5725848-XIM-A-0319
Johnson Controls Ducted Systems 43
Manifold gas pressure adjustment
Small adjustments to the high-fire gas flow may be made by
turning the pressure regulator adjusting screw on the automatic
gas valve.
Adjust as follows:
1. Remove the cap on the regulator. It's located next to the
push-on electrical terminals.
2. To decrease the gas pressure, turn the adjusting screw
counterclockwise.
3. To increase the gas pressure, turn the adjusting screw
clockwise.
NOTE: The correct manifold pressure for these furnaces is 872
± 74 Pa gauge (3.50 IWG ±0.3).
Pilot checkout
The pilot flame should envelope the end of the flame sensor. To
adjust pilot flame, (1) remove pilot adjustment cover screw, (2)
increase or decrease the clearance for air to the desired level,
(3) be sure to replace cover screw after adjustment to prevent
possible gas leakage.
Put the system into operation and observe through complete
cycle to be sure all controls function properly.
Burner instructions
To check or change burners, pilot or orifices, CLOSE MAIN
MANUAL SHUT-OFF VALVE AND SHUT OFF ALL ELECTRIC
POWER TO THE UNIT.
1. Remove the screws holding either end of the manifold to
the burner supports.
2. Open the union fitting in the gas supply line just upstream
of the unit gas valve and downstream from the main
manual shut-off valve.
3. Remove the gas piping closure panel.
4. Disconnect wiring to the gas valves and spark ignitors.
Remove the manifold-burner gas valve assembly by lifting
up and pulling back.
Burners are now accessible for service.
Reverse the above procedure to replace the assemblies. Make
sure that burners are level and seat at the rear of the heat
exchanger.
Burner air shutter adjustment
Adjust burner shutters so no yellow flame is observed in the
heat exchanger tubes.
Checking gas input
Natural gas
1. Turn off all other gas appliances connected to the gas
meter.
2. With the furnace turned on, measure the time needed for
one revolution of the hand on the smallest dial on the
Figure 23: Typical valves
Figure 24: Proper flame adjustment
Figure 25: Typical flame appearance
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