18-BB42D1-1A-EN
19
Sequence of Operation
G
Geenneerraall
Operation of the unit heating and cooling cycles is
automatic when the system is set to H
HEEA
ATT or C
CO
OO
OLL
(the optional automatic changeover thermostat, when
set to A
AU
UTTO
O, automatically changes to heat or cool
with an appropriate room temperature change). The
fan can be set to O
ON
N, causing continuous evaporator
(indoor) fan operation or set to A
AU
UTTO
O causing fan
operation to coincide with heating or cooling run
cycles. Continuous fan mode during cooling operation
may not be appropriate in humid climates. If the indoor
air exceeds 60% relative humidity or simply feels
uncomfortably humid, it is recommended that the fan
only be used in the A
AU
UTTO
O mode. With the thermostat
set to O
ON
N current is supplied to the control transformer
(on 460v models the outdoor fan relay (ODF) is
energized through normally closed contacts on the
defrost control (DFC).
C
CO
OO
OLLIIN
NG
G M
MO
OD
DEE
TThheerrm
moossttaatt ccaallll ffoorr ccoooolliinngg ((22--ssttaaggee tthheerrm
moossttaatt))
C
Caallll ffoorr 11sstt ssttaaggee ccoooolliinngg oonnllyy::
With the room thermostat set to C
CO
OO
OLL and the fan set
to A
AU
UTTO
O, power is supplied from the room thermostat
"O" terminal to the unit switchover valve coil (SOV) and
the "O" terminal on the ECMC board. This energizes the
switch-over valve (SOV) placing it in the position for
cooling (it is in the position for heating when de-
energized). On a call for cooling, power is supplied to
the unit from the room thermostat (Y1) and (G)
terminal. (Y1) provides power to the compressor
contactor (CC), the defrost control (DFC) and the
electronically commutated motor control (ECMC). (G)
provides power to the (ECMC) for low speed (IDM)
indoor fan motor operation.
The energized compressor contactor (CC) completes
the circuit to the compressor for 1st stage (Low)
operation and the outdoor single speed fan motor
(ODM). The (G) signal energizes the (ECMC) for the
indoor fan motor (ECM) to operate on low speed. The
thermostat will continue to cycle the compressor and
fans to maintain the desired temperature.
C
Caallll ffoorr 22nndd ssttaaggee aafftteerr 11sstt ssttaaggee
On a call for 2nd stage cooling, power is supplied from
the room thermostat (Y2) terminal to the A/C rectifier
(ACR) and the (ECMC). This energizes the (ACR)
switching the compressor to 2nd stage (High)
operation. The (ECMC) is energized for indoor fan
motor (ECM) high speed fan operation. The room
thermostat will continue to cycle the system between
1st and 2nd stage to maintain the desired temperature.
H
HEEA
ATTIIN
NG
G M
MO
OD
DEE
TThheerrm
moossttaatt ccaallll ffoorr hheeaatt ((22--ssttaaggee tthheerrm
moossttaatt))
C
Caallll ffoorr 11sstt ssttaaggee hheeaattiinngg oonnllyy::
With the room thermostat set to H
HEEA
ATT and the fan set
to A
AU
UTTO
O, no power is supplied from the room
thermostat "O" terminal to the unit switchover valve
coil (SOV) and the "O" terminal on the ECMC board.
This leaves the switch-over valve (SOV) in the normal
position for heating and is the signal for the (ECMC) to
run at indoor fan speeds designed for heating. On a call
for heating, power is supplied to the unit from the
room thermostat (Y1) and (G) terminal. (Y1) provides
power to the compressor contactor (CC), the defrost
control (DFC) and the electronically commutated motor
control (ECMC). (G) provides power to the (ECMC) for
low speed (ECM) indoor fan motor operation.
The energized compressor contactor (CC) completes
the circuit to the compressor for 1st stage (Low)
operation and the outdoor single speed fan motor
(ODM). The indoor fan motor (ECM) will operate on low
speed. The room thermostat will continue to cycle the
compressor and fans to maintain the desired
temperature.
C
Caallll ffoorr 22nndd ssttaaggee aafftteerr 11sstt ssttaaggee
On a call for 2nd stage heating, power is supplied from
the room thermostat (Y2) terminal to the compressor
rectifier (ACR) and the (ECMC). This energizes the
(ACR) switching the compressor to 2nd stage (High)
operation. The (ECMC) is energized for indoor fan
motor (ECM) high speed fan operation. The room
thermostat will continue to cycle the system between
1st and 2nd stage to maintain the desired temperature.
S
Suupppplleem
meennttaarryy H
Heeaatt
The supplementary electric heat is brought on when
the indoor temperature drops below the thermostat
setting. The thermostat provides power from the "W"
terminal to the supplementary heater control circuit.
Note that the fan relay (F) must have been energized.
An outdoor thermostat may have been added to
disallow the second stage (if provided) of electric heat
above a selected outdoor temperature. If the outdoor
temperature falls below the setting on the outdoor
thermostat, this additional heater stage will come on.
When the outdoor air temperature rises, and the
outdoor T-stat setpoint is reached, the system will
revert back to first stage electric heating.
When the indoor ambient is satisfied, "W" contacts will
open and the unit will revert back to the compressor
only heating mode and then off. For emergency heat
(use of supplementary electric heat only), an
emergency (EMERG) heat switch is provided within the
thermostat. When placed in the emergency heat
position, it will disable the compressor, bypass the
outdoor thermostats, if provided, and engage the
supplementary electric heaters and indoor fan.
