830841-BIM-D-0512
Johnson Controls Unitary Products
25
24 Volts AC is sent out of the “W1OUT” terminal of the DCB to
the “W1” terminal of the CFMCB and to the “W1” terminal on the
Spark Ignition Control Board (EMCB).
The induced draft motor (DM) is energized in high speed for
pre-purge of the heat exchanger. The control board continues
the pre-purge cycle for approximately 15 seconds and then
initiates an ignition trial period.
During the ignition trial period, the control board energizes the
pilot gas valve (P) and spark ignition for up to an 85 second trial
period.
When the Flame Sensor senses pilot flame (minimum of 0.2
microamperes), the pilot valve remains energized and spark
ignition is de-energized.
The EMCB control board waits approximately 2 seconds for
flame stabilization prior to energizing the main gas valve.
The EMCB will send 24 Volts AC to the “M” and “HI” terminals
of the gas valve operating the gas heat section at full fire for
approximately 60 seconds.
The EMCB de-energizes “H-IND” and provides 120 Volts AC
out of the “IND” terminal reducing the DM to low speed. Control
voltage is also removed from “HI” at the gas valve reducing gas
heat to low fire operation tempering the air provided to the
conditioned space.
30 seconds after a call for defrost, the reversing valve is
energized, the “ODF” contacts on the DCB are opened de-
energizing the outdoor fan motor and the compressor operates
at full capacity during defrost.
During defrost if the discharge pressure raises to 360psig, the
Furnace Control Pressure Switch (FCS) will close sending 24
Volts AC to the defrost relay coil (DR) de-energizing the gas
heat section. The DM would continue operating until the post
purge cycle timer expires.
When the discharge pressure drops back to 300psig, the DR
coil is de-energized and the gas heat section is available on the
next defrost or heating cycle.
Defrost Termination
Defrost is terminated when either the liquid line sensor reaches
65°F, or the maximum defrost time of 8 minutes has been
reached.
Note: The defrost termination temperature and time are
dependent on the selected defrost curve.
When the liquid line sensor or the maximum defrost timer has
reached the termination point:
Control voltage is removed from the “W1 OUT” terminal, de-
energizing the gas heat section. Control voltage is also
removed from the “RV” and “RVG” terminals de-energizing the
reversing valve. The “ODF” contacts on the DCB re-close
energizing the outdoor fan motor. Mechanical heating operation
resumes.
Emergency Heat Call
When the thermostat is set to emergency heat on the
Residential Dual Fuel Package Units, 24 Volts AC is provided to
the “W1” terminal on the Spark Ignition Control Board (EMCB).
The EMCB will send 120 Volts AC out of the “H-IND” terminals
energizing the DM in high speed for pre-purge of the heat
exchanger. The control board continues the pre-purge cycle for
approximately 15 seconds and then initiates an ignition trial
period.
The control board energizes the pilot terminal “P” on the gas
valve and spark ignition for up to an 85 seconds. When the
Flame Sensor senses pilot flame (minimum of 0.2
microamperes), the pilot valve remains energized and spark
ignition is de-energized.
The EMCB control board provides a 2 second flame
stabilization period prior to energizing the main gas valve. The
EMCB provides 24 Volts AC to the “M” and “HI” terminals of the
gas valve, operating the gas heat section at full fire for
approximately 60 seconds.
The EMCB then de-energizes “H-IND” at the DM and provides
120 Volts AC out of the “IND” terminal reducing the DM to low
speed. Control voltage is also removed from “HI” at the gas
valve reducing gas heat operation to low fire operation.
After operating at low gas heat for 15 minutes, the DCB will
provide 24 Volts AC to the “W2” terminal on the EMCB
energizing the gas valve at high fire. The EMCB will also send
120 Volts AC out of the “H-IND” terminal and remove 120 Volts
AC from the “IND” terminal energizing the DM at high speed.
The unit will continue to operate at full capacity (Gas Heat) until
the thermostat is satisfied. When the thermostat is satisfied, the
gas heat section is de-energized and the DM will operate for a
30 second post purge cycle. At the same time the blower will
operate until the on board Blower Off Delay selection of 60, 90,
120, or 180 seconds expires.
Outdoor Ambient Temperature is Between the Balance
Point and Low Temperature Cutout
First Stage Mechanical Heat Call –
“Y1” and “G” from the
thermostat:
Same as when Outdoor Ambient Temperature is above
Balance Point as previously discussed.
Second Stage Mechanical Heat Call
–
“Y1”, “Y2” and “G”
from the thermostat:
Same as when Outdoor Ambient Temperature is above
Balance Point as previously discussed.
Defrost –
Same as when Outdoor Ambient Temperature is above
Balance Point as previously discussed.
