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U U n n i i t t S S t t a a r r t t u u p p
3. As the comfort control calls for heat, the system
cycles as follows:
a. The combustion blower is energized.
b. The pressure switch is closed.
c. The gas valve opens and the ignitor lights the
burner.
d. Cycle the thermostat on and off a few times to
check out the control system and burner operation
characteristics.
4. With the burners operating, check the manifold
pressure with a manometer. Do not exceed
recommended pressures.
5. Adjust the unit to obtain an air temperature rise
within the range that is specified on the unit
nameplate.
N N o o t t e e : : For manifold pressures and orifice sizes for
gas with other BTU ratings, contact the local
gas utility. Manifold pressure should be 1.8
(low) to 3.5 (high) inches water column (+0.1).
Input must n n o o t t exceed the value shown on
the unit nameplate.
6. Set the heat anticipator of the comfort control to
equal the amperage draw of the gas valve,
approximately 0.7.
7. Set the comfort control at the desired temperature
setting and the unit will function automatically.
Starting the Unit in the Gas
Heating Mode
1. Check to make sure all grilles and registers are open
and all unit access doors are closed before start-up.
2. Purge the gas supply line of air by opening the
union ahead of the unit. When the odor of gas is
detected, retighten the union and wait five (5)
minutes before proceeding.
3. Set the comfort control to its lowest position and
the fan to AUTO or ON.
4. Open the main gas valve(s) and turn on the unit
power supply.
5. Reset the heating temperature of the comfort
control to the highest value above room
temperature. The combustion blower motor should
energize. The main burners should light within 20-
25 seconds. Initial start may be delayed somewhat
if the unit has not been purged and air is trapped in
the gas line.
N N o o t t e e : : Blue smoke produced by the heat exchanger
during the initial burner firing is caused by a
thin film of oil on the surface of the heat
exchanger. This oil will burn off quickly.
24
Sequence of Operation
G G e e n n e e r r a a l l
Operation of the system cooling (and optional heating)
cycles is controlled by the setting of the system switch
on the room thermostat. Once the system switch is
placed either in the "HEAT" or "COOL" position, unit
operation is automatic. A fan switch on the thermostat
also provides for continuous operation of the
evaporator fan when desired. The fan switch "ON"
position provides continuous operation while the
"AUTO" position provides operation during the
heating or cooling cycles.
H H e e a a t t i i n n g g C C y y c c l l e e
T T h h e e r r m m o o s s t t a a t t c c a a l l l l f f o o r r h h e e a a t t
(R) and (W) thermostat contacts close signaling the
control module (IGN) to run its self-check routine. After
the control has verified that the pressure switch (PS)
contacts are open, the limit switch (TCO) contacts are
closed, and the flame rollout (RO) switch is closed, the
induced draft blower (CFM) will be energized.
After the induced draft blower (CFM) has come up to
speed, the control will verify that the pressure switch
(PS) contacts are closed and run the induced draft
blower for a 20 second pre-purge. The gas valve (GV) is
energized to permit gas flow and the spark ignitor (IP)
is energized. The flame detector (FD) confirms that
ignition has been achieved within the 7 second trial
period.
As the flame detector confirms that ignition has been
achieved the delay to indoor fan on period begins
timing and after approximately 45 seconds, the indoor
blower motor (IDM) will be energized and will continue
to run during the heating cycle
C C a a l l l l f f o o r r 2 2 n n d d s s t t a a g g e e a a f f t t e e r r 1 1 s s t t s s t t a a g g e e : :
(R) and (W2) thermostat contacts close signaling a call
for second stage heat. The induced draft motor (CBM)
is energized on high speed and the gas valve on
second stage. After approximately 30 seconds the
control energizes the indoor blower on high speed.
2 2 n n d d s s t t a a g g e e s s a a t t i i s s f f i i e e d d , , 1 1 s s t t s s t t a a g g e e s s t t i i l l l l c c a a l l l l e e d d : :
(R) and (W2) opens, the induced draft blower is
reduced to low speed the gas valve is reduced to first
stage. After about 30 seconds the indoor blower motor
is reduced to low speed.
1 1 s s t t s s t t a a g g e e s s a a t t i i s s f f i i e e d d : :
(R) and (W1) opens, the gas valve (GV) will close. The
induced draft blower (CBM) will be de-energized after
approximately 5 seconds postpurge. The indoor blower
motor (IDM) will continue to run for the fan off period
(field selectable 60 or 90 seconds [by jumpers]), then
will be de-energized by the control module.
C C o o m m f f o o r r t t C C o o n n t t r r o o l l c c a a l l l l f f o o r r h h e e a a t t ( ( 1 1 - - s s t t a a g g e e C C o o m m f f o o r r t t
C C o o n n t t r r o o l l ) )
(R) and (W1/W2) (jumped) thermostat contacts close
18-EB27D1-13C-EN
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