
Cool mode
- When running in the cool mode, the System
Controller energizes the compressor(s), indoor blower and the
reversing valve (O made to R) if the reversing valve selection
jumper is in the O position. This is indicated by the correspond-
ing Y, G and O/B (if jumper in O position) LEDs illuminating.
Dampers for the zones not calling for cool are powered closed
and the dampers for the zones calling for cool are left open.
This is indicated by the DPR LEDs. If the DPR LED is illuminated
on the damper terminal strip and the damper terminal board,
the corresponding damper is closed. The system will continue
to run in the cool mode until all calls are satisfied or changeover
occurs. When all calls are satisfied or prior to changeover, the
system will go into a purge mode.
Heat mode
- When running in the heat mode, the System
Controller energizes the compressor(s), indoor blower and the
reversing valve if the reversing valve selection jumper is in the B
position. This is indicated by the corresponding Y, G and O/B (if
jumper in B position) LEDs illuminating. Dampers for the zones
not calling for heat are powered closed and the dampers for the
zones calling for heat are left open. This is indicated by the DPR
LEDs. If the DPR LED is illuminated on the damper terminal strip
and the damper terminal board, the corresponding damper is
closed. After running in heat mode for 8 minutes, the System
Controller will energize the auxiliary heat if the coil leaving air
temperature drops below 90° and will de-energize when the
coil leaving air temperature rises above 100°. The W2 LED is on
when the auxiliary heat is energized. The system will continue to
run in the heat mode until all calls are satisfied or changeover
occurs. When all calls are satisfied or prior to changeover, the
system will go into a purge mode.
Changeover
-
While the system is operating in one mode,
and the System Controller recives a call for the opposite mode,
the System Controller will continue to run in the current mode
until the changeover TIME limit has been reached, or all current
calls have been satisfied. Then the System Controller will go into
a purge mode for 4 minutes, then changeover to the new
mode.
Purge mode
- Purge mode is initiated after the last calling
zone is satisfied, or when the controller goes into a forced
changeover. All HVAC output LEDs on the controller go off
during this cycle. When the last calling zone thermostat satisfies,
the Digitract controller goes into a 4 minute purge cycle. During
this time delay all outputs to the HVAC system and dampers are
terminated. All dampers go to a full open position and the
HVAC system fan delay runs the blower for a time. This time
delay with no control outputs allows the supply duct to return to
ambient temperature before the next call is initiated.
When the controller goes into a force mode changeover, and
the initial call drops out to the purge cycle, the HVAC outputs
are terminated, and the initial zone damper remains open for a
4 minute delay with the other dampers closing. The HVAC system
fan control allows the blower to run for a time, and the initial
calling zone supply duct returns to ambient temperature.
Auxiliary heat
- 8 minutes after the System Controller has
run in heat mode, if the coil leaving air temperature is below
90°, the auxiliary heat is energized and the W2 LED illuminates.
When the coil leaving air temperature rises above 100°, the
auxiliary heat is de-energized and the W2 LED cycles off.
Ventilation
- When no zones are calling, all zone dampers
are open. During this time, if any thermostat has the fan switch
ON then the indoor blower is energized (G made to R) and G
LED is on. This provides ventilation to all zones.
Emergency heat
- Emergency Mode is selected from STAT
1 position only. To make an emergency heat call, STAT 1 must
be in the emergency heat mode and make a heat call. When
STAT 1 places the call for heat, all thermostats will then be able
to place a call for emergency heat independently. Compres-
sors will be locked out of operation until STAT 1 places a cool
or heat call. When a call for emergency heat is placed the
blower and electric strip heat will energize. Zones that are not
calling for heat will close their dampers; those that are calling
will remain open.
Fossil Fuel Operation
- The DT4U provides a selectable
integrated Fossil Fuel operation. Applying this controller to
Fossil Fuel systems eliminates the need for a “Fossil Fuel Kit”,
additional capacity control, auxiliary relays and complicated
control wiring. The controller offers balance point control
when the optional FOAS outdoor air sensor is used. This en-
ables the heat pump compressor to be locked out and the
furnace to be energized on a call for heat, when the outdoor
temperature is below the BP setpoint on the DT4U controller.
When the FOAS is not used, the controller will stage up to the
furnace based on time and temperature.
By placing the controller jumper in the FF position the control-
ler is configured for Fossil Fuel operation. When there is no
Outside Air Sensor applied, a call for heat from any zone ener-
gizes Y1 compressor output and G blower output ( “B” mode
energizes rev valve also). With the factory POT settings: LO 45°
and HI 120°, the controller will stage up from Y1 to Y2 after
four minutes, if the supply air temperature is below 95°. After
8 minutes run time if the supply air temperature is 90° or
below, W2 LED will illuminate energizing the furnace; Y1 and
Y2 will drop out leaving the fan circuit energized. When the
controller energizes W2 for the furnace, the capacity control
automatically implements a fixed cutout temperature of
approximately 135°. When this temperature is exceeded, W2
drops out and the system goes into 4 minute purge cycle to
reduce supply air temperature.
When using the optional FOAS Outdoor Air Sensor, the
Balance Point “BP” POT should be checked and adjusted as
required; factory settings is 33°. On call for heat, if the OA
temperature is above the BP setting, Y1 will be energized on
the Heat Pump. When the OA is below the BP, call for heat will
energize W2 gas furnace directly.
