Use the following procedure to determine the firing rate:
1.Shut off all other gas fired appliances.
2.Start the furnace and allow it to run for at least three minutes.
3.Measure the time (in seconds) required for the gas meter to complete one revolution.
4.Convert the time per revolution to cubic feet of gas per hour using Table 12.
5.Multiply the gas flow rate in cubic feet per hour by the heating value of the gas in Btu per cubic foot to obtain the firing rate in Btuh. Example:
•Time for 1 revolution of a gas meter with a 1 cubic foot dial = 40 seconds.
•From Table 9 read 90 cubic feet per hour of gas.
•Heating value of the gas (obtained from gas supplier) = 1040 Btu per cubic foot.
•Firing rate = 1040 x 90 = 93,600 Btuh.
6.Adjustments to the firing rate can be made by adjusting the gas manifold pressure. See the High Altitude Application section for additional information of firing rate at elevations above 2000 ft.
The manifold pressure must be set to the appro- priate value for your installation. Refer to either Table 7 for natural gas or Table 8 for LP/propane gas to verify the manifold pressure setting re- quired for your particular installation. To adjust the manifold pressure, remove the regulator cap and turn the adjusting screw clockwise to in- crease pressure or counterclockwise to reduce pressure. Replace the regulator cap after adjust- ments are complete.
!CAUTION:
Do not
Verifying and Adjusting
Temperature Rise
Verify that the temperature rise through the furnace is within the range specified on the furnace rating plate. Temperature rises outside the specified range could result in premature heat exchanger failure.
Place thermometers in the return and supply air stream as close to the furnace as possible. The
thermometer on the supply air side must be shielded from direct radiation from the heat exchanger to avoid false readings. Adjust all registers and duct dampers to the desired posi- tion and run the furnace for fifteen minutes before taking any temperature readings. The temperature rise is the difference between the supply and return air temperatures.
For typical duct systems, the temperature rise will fall within the range specified on the rating plate with the blower speed at the factory recom- mended setting. If the temperature rise mea- sured is outside the range specified, it may be necessary to change the blower speed. Lower blower speeds will increase the temperature rise and higher blower speeds will decrease the temperature rise.
The furnace is equipped with a multispeed mo- tor. Heating and cooling speed selection is made by moving the leads on the integrated control board located in the furnace. The wiring diagram on the furnace and Figures 25, 26 and 27 show the speed taps for adjusting motor speed.
If it is desired that the blower operate at the same speed for heating and cooling, tape off the terminal of the unused blower wire. Install the jumper wire, found in the plastic instruction bag, across the HEAT and COOL taps on the control board. Reconnect the desired blower tap to the piggyback quick connect.
The blower control is designed to start the circulating air blower 30 seconds after the gas valve is opened. The blower control is factory wired to turn the blower motor off 120 seconds after the gas valve is closed. This timing can be changed using the BLOWER OFF timing switch opposite the terminal block on the control board. (See Figure 25.)
Verifying Burner Operation
To verify operation of the burners, make sure that the blower compartment door is in place and that there is power to the furnace. Set the thermostat above room temperature and ob- serve the ignition sequence. The flame can be observed through the small clear window on the burner box. The burner flame should carry over between all burners. The flames should be blue, without yellow tips. Flames should extend from each burner without lifting, curling, or floating. After verifying ignition, set the thermostat below room temperature and verify that the burner flame extinguishes completely.
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