Two Stage Gas Furnace, High-Fire Adjustment

The volume of air supplied by the combustion blower deter- mines the amount of oxygen available for combustion, while the manifold gas pressure establishes fuel input. By mea- suring the percentage of carbon dioxide produced as a by- product of combustion, the operator can estimate the amount of oxygen used and modify the air volume or the gas pressure to obtain the proper air/fuel ratio.

Arriving at the correct air/fuel mixture for a furnace results in rated burner output, limited production of carbon monoxide, and a steady flame that minimizes nuisance shutdowns.

WARNING

Hazardous Gases and Flammable Vapors!

Exposure to hazardous gases from fuel substances have been shown to cause cancer, birth defects or other reproductive harm. Improper installation, adjust- ment, alteration, service or use of this product could cause flammable mixtures. To avoid hazardous gases and flammable vapors follow proper installation and set up of this product and all warnings as provided in this manual. Failure to follow all instructions could result in death or serious injury.

When using dry nitrogen cylinders for pressurizing units for leak testing, always provide a pressure regula- tor on the cylinder to prevent excessively high unit pressures. Never pressurize unit above the maximum recommended unit test pressure as specified in appli- cable unit literature. Failure to properly regulate pres- sure could result in a violent explosion, which could re- sult in death or serious injury or equipment or prop- erty-only-damage.

Two Stage Gas Furnace

High-Fire Adjustment

1.Use Table 4-1 to program the following system compo- nents for operation by scrolling through the Human Inter- face displays;

Gas Heat

Supply Fan (On)

Inlet Guide Vanes (100% Open, if applicable) Variable Frequency Drive (100% Output, if applicable)

RTM Occ/Unocc Output (Unoccupied) Heat Stages 1 & 2 (On)

Turn the 115 volt control circuit switch 4S24 located in the heater control panel to the "On" position.

Open the manual gas valve, located in the gas heat section.

2.Once the configuration for the appropriate heating sys- tem is complete, press the NEXT key until the LCD dis- plays the “Start test in __Sec.” screen. Press the + key to designate the delay before the test is to start. This ser- vice test will begin after the TEST START key is pressed and the delay designated in this step has elapsed. Press the ENTER key to confirm this choice.

3.Press the TEST START key to start the test. Remember that the delay designated in step 2 must elapse before the system will begin to operate.

4.Once the system has started, check the appearance of the flame through the sight glass provided on the front of

Unit Start-Up (Continued)

the heat exchanger. In appearance, a normal flame has a clearly defined shape, and is primarily (75%) blue in color with an orange tip.

5.Check the manifold gas pressure by using the manifold pressure port on the gas valve. Refer to Table 4-7 for the required manifold pressure for high-fire operation. If it needs adjusting, remove the cap covering the high-fire adjustment screw on the gas valve. Refer to Figure 4-8 for the adjustment screw location. Turn the screw clock- wise to increase the gas pressure or counterclockwise to decrease the gas pressure.

6.Use a carbon dioxide analyzer and measure the percent- age of carbon dioxide in the flue gas. Refer to the illus- tration in Figure 4-7. Take several samples to assure that an accurate reading is obtained. Refer to Table 4-7 for the proper carbon dioxide levels. A carbon dioxide level exceeding the listed range indicates incomplete combus- tion due to inadequate air or excessive gas.

Combustion Air Adjustment (O2 )

7.Use an oxygen analyzer and measure the percentage of oxygen in the flue gas. Take several samples to assure an accurate reading. Compare the measured oxygen level to the combustion curve in Table 4-8. The oxygen content of the flue gas should be 4% to 5%. If the oxygen level is outside this range, adjust the combustion air damper to increase or decrease the amount of air enter- ing the combustion chamber. Refer to Figure 4-10 for the location of the combustion air damper .

8.Recheck the oxygen and carbon dioxide levels after each adjustment. After completing the high-fire checkout and adjustment procedure, the low-fire setting may require adjusting.

Low-Fire Adjustment

(500 MBH, 850 & 1,000 MBH only)

1.Use the TEST initiation procedures outlined in the previ- ous section to operate the furnace in the low-fire state (1st Stage).

2.Use a carbon dioxide analyzer and measure the percent- age of carbon dioxide in the flue gas. Refer to the illus- tration in Figure 4-7, Inset A. Take several samples to as- sure that an accurate reading is obtained. Refer to Table 4-8 for the proper carbon dioxide levels. If the measured carbon dioxide level is within the listed values, no adjustment is necessary. A carbon dioxide level ex- ceeding the listed range indicates incomplete combus- tion due to inadequate air or excessive gas.

3.Check the manifold gas pressure by using the manifold pressure port on the gas valve. Refer to Table 4-8 for the required manifold pressure during low-fire operation. If it needs adjusting, remove the cap covering the low-fire adjustment screw on the gas valve. Refer to Figure 4-8 for the adjustment screw location. Turn the screw clock- wise to increase the gas pressure or counterclockwise to decrease the gas pressure.

Note: Do not adjust the combustion air damper while the furnace is operating at low-fire.

4.Check the carbon dioxide levels after each adjustment.

5.Press the STOP key at the Human Interface Module in the unit control panel to stop the system operation.