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Measuring Inlet Gas Pressure Alternate Method
A
B
G
A. Gas supply line
B. Gas shutoff valve
C. Gas supply line to furnace
D. Open to atmosphere
Manifold Pressure Check
1. Turn off gas supply to furnace at the manual gas shutoff valve
external to the furnace.
2. Disconnect all electrical power to the system.
3. Loosen outlet pressure test screw (inlet/outlet pressure boss)
1 turn.
NOTE: Turn counterclockwise, and not more than 1 turn.
4. Connect a calibrated water manometer and ⁵⁄₁₆" hose to the
outlet pressure boss on the gas control valve. The hose
should overlap by ³⁄₈" (1 cm).
5. Turn on the gas supply.
6. Reconnect all electrical power to the system.
7. Turn on the system power and energize the main (M)
solenoid.
NOTE: Do not energize the HI solenoid.
8. Measure the gas manifold pressure with the burners firing.
9. Adjust manifold pressure using the Manifold Gas Pressure
chart.
Manifold Gas Pressure
Gas
Natural Gas
Low Stage
High Stage
Propane Gas
Low Stage
High Stage
10. Remove the regulator cover screw from the low-fire (LO)
regulator adjust tower and turn the screw clockwise to
increase pressure, or counterclockwise to decrease pressure.
11. Energize the main (M) solenoid as well as the HI terminal.
16
C
D
F
E
E. Manometer
F. Manometer hose
G. Dripleg cap with fitting
Range
Nominal
1.6" to 2.2" W.C.
2.0" W.C.
3.2" to 3.8" W.C.
3.5" W.C.
5.7" to 6.3" W.C.
6.0" W.C.
9.7" to 10.3" W.C.
10.0" W.C.
12. Remove the regulator cover screw from the high-fire (HI)
regulator adjust tower, and turn the screw clockwise to
increase pressure, or counterclockwise to decrease pressure.
13. Disconnect all electrical power, and turn off the gas supply to
the system.
14. Remove the manometer hose from the outlet pressure boss.
15. Tighten (clockwise, 7 in.-lb minimum) the outlet pressure test
screw to seal the pressure port.
16. Reconnect the electrical power, and turn on the gas supply to
the system.
17. Turn on the system power and energize valve.
18. Using a leak detection solution or non-chlorine soap suds,
check for leaks at the hose connection.
IMPORTANT: Bubbles forming indicate a leak. Turn off gas
immediately and fix all leaks.
NOTE: For gas-to-gas conversion, consult your dealer for the
appropriate conversion.
Gas Input Check—Natural Gas Only
To measure the gas input, use a gas meter and proceed as
follows:
1. Turn off the gas supply to all other appliances except the unit.
2. With the unit operating, time the smallest dial on the meter for
1 complete revolution. If this is a 2 cu ft dial, divide the
seconds by 2; if it is a 1 cu ft dial, use the seconds as is. This
gives the seconds per cubic foot of gas being delivered to the
unit.
3. Input = Gas Heating Value x 3,600 / Sec. Per Cubic Foot
Example: Natural gas with a heating value of 1,000 Btu per
cubic foot and 34 seconds per cubic foot as determined by
Step 2, then:
Input = 1,000 x 3,600 / 34 = 106,000 Btu/h.
NOTE: Btu content of the gas should be obtained from the
gas supplier. This measured input must not be greater than
shown on the unit rating plate.
4. Turn on the gas supply to all other appliances turned off in
Step 1. Check that all pilot burners are operating.
Main Burner Flame Check
Flames should be stable, soft and blue (dust may cause orange
tips, but they must not be yellow) and extending directly outward
from the burner without curling, floating or lifting off.
Measure Temperature Rise
Check the temperature rise through the unit by placing
thermometers in supply and return air registers as close to the
unit as possible. Thermometers must not be able to sample
temperature directly from the unit heat exchangers, or false
readings could be obtained.
1. All registers must be open; all duct dampers must be in their
final (fully or partially open) position and the unit operated for
15 minutes before taking readings.
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