Rheem 96MDV Series, Installation Instructions Manual

Page: 83 / 128

83
COMMUNICATING FURNACE CONTROL
START-UP AND SEQUENCE OF OPERATIONS
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This furnace is equipped with a direct ignition control.
Each time the room thermostat calls for heat, the ignitor
lights the main burners directly. See the lighting instruc-
tions on the furnace.
TO START THE FURNACE
1. Remove the burner compartment control access door.
2. IMPORTANT: Be sure that the manual gas control has
been in the “OFF” position for at least five minutes. Do
not attempt to manually light the main burners.
3. Turn off the furnace electrical power and set the room
thermostat to its lowest setting.
4. Turn the gas control to the “ON” position or move the
gas control lever to the “On” position.
5. Replace the burner compartment control access door.
6. Turn on the furnace electrical power.
7. Set the room thermostat to a point above room tem-
perature to light the main burners. The heat call
should be adequate to activate the high stage gas
heat – generally, the thermostat setpoint should be
more than 2°F above room temperature. Consult your
thermostat specs to be sure.
8. Operate high gas heat for a minimum period of 15
minutes and adjust input rate (See Section of this
book titled
Adjusting Input Rate ) and observe con-
densate system for leaks. Correct leaks and set rate,
shut down furnace and repeat until no leaks in con-
densate system can be detected.
9. Once high heat operation has been successfully veri-
fied and rate adjusted, the thermostat should be ad-
justed to set the heat call to low stage. This is
generally with the heating setpoint at about 1°F above
room temperature. Consult your thermostat specs to
be sure.
10. Operate low gas heat for a minimum period of 15 min-
utes and adjust input rate (page 88) and observe con-
densate system for leaks. Correct leaks and set rate,
shut down furnace and repeat until no leaks in con-
densate system can be detected.
TO SHUT DOWN THE FURNACE
1. Set the room thermostat to its lowest setting and wait
for furnace to shut down.
2. Remove the burner compartment control access
door.
3. Shut off the gas to the main burners by turning the
gas control to the “OFF” position.
SEQUENCE OF OPERATION
HONEYWELL CONTROLS Integrated Controls
with Direct Spark Ignition.
1. Each time the thermostat “W” (Heating) contacts close
(legacy) or a communicating heat call is transmitted to
the furnace control from a communicating thermostat,
the furnace control checks to make sure that both
pressure switches are open. This is true of a low or
high heat call as “W” is energized on either call. Next
the induced draft blower (inducer) begins a pre-purge
cycle at high stage.
2. The air proving negative pressure switches (both low
and high) close.
3. After the 30-second pre-purge, the gas valve opens
on high stage for an 8-second trial for ignition.
4. The spark igniter is energized to light the gas burners
and stays energized for the up to 7 seconds after
the gas valve opens.
5. Eight seconds after the gas valve opens the remote
flame sensor must prove flame ignition for one
second using the process of flame rectification. If the
burners don’t light, the system goes through another
ignition sequence. It does this
up to four times before
entering a 1-hour lockout.
6. Twenty seconds after flame is sensed, the gas valve
is set to the thermostat demand (low or high) (note if
thermostat demand is high, the gas valve is already at
high stage and will not switch) and the main blower
will be energized at either the low or high gas heat
stage depending on the thermostat demand.
7. When the thermostat “W” (legacy) or communicated
heat call ends, the gas valve closes, flame is extin-
guished, the induced draft blower stops after
a 10-
second post-purge, and the negative pressure
switch opens.
8. The main blower continues until timed off by the set-
ting on the integrated furnace control board.
Sequence if the system doesn’t light or doesn’t sense
flame:
1. Each time the thermostat “W” (Heating) contacts
close, the furnace control checks to make sure that
both pressure switches are open. This is true of a low
or high heat call as “W” is energized on either call.
Next the induced draft blower (inducer) begins a pre-
purge cycle at high stage.
2. After the 30-second pre-purge, the gas valve opens
on high stage for an 8-second trial for ignition.
!
WARNING
SHOULD OVERHEATING OCCUR OR THE GAS
SUPPLY FAIL TO SHUT OFF, CLOSE THE MANUAL
GAS VALVE FOR THE APPLIANCE BEFORE SHUT-
TING OFF THE ELECTRICAL SUPPLY. FAILURE TO
DO SO CAN CAUSE AN EXPLOSION OR FIRE RE-
SULTING IN PROPERTY DAMAGE, PERSONAL IN-
JURY OR DEATH.