35
8. Adjust manifold pressure using the following Manifold Gas
Pressure chart.
9. Remove the regulator cover screw from the low (LO) outlet
pressure regulator adjust tower.
10. Turn the screw clockwise to increase pressure or
counterclockwise to decrease pressure.
11. Replace regulator cover screw.
12. Close thermostat R and W2 contacts to provide a call for
high-stage heat.
13. Remove the regulator cover screw from the high (HI) outlet
pressure regulator adjust tower.
14. Turn the screw clockwise to increase pressure or
counterclockwise to decrease pressure.
15. Replace the regulator cover screw.
16. Turn off all electrical power and gas supply to the system.
17. Remove the manometer hose from the hose barb fitting or
outlet pressure boss.
18. Replace the outlet pressure tap:
■
Honeywell VR9205 valve: Remove the
¹⁄₈
" NPT hose barb
fitting from the outlet pressure tap. Replace the outlet
pressure boss plug and seal with a high quality thread
sealer.
■
White-Rodgers 36G54 valve: Turn the outlet pressure test
screw in to seal pressure port (clockwise, 7 in-lb
minimum).
19. Turn on electrical power and gas supply to the system.
20. Close the thermostat contacts R and W1/W2 to energize the
valve.
21. Using a leak detection solution or soap suds, check for leaks
at the outlet pressure boss plug (Honeywell valve) or screw
(White-Rodgers valve). Bubbles forming indicate a leak.
IMPORTANT: If a leak is detected, turn off gas immediately
and repair all leaks.
NOTE: For gas-to-gas conversion, consult your dealer for
appropriate conversion.
Gas Input Rate Measurement—Natural Gas Only
The gas input rate to the furnace must never be greater than that
specified on the unit rating plate. To measure Natural gas input
using the gas meter, use the following procedure.
1. Turn off the gas supply to all other gas-burning appliances
except the furnace.
2. While the furnace is operating, time and record one complete
revolution of the smallest gas meter dial.
3. Calculate the number of seconds per cubic foot (sec/ft
3
) of
gas being delivered to the furnace. If the dial is a one cubic
foot dial, divide the number of seconds recorded in Step 2 by
one. If the dial is a 2 cubic foot dial, divide the number of
seconds recorded in Step 2 by 2.
4. Calculate the furnace input in Btu per hour (Btu/h). Input
equals the sum of the installation’s gas heating value and a
conversion factor (hours to seconds) divided by the number
of seconds per cubic foot. The measured input must not be
greater than the input indicated on the unit rating plate.
Example: Installation’s gas heating (HTG) value: 1,000 Btu/ft
3
(Obtained from gas supplier)
Installation’s seconds per cubic foot: 34 sec/ft
3
Conversion Factor (hours to seconds): 3,600 sec/h
Input = (Htg. value x 3,600) ÷ seconds per cubic foot
Input = (1,000 Btu/ft
3
x 3,600 sec/h) ÷ 34 sec/ft
3
Input = 106,000 Btu/h
This measured input must not be greater than the input indicated
on the unit rating plate.
5. Turn on the gas supply to all other appliances turned off in
Step 1.
6. Ensure that all appliances are functioning properly and that all
pilot burners are lit and operating.
Temperature Rise
Temperature rise must be within the range specified on the unit
rating plate. An incorrect temperature rise may result in
condensing in or overheating of the heat exchanger. An airflow
and temperature rise table is provided in the Specification Sheet
applicable to your model. Determine and adjust temperature rise
as follows:
1. Operate furnace with burners firing for approximately
10 minutes.
2. Ensure that all registers are open and all duct dampers are in
their final (fully or partially open) position.
3. Place thermometers in the return and supply ducts as close
to the furnace as possible. Thermometers must not be
influenced by radiant heat from the heat exchanger.
Temperature Rise Measurement
Rise = Supply air temperature - Return air temperature
4. Subtract the return air temperature from the supply air
temperature to determine the air temperature rise. Allow
adequate time for thermometer readings to stabilize.
5. Adjust the temperature rise by adjusting the circulator blower
speed. Increase blower speed to reduce temperature rise.
Decrease blower speed to increase temperature rise. Refer to
“Circulator Blower Speeds” for speed changing details.
Manifold Gas Pressure
Gas
Range
Nominal
Natural
Low Stage
1.7" to 2.3" W.C.
2.0" W.C.
High Stage
3.2" to 3.8" W.C.
3.5" W.C.
Propane
Low Stage
5.7" to 6.3" W.C.
6.0" W.C.
High Stage
9.7" to 10.3" W.C.
10.0" W.C.
A. Heat exchanger radiation
“line of sight”
B. Supply air
C. Supply air temperature
D. Return air temperature
E. Return air
A
B
C
D
E
