4.8 VARIATIONS
4.9 TERMINATIONS
H21.3.2
2. When the 15 second pre-purge time has elapsed, the control energizes the HSI output for a 5 second
warm-up period (10 seconds on retries). The control energizes the low main gas valve. 4 seconds after the
gas is energized, the control de-energizes the HSI output and leaves the gas energized another 1 second
for fl ame proving. If fl ame is present at the end of trial for ignition time, the control leaves the gas valve
energized, exhauster on high speed, and begins heat blower on delay. The control always ignites on high
exhauster/low gas and ignores second stage call for heat until low fi re is established for 15 seconds.
3. Blower on delay time begins when the gas valve is energized. The control provides the ECM
(Electronically Commutated Motor) low heat speed signal when fl ame is proven, and starts a 30 second
blower delay before full capacity blower level.
4. When there is a demand for 2nd stage heat from thermostat W2 or automatic staging, the control changes
the exhauster from low to high speed. When high pressure switch closes, the control changes indoor
blower speed from Low heat to High heat and energizes high gas output. If the high pressure switch is
open the Green LED will fl ash. If the high pressure switch is closed the Green LED will be on. High gas
valve drops out while High pressure switch is open because it is directly in series with the high pressure
switch.
5. When the thermostat W2 call ends and W1 remains (two stage thermostat), the control de-energizes the
high gas output and immediately changes exhauster speed from high to low. With the thermostat heating
contacts open (single stage thermostat), the fl ames extinguish immediately and the exhauster blower
stops after a 5 second post purge time.
6. Blower off delay is handled by the ECM (Electronically Commutated Motor). The control de-energizes the
ECM heat signal when the gas valve de-energizes, and starts a programmed delay period.
IN THE EVENT OF FLAME FAILURE:
If fl ame is lost, the control de-energizes the gas valve within 2 seconds, switches the exhauster motor to
high speed (if not already on high), and begins timing the inter-purge delay. The indoor blower motor will be
energized and/or remain energized on heat speed for the programmed delay off time. When the inter-purge
delay is over, the control will re-cycle up to 5 fl ame losses (4 re-cycles) within a single call for heat before
going into lockout. The control fl ashes “8” on the Red LED if lockout is due to too many fl ame dropouts (1 hour
lockout).
H27.7
If your system includes air conditioning, your thermostat will likely have two switches. The fi rst switch is the
system switch. The switch settings usually include HEAT, COOL, and OFF. Some thermostats have system
switches which include HEAT, COOL, AUTO, and OFF. The system switch must be in the HEAT or AUTO
position for the furnace to run.
The second switch is the fan switch. It usually has settings of ON and AUTO. The fan switch may be in either
position when using the furnace. If the fan switch is set to ON, the main blower will run continuously.
H27.8
The combustion air and exhaust terminals should be inspected occasionally to ensure that they are free of
obstructions and debris. If screens were used in either terminal, ensure that they are free of debris, corrosion,
or anything preventing the free fl ow of air.
W415-1243 / E / 11.27.17
UM
72
Summary of Contents for ULTIMATE 9700 Series
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