Page 44
SEQUENCE OF OPERATION – SINGLE-STAGE COM-
PRESSOR
NOTE - The combustion air inducer is energized for 30
seconds at a Y1 call for cooling to clear warm humid air
out of the heat exchanger.
Cooling
1 - Internal thermostat wiring energizes terminal ”O” by
cooling mode selection, energizing reversing valve
L1.
2 - Cooling demand initiates at Y1 in the indoor
thermostat.
3 - 24VAC from Y1 energizes compressor contactor
K1.
4 - K1-1 closes energizing compressor B1 and outdoor
fan motor B4.
5 - Compressor B1 and outdoor fan B4 begin immediate
operation.
6 - 6- Evaporator blower B3 begins operation.
7 - When cool demand is satised, ”Y1” in the indoor
thermostat de-energizes K1 contactor. K1-1 opens
de-energizing compressor B1 and outdoor fan
B4. Evaporator blower B3 de-energizes after 90
seconds of time delay.
8 - Terminal ”O” is de-energized when internal
thermostat is out of cool mode, de-energizing
reversing valve L1.
First Stage Heat Pump
1 - Heating demand initiates at ”Y1” in the thermostat.
2 - 24VAC energizes compressor contactor K1.
3 - K1-1 closes energizing compressor B1 and outdoor
fan B4.
4 - Evaporator blower B3 energizes after 5 seconds.
5 - When heat demand is satised, Y1 in the indoor
thermostat de-energizes K1. K1-1 and K1-2 open
and deenergizes compressor B1 and outdoor fan
B4.
6 - Evaporator blower B3 de-energizes after 90
seconds.
Second Stage Auxiliary Heat
1 - Heating demand initiates at ”Y1” and ”W” in the
thermostat. ”W” can either be strip heat in a HP unit
or gas burners in a DF unit.
Emergency Heat
1 - Emergency heat is energized by the room thermostat
through ”W”.
Defrost Mode
1 - During heating operation when liquid line
temperature drops to 42F or lower defrost switch S6
closes.
2 - Defrost control CMC1 begins timing. If defrost
thermostat S6 remains closed at the end of 30, 60
or 90 minute period, defrost control energizes and
defrost begins
NOTE - On early defrost controls, the defrost timing jump-
er must be in the 90-minute defrost interval before testing
the defrost mode or the control will not enter defrost test
mode.
3 - During defrost CMC1 energizes the reversing valve
L1 and de-energizes the outdoor fan B4. If the
compressor delay jumper is set, the compressor
will turn o for 30 seconds while the reversing valve
shifts either in or out of defrost mode.
4 - Defrost continues for 10 minutes or until defrost
thermostat switch S6 opens (S6 will open when
liquid line temperature reaches 70°). When defrost
thermostat switch opens, defrost control CMC1
loses power and resets.
5 - When CMC1 resets, reversing valve L1 is de-
energized while outdoor fan B4 is energized.
Gas Heat
1 - Heating demand W1 initiates at the indoor
thermostat.
2 - Assuming all safety circuits are closed (with the
exception of the pressure-prove switch open), A3
energizes the combustion air inducer blower B6.
When the N.O. combustion air inducer pressure-
prove switch S18 closes, a pre-purge period of 30
seconds follows.
3 - Ignition control A3 begins spark and energizes gas
valve GV1.
4 - Gas valve GV1 opens. When ame is sensed,
spark stops.
5 - After 30 seconds, ignition control A3 energizes
circulating air blower B3.
6 - When heat demand is satised, the indoor
thermostat de-energizes control A3 which de-
energizes gas valve GV1 and combustion air
inducer blower B6. Circulating air blower B3 runs
for a designated period of 90 seconds.
SEQUENCE OF OPERATION – TWO-STAGE COM-
PRESSOR
The two−stage scroll compressor operates much like the
standard scroll compressor. The two−stage compressor
steps between low capacity and high capacity as required
to meet cooling demand. The steps occur when gas is
bypassed through a vent port in the rst suction pocket.
This bypassing of gas allows the compressor to operate
at low capacity if thermostat demand allows, creating a
more cost eective and ecient compressor. Full capacity
is achieved by blocking the vent port with a slider ring.
The slider ring (vent port cover) is controlled by a 24VDC
internal solenoid in the open position allowing low capaci-
ty. When energized the internal solenoid closes the slider
ring, blocking the vent port and bringing the compressor
to full capacity.
Stepping can occur during a single thermostat demand as
the motor runs continuously while the compressor steps
from low to full capacity.
To Next Page
Loading...
Need help?
General
