JOHNSON CONTROLS
48
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
SECTION 3 – START-UP
The heat section has two roll out switches mounted
above the burners. The purpose of the roll out switch
is to protect the gas heat section from flame roll out,
flame burning outside the heat exchanger. A restriction
in the heat exchanger or breach in the flue passages
could result in a roll out situation. The roll out switch
is a manual reset device.
The unit has two high temperature limit switches. One
located at the heat exchanger vestibule panel and the
other located in the area of the heat exchanger return
bend. These limits are automatic reset devices. If the
limit opens the ignition control will de-energize the gas
valve. On staged gas heat, as soon as the limit closes the
ignition control will re-initiate the ignition sequence. If
the limit opens on a modulating gas heat section the
IPU board locks out the heat section.
The control circuit is tested in the factory to insure that
all of these steps are followed, however, natural gas
is not actually introduced to the system in the plant;
nitrogen is used in its place.
Post Start Checks
When a signal is received at the gas heat control mod-
ule from the IPU board, verify:
• Combustion blower starts and runs for 30 seconds
before the spark is initiated.
• Spark igniter sparks.
• Gas valve opens.
• Burners light from right to left, in a 2.5-second
time frame.
• Each burner lights in sequential order from right
to left; and establishes stable flame immediately
upon ignition.
• No gas leaks in the unit piping as well as the sup-
ply piping.
• Correct manifold gas pressures.
See
Pressure Adjustment on page 49.
• The supply pressure is adequate. It must be within
the limitations shown in
•
The flame is stable, with the flame present only at
the end of the burner and that there isn't any burn-
ing occurring inside the burner.
Supply pressure should be checked with all
gas appliances in the building at full fire.
At no time should the standby gas pressure
exceed 10.5" W.C. or the operating pres-
sure drop below 4.5" W.C. for natural gas
or the standby gas pressure exceed 13.0"
W.C. or the operating pressure drop below
11.0" W.C. for propane. If the gas pressure
is outside these limits, contact the install-
ing mechanical contractor for corrective
action.
There should be a little yellow tipping of
the flame.
There may be some smoke through the
flue, due to tooling oil burning off of the
heat exchanger tubing.
TABLE 12 -
LOW FIRE / HIGH FIRE - STAGED
TYPE
OF
GAS
LINE PRESSURE
MANIFOLD
PRESSURE
MIN
MAX
LO FIRE +/-
0.3" W.C.
HI FIRE /-
0.3" W.C.
NATURAL 4.5" W.C. 10.5" W.C. 1.4" W.C. 3.5" W.C.
PROPANE 11.0" W.C. 13.0" W.C. 4.2" W.C. 10.0" W.C.
TABLE 13 -
LOW FIRE / HIGH FIRE - MODULATING
TYPE
OF
GAS
LINE PRESSURE
PRESSURE TO
MAXITROL VALVE
MIN
MAX
LO FIRE +/-
0.3" W.C.
HI FIRE+/-
0.3" W.C.
NATURAL 4.5" W.C. 10.5" W.C. 1.4" W.C. 3.5" W.C.
PROPANE 11.0" W.C. 13.0" W.C. 4.2" W.C. 10.0" W.C.
