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Gas piping leak check
Important: 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 makes three attempts to light before locking
out.
With the furnace in operation, check all of the pipe joints,
gas valve connections and manual valve connections for
leakage using an approved gas detector, a non-corrosive
leak detection fluid or other leak detection methods. Take
appropriate action to stop any leak. If a leak persists,
replace the faulty component.
The furnace and its equipment shut-off valve must be
disconnected from the gas supply during any pressure
testing of that system at test pressures in excess of 1/2 in.
psig (3.45 kPa).
The furnace must be isolated from the gas supply piping
system by closing the equipment shut-off valve during
any pressure testing of the gas supply system.
Ignition system sequence
1.
Turn the gas supply on at the external valve and
main gas valve.
2.
Set the thermostat above room temperature to call
for heat.
3.
System start-up occurs as follows:
a. The induced draft blower motor starts and
comes up to speed. Shortly after inducer start-
up, the hot surface igniter glows for about 17 s.
b. After this warm up, the ignition module
energizes (opens) the main gas valve.
c. Approximately 30 s after a flame is established,
the supply air blower starts.
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 makes three
attempts to light before locking out.
Important: With the furnace in operation,
check all of the pipe joints, gas valve
connections 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.
Calculating the furnace input (natural
gas)
28
Installation Manual: RL18 Single-Stage Standard ECM Residential Gas Furnaces (Non-condensing Multi-position Standard
Low NOx)
Burner orifices are sized to provide the correct input
rate using natural gas with a heating value of 1,030
Btu/cu ft (38.4 MJ/m
gas is significantly different, it may be necessary to
replace the orifices.
Do not set manifold pressure less than 3.2 in. W.C. or
more than 3.8 in. W.C. for natural gas at sea level. If
manifold pressure is outside this range, change main
burner orifices.
If orifice hole appears damaged or it is suspected
to have been redrilled, check orifice hole with a
numbered drill bit of correct size. Never redrill an
orifice. A burr-free and squarely aligned orifice hole is
essential for proper flame characteristics.
Do not bottom out gas valve regulator adjusting
screw. This can result in unregulated manifold
pressure and result in excess overfire and heat
exchanger failures.
Verify natural gas input rate by clocking the meter as
follows:
1.
Turn off all other gas appliances and pilots.
2.
Run the furnace for a minimum of 3 min in heating
operation.
3.
Measure time (in seconds) for the gas meter to
complete one revolution and note the reading. The
2 cu ft dial provides a more accurate measurement
of gas flow.
4.
See Table 9 for cubic feet of gas per hour.
5.
Multiply cubic feet per hour by heating value (Btu/
cu ft) to obtain input.
If the clocked rate does not match the input rate
from the unit nameplate, follow the steps in
Adjusting the manifold gas pressure and input
Johnson Controls Ducted Systems
NOTICE
3
). If the heating value of your
NOTICE
NOTICE
CAUTION
rate.
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