32
18-GE20D1-1E-EN
Sequence of Operation
NNoottee:: The seven segment LED readout is based on
thermostat input.
NNoottee:: Some units will show demand airflow while
others will show calculated airflow. Calculated
airflow will gradually ramp up and may take ~1-2
minutes to stabilize.
EEAACC aanndd HHUUMM TTiimmiinngg
• EAC relay closes approximately 2 seconds after the
blower starts.
• EAC relay opens when the blower motor stops.
• HUM relay closes on any heating call (HP)
approximately 1 second after the blower motor
starts.
• HUM relay opens when any heating call (HP) is
removed.
SSiinnggllee SSttaaggee CCoooolliinngg
1. R-Y1-G contacts on the thermostat close sending
24VAC to the Y1 and G low voltage terminals on the
IMBC. Technician should read 24VAC between Y1-
B/C and between G-B/C.
NNoottee:: Factory supplied Y1-O jumper must remain in
place for proper seven segment LED readout.
If removed, seven segment LED will read
“
HP1
”.
2. 24VAC is sent to the OD unit via thermostat wiring
energizing 1
st
stage compressor operation.
3. The indoor blower ramps to the 1
st
stage cooling
airflow. The seven segment LED for example will
alternately read:
CL1 = Cooling, Stage 1
ARF = Airflow
080 = 800 calculated cfm (value shown x 10)
4. When the temperature is lowered enough to satisfy
the thermostat setting, contacts R-Y1-G will open.
The OD unit shuts off and the indoor blower shuts
off, unless a blower off delay has been enabled in
the IMBC setup menu options. The seven segment
LED will read “IDL” = Idle, no thermostat demand.
TTwwoo SSttaaggee CCoooolliinngg
1. See sequence of operation for Single stage cooling
operation above (see steps 1-4).
2. R-Y2 contact on the thermostat closes sending
24VAC to Y2 low voltage terminal on the IMBC.
Technician should read 24VAC between Y2 and B/C.
3. 24VAC is sent to the OD unit via thermostat wiring.
4. The indoor airflow ramps to 2
nd
stage cooling
airflow. The seven segment LED for example will
read:
CL2 = Cooling, Stage 2
ARF = Airflow
160 = 1600 calculated cfm (value shown x 10)
5. When the temperature is lowered enough to satisfy
the thermostat setting, contacts R-Y1-Y2-G will
open.
6. The OD unit shuts off and the indoor blower shuts
off, unless a blower off delay has been enabled in
the IMBC setup menu options. The seven segment
LED will read “IDL” = Idle, no thermostat demand.
SSiinnggllee SSttaaggee HHeeaatt PPuummpp
1. R-Y1-G contacts on the thermostat close sending
24VAC to the Y1 and G low voltage terminals on the
IMBC. Technician should read 24VAC between Y1-
B/C and between G-B/C.
NNoottee:: Factory supplied Y1-O jumper must be
removed for proper seven segment LED
readout. If left in place, seven segment LED
will read “
CL1
”.
2. 24VAC is sent to the OD unit via thermostat wiring
energizing 1
st
stage compressor operation.
3. The indoor blower ramps to the 1
st
stage heat
pump airflow. The seven segment LED for example
will alternately read:
HP1 = Heat Pump heating, Stage 1
ARF = Airflow
080 = 800 calculated cfm (value shown x 10)
4. When the temperature is raised enough to satisfy
the thermostat setting, contacts R-Y1-G will open.
The OD unit shuts off and the indoor blower shuts
off, unless a blower off delay has been enabled in
the IMBC setup menu options. The seven segment
LED will read “IDL” = Idle, no thermostat demand.
TTwwoo SSttaaggee HHeeaatt PPuummpp
1. See sequence of operation for Single stage heat
pump operation above (see steps 1-4).
2. R-Y2 contact on the thermostat closes sending
24VAC to Y2 low voltage terminal on the IMBC.
Technician should read 24VAC between Y2 and B/C.
3. 24VAC is sent to the OD unit via thermostat wiring
energizing 2
nd
stage compressor operation.
4. The indoor blower ramps to the 2
nd
stage heat
pump airflow. The seven segment LED for example
will alternately read:
HP2 = Heat Pump heating, Stage 2
ARF = Airflow
160 = 1600 calculated cfm (value shown x 10)