035-17438-001 Rev. A (901)
14
Unitary Products Group
STARTUP AND ADJUSTMENTS
The initial startup 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 startup 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 valve and main gas
valve.
2.
Set the thermostat above room temperature to call for
heat.
3.
System startup will occur as follows:
a.
The ventor motor will start and operate on low
speed. Shortly after ventor startup, the hot surface
ignitor will glow for about 17 seconds.
b.
After this warm-up cycle, 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 within 30 seconds.
NOTE:
Burner ignition may not be satisfactory on first star-
tup due to residual air in gas line, or until gas pressure (mani-
fold) is adjusted.
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.
Gas Valve Operation
The manual switch is a two-position (ON-OFF) type. To turn
the valve on, move switch to the “ON” position. Refer to Fig-
ure 11 on page 15.
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
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 from Table 4 on page 15.
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. Contract 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.
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.
If the actual input is not within
+
2% of the furnace rating, with
allowance being made for the permissible range of the regu-
lator setting (0.3 inches W.C.), replace the orifice spuds with
spuds of the proper size.
ADJUSTMENT OF MANIFOLD GAS PRESSURE
The regulated outlet pressures, both low and high, have been
calibrated at the factory. Additional pressure adjustment
should not be necessary. If adjustment is necessary, set to
the following specifications. Check high pressure before
checking or adjusting low pressure. After adjustment, check
for gas leakage.
High Outlet Pressure Adjustment
1.
Turn off all electrical power to the system at main fuse or
circuit breaker. Close manual gas valve.
2.
Attach a manometer to the outlet pressure tap of the
valve.
3.
Turn on power and energize main and redundant (P.M.)
solenoids as well as the HI terminal. Open manual gas
valve.
4.
Remove high adjustment seal screw to expose the 3/32”
set screw, see Figure 11 on page 15.
5.
To
increase
outlet pressure, turn the 3/32” set screw
clockwise. To
decrease
outlet pressure, turn the set
screw counterclockwise. Adjust regulator until pressure
shown on manometer matches the pressure specified on
the appliance rating plate.
DO NOT
omit this test!
NEVER
use a flame to check
for gas leaks.
Be sure to relight any gas appliances that were
turned off at the start of this input check.
NATURAL GAS
Low Fire
1.6 IWG
High Fire
3.5 IWG
