035-17477-002 Rev. D (1202)
26
Unitary Products Group
Auxiliary Limit Controls:
Downflow/horizontal units have a
single limit switch mounted on the blower assembly. This is a
manual reset control and gives high temperature protection in
the event of a blower motor failure.
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 fac-
tory 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 and come
up to speed. Shortly after venter start-up, the hot
surface igniter will glow for about 17 seconds.
b.
After this warm up, the ignition module will energize
(open) the main gas valve 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 startup
due to residual air in the gas line or until gas manifold pres-
sure 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.
FIGURE 36 :
Pressure Switch Tubing Routing
Be sure proper ventilation is available to dilute and
carry away any vented gas.
UPFLOW
1LP
DOWNFLOW / HORIZONTAL
Perform the following procedures only after the
condensate trap has been properly piped to a
drain connection using the procedure in this
instruction.
DO NOT omit this test! Never use a flame to check
for gas leaks.
