035-17468-001 Rev. A (801)
Unitary Products Group
25
LIMIT CONTROL
There are high temperature limit control(s) located on the fur-
nace vestibule panel near the gas valve. These are automatic
reset controls and provide over temperature protection due to
reduced airflow, such as a dirty filter.
START-UP AND ADJUSTMENTS
The initial start-up of the furnace requires the following addi-
tional procedures:
1.
When the gas supply is initially connected to the furnace,
the gas piping may be full of air. In order to purge this air,
it is recommended that the ground union be loosened
until the odor of gas is detected. When gas is detected,
immediately retighten the union and check for leaks.
Allow five minutes for any gas to dissipate before con-
tinuing with the start-up procedure.
2.
The condensate trap must be filled with water before put-
ting the furnace into operation. The recommended pro-
cedure is as follows:
a.
Disconnect the condensate drain hose from the
induced draft blower discharge.
b.
Elevate this hose and fill with water using a funnel.
c.
Replace the condensate drain hose and clamps.
NOTE:
If this procedure is not followed, the unit may not
properly drain on initial start up.
3.
All electrical connections made in the field and in the
factory should be checked for proper tightness.
IGNITION SYSTEM SEQUENCE
1.
Turn the gas supply ON at external valve and main gas
valve.
2.
Set the thermostat above room temperature to call for
heat.
3.
System start-up will occur as follows:
a.
The induced draft blower motor will start at high
speed and wait for low pressure switch contacts to
close, then switch to low speed and the hot surface
ignitor will glow for approximately 17 seconds.
b.
The ignition module will energize (open) the main
gas valve on low fire for seven seconds.
c.
After flame is established, the supply air blower will
start in about 30 seconds.
NOTE:
Burner ignition may not be satisfactory on first start-
up 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 locking out.
4.
With furnace in operation, paint the pipe joints and valve
gasket lines with a rich soap and water solution. Bubbles
indicate a gas leak. Take appropriate steps to stop the
leak. If the leak persists, replace the component.
GAS VALVE OPERATION
The electronic switch is a two-position (ON-OFF) type. To
turn the valve ON, flip the switch to line up the word ON on
the switch housing, Refer to Figure 36.
Be sure proper ventilation is available to dilute and
carry away any vented gas.
Perform the following procedures only after the con-
densate trap has been properly piped to a drain con-
nection using the procedure in this instruction.
DO NOT omit this test! Never use a flame to check
for gas leaks.
FIGURE 36 :
Gas Valve (Top) Manual Control Knob
(Bottom) Regulator Adjustments
R
E
P
LA
CE
R
E
P
LA
CE
SCRE
W
SCRE
W
INLET
OUTLET
ON / OFF SWITCH
WRENCH
BOSS
LOW FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
HIGH FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
HI ADJUST
LO
ADJUST
PM
C
HI
O
F
F
ON
