GF - D 13
Gas Valves
Step 11
Set the furnace in the CONTINGENCY MODE of
operation at the User Interface Module for the third
stage of heat with a 50% duty cycle, then depower
and then repower the furnace.
Step 12
Let the furnace go through the third stage learning
routine and its temperature rise to stabilize. This
temperature rise and learning routine will take three
minutes.
Step 13
Remove the dust cap and adjust the gas valve third
stage of heat pressure adjustment screw (Figure 34),
slightly to obtain the correct rate.
THIRD STAGE ADJUSTMENT:
COUNTERCLOCKWISE TO DECREASE OR
CLOCKWISE TO INCREASE PRESSURE.
Figure 33
NOTE: The dust cap screw covering the third stage
pressure adjustment screw must be in place during
manifold gas pressure readings.
Figure 34
Step 14
Replace and tighten the dust cap for the third stage
adjustment screw and then read the manifold pressure
again. This procedure may need to be repeated until
the manifold gas pressure is 3.5" of Water Column
pressure (Figure 35).
Figure 35
Step 15
If the firing rate cannot be obtained with the manifold
pressures specified in Table 7, check inlet gas piping
for proper sizing and pressure. If insufficient, correct
and/or contact gas company to adjust input pressure.
Step 16
Once the third stage gas pressure is adjusted, turn
the gas valve switch to the OFF position (Figure 36).
Operate the furnace for two more minutes to cool down
the heat exchanger.
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