035-19624-001 Rev. A (0104)
18
Unitary Products Group
IGNITION SYSTEM SEQUENCE
1.
Turn the gas supply
ON
at external valve. See Figure 7.
2.
Turn the gas valve switch to the
ON
position. See Figure 26.
3.
Set the thermostat above the room temperature to initiate the call
for heat.
4.
The furnace ignition system will start as follows:
a.
The Integrated Ignition Control Board will do a self-diagnostic
test.
b.
It will check all limits and pressure switch(s).
c.
The draft inducer motor will start high speed.
d.
Pressure switch(s) will close
e.
The draft inducer motor will go to low speed.
f.
The hot surface igniter will warm up for 17 seconds.
g.
Gas valve will open low fire for 7 seconds.
h.
Flame rectifaction will prove flame.
i.
Blower motor low heat comes on in 30 seconds.
j.
Thermostat call for W2.
k.
The draft inducer motor will go to high speed.
l.
Pressure switch will close.
m.
Gas valve will open high fire.
n.
Blower motor high heat comes on in 30 seconds.
o.
Thermostat W2 ends, gas valve will go to low fire.
p.
The draft inducer motor will go to low speed.
q.
Blower motor goes to low heat in 30 seconds.
r.
Thermostat ends call for heat.
s.
Draft inducer motor does 15 seconds post purge.
t.
Blower continues for adjusted time delayed.
IMPORTANT:
Burner ignition may not be satisfactory on first startup
due to residual air in the gas line or until gas manifold pressure is
adjusted. The ignition control will make 3 attempts to light before lock-
ing out.
With furnace in operation, check all of the pipe joints, gas valve connec-
tions and manual valve connections for leakage using an approved gas
detector, a non-corrosive leak detection fluid, or other leak detection
methods. Take appropriate steps to stop any leak. If a leak persists,
replace the component.
The furnace and its equipment shutoff valve must be disconnected from
the gas supply piping system during any pressure testing of the system
where test pressures are in excess of 1/2 PSI (3.45 kPa).
CALCULATING THE FURNACE INPUT
(NATURAL GAS)
NOTE:
Front door of burner box must be secured when checking gas
input.
NOTE:
Burner orifices are sized to provide proper input rate using nat
ural gas with a heating value of 1050 BTU/Ft
3
. If the heating
value of your gas is significantly different, it may be necessary to
replace the orifices.
1.
Turn off all other gas appliances connected to the gas meter.
2.
At the gas meter, measure the time (with a stop watch) it takes to
use 2 cubic ft. (0.0566 m
3
.) of gas.
3.
Calculate the furnace input by using one of the following equa-
tions.
In the USA use the following formula to calculate the furnace input.
For natural gas
multiply the heat content of the gas BTU/SCF (or Default 1030 BTU/SCF, times 2 cubic ft. of gas measured at the gas meter, times
a barometric pressure and temperature correction factor of 0.960; times 3600, then divided by the time (In seconds) it took to measure 2 cubic ft. of
gas from the gas meter.
For propane (LP)
gas multiply the heat content of the gas BTU/SCF (or Default 2500 BTU/SCF, times 1 cubic ft. of gas measured at the gas meter,
times a barometric pressure and temperature correction factor of 0.960; times 3600, then divided by the time (In seconds) it took to measure 1 cubic
ft. of gas from the gas meter.
The formula for US input calculation using a cubic foot gas meter:
FIGURE 26:
Gas Valve
R
E
P
L
A
C
E
R
E
P
L
A
C
E
SCRE
W
SCRE
W
PM
C
HI
O
F
F
ON
INLET
OUTLET
WRENCH
BOSS
ON / OFF SWITCH
HI ADJUST
LO
ADJUST
LOW FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
HIGH FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
BTU/f
3
x 2 cu.ft. x 0.960 x 3600
=
BTUH/H
BTU/f
3
x 2 cu.ft. x 0.960 x 3600
=
BTUH/H
Seconds it took to measure the 2 cu.ft. of gas
Seconds it took to measure the 2 cu.ft. of gas
NATURAL GAS INPUT CALCULATION
PROPANE (LP) GAS INPUT CALCULATION
EXAMPLE:
EXAMPLE:
1030 x 2 x 0.960 x 3600
=
79,997.38
2500 x 1 x 0.960 x 3600
=
80,000.00
90.5
108
Natural Gas
Propane Gas
BTU/SCF 1030
BTU/SCF 2500
