2 Maintenance
Adjusting combustion air pressure
The following is a recommended method for setting the combustion air pressure. The following pressure settings are for installations up to 4000 feet altitude. Contact the factory for high altitude air pressure settings.
Upon removal of the upper front doors, locate the capped tee in the pressure tubing that connects between the inner top and the gas valves. Remove this cap and connect a hose from the tee to a manometer.
For 399,999 - 750,000 Btu/hr models (reference FIG.
1.The combustion air chamber pressure for these models is typically 1.2 - 1.3 inches water column when the fan is at high speed.
2.If adjustment is necessary, slightly loosen the nuts connecting the fan to the inner top.
3.Adjust the air shutter located underneath the fan assembly to obtain the desired chamber pressure. Slide the shutter inward to decrease the chamber pressure or outward to increase the chamber pressure.
For 990,000 - 2,070,000 Btu/hr models (reference FIG.
1.The combustion air chamber pressure for these models is typically 1.2 - 1.3 inches water column when the fan is at high speed.
2.If adjustment is necessary, slightly loosen the nut located on the air shutter arm.
3.Adjust the air shutter arm to obtain the desired chamber pressure. Slide the arm inward to decrease the chamber pressure or outward to increase the chamber pressure.
All models
4.Once the adjustment procedure is complete, tighten all connections, disconnect the manometer, and replace the cap at the tee.
5.Check all connections and test fire the unit.
6.Replace all panels.
Checking manifold gas pressure
The gas regulator on the combination gas valve is adjustable to supply the proper manifold pressure for normal operation. The gas valves are factory
Gas manifold pressures may be checked with the use of a manometer. Follow the steps in the Checking Combustion Air Pressure Section prior to checking the manifold pressures.
Checking manifold gas pressure
1.Turn the appliance power switch to the “OFF” position.
2.Remove the upper outer access panels.
3.Remove the 1/8" hex plug from the downstream side of the gas valve (see FIG.
4.Connect a hose from the tee used to measure the combustion air pressure to the other side of the manometer.
5.Turn the appliance power switch to the “ON” position.
6.With the unit at high fire, check and record the manifold pressure of the valve. The manifold pressure will be the sum of the two pressure readings (reference Table 2B).
7.Repeat this process with each gas valve.
WARNING Overfire and underfire hazards! Possible fire, explosion, overheating, and component failure. Do not attempt to adjust firing rate of the appliance. The firing rate must be adjusted only by factory trained personnel.
If you must adjust the gas valve regulator pressure, follow the steps below:
1.Remove the cap covering the manifold pressure adjustment screw (see FIG.
2.Make a slight adjustment to the manifold pressure adjustment screw. Turning the screw clockwise increases manifold pressure and counterclockwise decreases manifold pressure.
3.Replace the cap and check the manifold pressure. Note: Allow the unit to
4.Repeat the steps above to match the manifold pressures from Table 2B.
5.Once the adjustment procedure is complete, turn off the appliance, disconnect the manometer, replace and tighten all connections, and replace all panels.
6.Turn on the appliance and test fire the unit.
7.Repeat this process with each gas valve.
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