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915SB: Installation, Start-up, Operating and Service and Maintenance Instructions
WINTERIZATION
Since the furnace uses a condensing heat exchanger, some water will
accumulate in the unit as a result of the heat transfer process. Therefore,
once it has been operated, it cannot be turned off and left off for an
extended period of time when temperatures will reach 32_F (0_C) or
lower unless winterized. Follow these procedures to winterize your
furnace:
1. Obtain propylene glycol (RV/swimming pool antifreeze or
equivalent).
2. Turn off gas and electrical supplies to your furnace.
3. Remove furnace control door.
4. Remove the top unused rubber plug from the port on the collector
box opposite the condensate trap. See
5. Connect a field supplied 3/8-in. (9.5-mm) ID tube to the open port
on the collector box.
6. Insert a field supplied funnel into the tube.
7. Pour one quart (liter) of anti-freeze solution into the funnel/tube.
Antifreeze should run through the inducer housing, overfill
condensate trap and flow to an open drain.
WARNING
!
ELECTRICAL SHOCK, FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal injury or death,
or property damage.
Before installing, modifying, or servicing system, main electrical
disconnect switch must be in the OFF position and install a lockout tag.
There may be more than one disconnect switch. Lock out and tag
switch with a suitable warning label. Verify proper operation after
servicing. Always reinstall access doors after completing service and
maintenance.
WARNING
!
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal injury, death,
and/or property damage.
Never purge a gas line into a combustion chamber. Never test for gas
leaks with an open flame. Use a commercially available soap solution
made specifically for the detection of leaks to check all connections. A
fire or explosion may result causing property damage, personal injury
or loss of life.
CAUTION
!
UNIT AND PROPERTY DAMAGE HAZARD
Failure to follow this caution may result in unit component or property
damage.
If the furnace is installed in an unconditioned space where the ambient
temperatures may be 32_ F (0_ C) or lower, freeze protection measures
must be taken to prevent minor property or product damage.
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
Fig.
60.
61
CAUTION
!
UNIT COMPONENT DAMAGE HAZARD
Failure to follow this caution may result in damage to the furnace and
other property damage.
Do not use ethylene glycol (automotive antifreeze coolant or
equivalent). Failure of plastic components may occur.
8. Replace the rubber plug in the port on the collector box.
9. Remove the middle unused rubber plug from the port on the
collector box opposite the condensate trap. See
10. Repeat Steps 5 through 8.
11. If a condensate pump is used, check with pump manufacturer to
verify pump is safe for use with antifreeze used. Allow pump to
start and pump anti-freeze to open drain.
12. Replace main door.
13. When furnace is re-started, flush condensate pump with clear water
to check for proper operation before re-starting furnace.
14. Propylene glycol need not be removed before re-starting furnace.
SEQUENCE OF OPERATION
NOTE: Furnace control must be grounded for proper operation or
control will lock out. Control is grounded through green/yellow wire
routed to gas valve and manifold bracket screw. Using the schematic
diagram in
Fig.
73, follow the sequence of operation through the
different modes. Read and follow the wiring diagram very carefully.
NOTE: If a power interruption occurs during a call for heat (W), the
control will start a 90-sec blower-only ON period two sec after power is
restored, if the thermostat is still calling for gas heating. The Amber
LED light will flash code 12 during the 90-sec period, after which the
LED will be ON continuous, as long as no faults are detected. After the
90-sec period, the furnace will respond to the thermostat normally.
The blower door must be installed for power to be conducted through the
blower door interlock switch ILK to the furnace control CPU,
transformer TRAN, inducer motor IDM, blower motor BLWM,
hot-surface igniter HSI, and gas valve GV.
1. Heating
See
Fig. 38
and
Fig. 39
for thermostat connections.
The wall thermostat "calls for heat," closing the R-to-W circuit.
The furnace control performs a self-check, verifies the pressure
switch contacts LPS and HPS are open, and starts the inducer motor
IDM.
a. Inducer Prepurge Period- As the inducer motor IDM comes up
to speed, the collector box pressure switch contacts LPS close to
begin a 15-sec prepurge period. The inducer housing pressure
switch contacts HPS are ignored until one minute after the gas
valve closes.
b. Igniter Warm-Up- At the end of the prepurge period, the
Hot-Surface igniter HSI is energized for a 17-sec igniter
warm-up period.
c. Trial-for-Ignition Sequence- When the igniter warm-up period
is completed, the main gas valve relay contacts GVR close to
energize the gas valve GV, the gas valve opens, and 24 vac power
is supplied for a field-installed humidifier at the HUM terminal.
The gas valve GV permits gas flow to the burners where it is
ignited by the HSI. Five sec after the GVR closes, a 2-sec flame
proving period begins. The HSI igniter will remain energized
until the flame is sensed or until the 2-sec flame proving period
begins.
d. Flame-Proving- When the burner flame is proved at the
flame-proving sensor electrode FSE, the furnace control CPU
begins the blower-ON delay period and continues to hold the gas
Fig.
60.
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