935SA: Installation, Start-up, Operating and Service Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
56
11. Check furnace operation through two complete heat operating
cycles.
12. Check for gas leaks.
13. Replace main furnace door.
Secondary Heat Exchangers
The condensing side (inside) of the secondary heat exchanger CANNOT
be serviced or inspected without complete removal of the heat exchanger
assembly. Detailed information on heat exchanger removal can be
obtained from your Distributor.
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.
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.
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.
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.
Propylene glycol need not be removed before re-starting furnace.
SEQUENCE OF OPERATION
NOTE:
Furnace control must be grounded for proper operation of
furnace control and flame sensing electrode. Control is grounded
through green/yellow wire routed to gas valve and burner box screw.
Using the schematic diagram in
, 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-second blower-only ON period two seconds after
power is restored, if the thermostat is still calling for gas heating. The
LED light will flash
12
during the 90-second period, after which the
LED will
ON continuous
, as long as no faults are detected. After the
90-second blower-on period, the furnace will respond to the thermostat
normally.
NOTE:
If BTS happens to be open as well, the inducer will operate
during the 90s. If the BTS does not reset during this time, a permanent
lockout will result and power must be cycled to reset. Check BTS and
fault code
26
for more information.
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.
Sequence of Operation - Heating
1.
Call for Heat:
The wall thermostat “calls for heat”, closing the R
-
W circuit. The
furnace control performs a self-check, verifies the transducer reads
no pressure present, and starts the inducer motor IDM ramp to
prepurge
a.
Inducer Prepurge Period:
The furnace control CPU ramps up
the inducer motor IDM to prepurge pressure then the furnace
control CPU begins a 15-second prepurge period. If the
transducer fails to reach target pressure the inducer motor IDM
will remain running until target pressure is maintained.
b.
Igniter Warm-Up:
At the end of the prepurge period, the
Hot-Surface Igniter HSI is energized for a 17-second igniter
warm-up period. Inducer maintains pressure during igniter
warm-up or 5 minutes has elapsed. Retry after 15 minutes.
c.
Trial for Ignition:
When the igniter warm-up period is
completed the main gas valve relay contact GVR closes to
energize the gas valve solenoid GV. The gas valve solenoid GV
permits gas flow to the burners where it is ignited by the HSI.
Five seconds after the GVR closes, a 2-second flame proving
period begins. The HSI igniter will remain energized until the
flame is sensed or until the 2-second flame proving period
begins.
d.
Flame Proving:
When the burner flame is proved at the flame
sensor electrode FSE, the inducer motor IDM will increase speed
(after a short delay of 14 seconds on some modes) to a higher
RUN pressure. The control will maintain this pressure once
reached, and the furnace control CPU will begin the blower-ON
delay period while continuing to hold the gas valve GV open. If
the burner flame is not proved within the 2-second flame proving
period, the control CPU will open the gas valve relay GVR,
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.
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.
