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035-17405-000 Rev. B (0801)
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 joint union be loos-
ened 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
continuing with the start-up procedure.
2.
All electrical connections made in the field and in the fac-
tory should be checked for proper tightness.
IGNITION SYSTEM CHECKOUT/ADJUSTMENT
1.
Turn the gas supply ON at external manual shut-off
valve and main gas valve.
2.
Set the thermostat above the room temperature to call
for heat.
3.
System start-up will occur as follows:
a.
The venter 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 cycle, the ignition module will
energize (open) the main gas valve for seven sec-
onds.
c.
After flame is established, the supply air blower will
start within 30 seconds.
NOTE: Burner ignition may not be satisfactory on first start-
up due to residual air in gas line, or until gas pressure (mani-
fold) is adjusted. The control will make 3 attempts to light
before locking out.
4.
With the 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 leaks. If the leak persists, replace the compo-
nent.
CAUTION
DO NOT omit this test! NEVER use a flame to
check for gas leaks.
CHECKING GAS INPUT
1.
Turn off all other gas appliances connected to gas meter.
2.
With the furnace turned on, measure the time needed for
one revolution of the hand on the smallest dial on the
Unitary Products Group
FIGURE 14 : GAS VALVES
(Top) Whit-Rodgers 36E24
(Bottom) Honeywell VR8205
(approved for field replacement)
meter. A typical domestic gas meter usually has a 1/2 or
1 cubic foot test dial.
3.
Using the number of seconds for each revolution and the
size of the test dial increment, find the cubic feet of gas
consumed per hour. Refer to Table5 on page18.
NOTE: To find the Btuh input, multiply the number of cubic
feet of gas consumed per hour by the BTU content of the gas
in your particular locality. Contact your gas company for this
information, as it varies widely from city to city.
EXAMPLE:It is found by measurement that it takes 26 sec-
onds for the hand to turn on the 1 cubic foot dial to make a
revolution with only a 120,000 Btuh furnace running. Using
this information, locate 26 seconds in the first column of
Table5 .
Read across to the column headed 1 Cubic Foot where you
will see that 138 cubic feet of gas per hour are consumed by
the furnace at that rate. Multiply 138 by 850 (the BTU rating
of the gas obtained from the local gas company). The result
is 117,300 Btuh, which is close to the 120,000 Btuh rating of
the furnace.
17
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