Gas Furnaces:Combustion Air Adjustment

Combustion Air Adjustment

Primary air shutters are provided on all furnaces to enable adjustment of the primary air supply. The purpose of this adjustment is to obtain the most suitable flame characteristics.

Experience has shown that the most efficient burner flame for natural gas has a soft blue cone without a yellow tip. For pro- pane gas, there should be a little yellow showing in the tips of the flame.

The procedure for adjusting the primary air on a Coleman gas furnace may be summarized as follows:

1. Light the pilot burner.

2. Turn up the setting on the room thermostat until the main burners come on.

3. Allow the main burners 10 minutes to warm up.

4. Loosen locknut on adjusting screw (Figure 11-42).

5. Turn adjusting screw in (clockwise) until the yellow tip appears in the flame.

6. Turn adjusting screw out (counterclockwise) until the yellow tip just disappears.

7. Hold adjusting screw and tighten locknut.

8. Repeat Steps 4 through 7 on each of the other burners.

On a Fedders gas furnace, a locking screw is located above the primary air opening on each gas burner (Figure 11-43). The primary air adjustment procedure is as follows:

1. Loosen the locking screw at the base of the burner.

2. Adjust the air-shutter opening to a position that gives a slight yellow tip on the end of the flame.

3. Open the air shutter until the yellow tip just disappears.

4. Tighten the locking screw.

5. Repeat Steps 1 through 4 for each of the burners.

A primary air-shutter assembly is provided on all Carrier gas furnaces in order to simplify the adjustment procedure. As shown in Figure 11-44, adjustment of the end burner results in a simultaneous adjustment of all burners.

After the primary air adjustments have been made, check to see that the burners are level. The burner flames should be uniform and centered in the heat exchanger (see Heat Exchanger in this chapter).

Before allowing the furnace to continue operating, you must check to see that it has the proper draft. This can be done by passing a match along the draft-hood opening. If the vent is drawing properly, the match flame will be drawn inward (that is, into the draft hood). If the furnace is not receiving proper draft, the products of combustion escaping the draft hood will extinguish the flame. The draft must be corrected before the furnace is operated.

TROUBLESHOOTING USING CONTROL SCHEMATICS:THE HOPSCOTCH METHOD

Troubleshooting Using Control Schematics:A Commercial Air Conditioning Unit

Gas and Oil Controls:Cadmium Cell Primary Controls

Pipework and oil traps:Oil traps

Steam and Hydronic Line Controls:Tilting Traps and Lifting Traps

REFRIGERATION EQUIPMENT AND PROCESSES:FOULING, SCALING, AND CORROSION

Ventilation Principles:Ridge Ventilators

Radiators, Convectors, and Unit Heaters:Installing Electric Baseboard Heaters

Basic Open System Cycles:Vapor Refrigeration/Heat Pump Cycle.