19
in the “HEAT” or “AUTO” position and the fan switch
in the “AUTO” position, the thermostat will close the
circuit between unit terminals R and W (R-W) when the
temperature falls below the thermostat setting.
2. D1 on IIC energizes relay VMR.
3. Relay VMR energizes the vent motor.
4. Operation of the vent motor closes the pressure switch
PS located in the burner compartment. the control then
initiates a 15-second pre-purge time delay. During this
period, the vent motor will clear the combustion chamber
of any residual gas.
5. After the pre-purge period, the ignition control energizes
the Wl-C gas valve and simultaneously initiates a “three
(3)-try” spark ignition sequence.
6. When the burners are ignited, a minimum four (4) micro-
amp DC current will flow through the flame between the
sensor electrode and the grounded burner.
7. When the controller proves that the flame has been
established, it will keep the gas valve energized and
discontinue the ignition spark. First stage manifold pressure
will be approximately 2.0” w.c. for natural gas and 7.0” w.c.
for propane (LP).
8. If the control is unable to ignite the burners after its initial
attempt, it will initiate another purge and spark sequence.
A third purge and spark sequence will be initiated if the
second attempt is unsuccessful. If the third attempt is
unsuccessful, the controller will close the gas valve and
lock itself out. It may be reset by momentarily interrupting
power. This may be accomplished by briefly lowering the
room thermostat set-point below room temperature, or
by shutting off the main power to the unit. (See TP-105 for
more details.)
9. Integrated ignition control will close its normally open
contacts after a delay of approximately 30 seconds. This
action energizes contactor BC and starts the supply fan
motor. Operation of the supply fan circulates air across the
heat exchanger and delivers heated air to the conditioned
space.
10. When the space temperature rises, the thermostat will
open R-W. Opening R-W will cause the gas valve to close,
and the furnace to shut down.
11. The furnace has three high temperature limit controls,
which can shut down the burner. They do not shut down
the vent motor.
Unit Shutdown
1. Set the thermostat to lowest setting.
2. Turn off the electrical power supply to the unit.
3. Remove the heat exchanger door on the side of the unit
by removing screws.
4. Move the gas control valve switch to the OFF position. Do
not force.
5. Close manual gas shut off valve external to the unit.
6. Replace the heat exchanger door on the unit.
7. If cooling and/or air circulation will be desired, turn ON
the electrical power.
Automatic Reset High Limit Control (LS)
Located in the burner compartment on the heat exchanger, its
sensing element projects through the blower section bulkhead and
senses the temperature at the rear of the furnace. It will cycle the
furnace off if the temperature exceeds 100°F plus maximum rise.
Auxiliary Reset High Limit Control (ALS)
Located in the blower compartment on the blower housing, it
senses air temperature within the blower compartment and pro-
tects the filters from excessive temperature. It will shut down the
furnace if it senses excessive temperatures.
Elevated temperatures at the control are normally caused by blow-
er failure. The reason for the opening should be determined and
repaired prior to resetting.
Manual Reset Flame Rollout Control (RS)
Located in the burner compartment at the top of the burner
assembly, it senses high temperature that could occur if the heat
exchanger tubes were plugged and the flame was rolling out instead
of entering the tubes. It has a manual push-button reset that cannot
be actuated until the limit control has cooled.
The reason for elevated temperatures at the control should be de-
termined and repaired prior to resetting this manual reset control.
T
O
AVOID
PROPERTY
DAMAGE
,
PERSONAL
INJURY
OR
DEATH
DUE
TO
FIRE
OR
EXPLOSION
,
A
QUALIFIED
SERVICER
MUST
INVESTIGATE
THE
REASON
FOR
THE
ROLLOUT
PROTECTION
DEVICE
TO
OPEN
BEFORE
MANUALLY
RESETTING
THE
ROLLOUT
PROTECTION
DEVICE
.
WARNING
Refrigeration System
The unit is equipped with a thermal expansion valve as a meter-
ing device.
Ensure the hold-down bolts on the compressor are secure and have
not vibrated loose during shipment. Check that vibration grommets
have been installed. Visually check all piping for damage and leaks;
repair if necessary. The entire system has been factory charged and
tested, making it unnecessary to field charge. Factory charges are
shown on the unit’s nameplate. To confirm charge levels or, if a
leak occurs and charge needs to be added to the system, it is rec-
ommended to evacuate the system and recharge refrigerant to unit
nameplate specifications. This unit has been rated in the cooling
mode at the AHRI rated conditions of: Indoor (80°db / 67°wb) and
outdoor (95°db). While operating at this condition, the subcooling
should range from 12° to 15° F for each refrigeration circuit, for 15
and 20 ton models. Subcooling for 25 ton models should be from
16° to 19° F for circuit 1, and from 12° to 15° F for circuit 2.
