Installation Guide

42
If supply pressure differs from table, make the necessary adjustments to pressure
regulator, gas piping size, etc., and/or consult with local gas utility.
5. Turn OFF gas to furnace at the manual shutoff valve and disconnect manometer.
Reinstall threaded plug before turning on gas to furnace.
6. Turn OFF any unnecessary gas appliances stated in step 3.
GAS MANIFOLD PRESSURE MEASUREMENT
T O PREVENT UNRELIABLE OPERATION OR EQUIPMENT DAMAGE , THE
GAS MANIFOLD PRESSURE MUST BE AS SPECIFIED ON THE UNIT RATING
PLATE . G AS VALVE IS FACTORY SET AND DOES NOT REQUIRE ANY
F IELD ADJUSTMENT . D O NOT ATTEMPT TO ADJUST VALVE .
CAUTION
The manifold pressure must be measured with the burners operating. To measure
the manifold pressure, use the following procedure:
1. Turn OFF gas to furnace at the manual gas shutoff valve external to the furnace.
2. Turn off all electrical power to the system.
3. Outlet pressure tap connections: Remove the outlet pressure tap plug. Install
an 1/8" NPT hose barb fitting into the outlet pressure tap. Refer to gas valve
diagram on preceding page.
4. Attach a hose and manometer to the outlet pressure barb fitting.
5. Turn ON the gas supply.
6. Turn on power and close thermostat “R” and “W1” contacts to provide a call for low stage heat.
7. Modulating furnaces light at 80% of max input. For natural gas, the expected manifold pressure at ignition will be in a
range of 1.8” - 2.5” W.C. For LP gas, the range will be 5.8” - 6.8” W.C.
NOTE: Measure the gas manifold pressure with the burners firing. After every time the main power is turned off and
back on, the furnace will enter a calibration routine on the next call for heat The inducer will ramp up and down during
the calibration routine. After calibration, the furnace will proceed to ignition cycle.
8. Field Test Mode is intended to help a service person troubleshoot and check out an installed appliance by bringing the
furnace up to High fire (100% input), by-passing the normal modulating routing.
To enter Field Test Mode the Fault Recall Push-Button must be pressed twice within a 5 second period at any time
during a heating cycle, at which time the display will show “Ft”. While the display is showing “Ft”, pressing and
holding the Fault Recall Push-Button for 3 seconds will enable the field test mode and override the normal firing rate
sequence at a rate of 100% for 5 minutes or until the end of the call for heat. The display will show the normal “Hi”
while the control is firing at 100%. If the Fault Recall Push-Button has not been pressed within 5 seconds of displaying
“Ft” the display will revert back to normal.
NOTE: Gas valve is factory set and does NOT require
any field adjustment. Do NOT attempt to adjust valve.
9. Turn off all electrical power and gas supply to the system.
10. Remove the manometer hose from the hose barb fitting.
11. Remove the 1/8" NPT hose barb fitting from the outlet pressure tap. Replace the outlet pressure tap plug and seal with a high
quality thread sealer.
12. Turn on electrical power and gas supply to the system.
13. Close thermostat contacts “R” and “W1/W2” to energize the valve.
Using an approved liquid gas leak detector solution, check for leaks
at outlet pressure tap plug. Bubbles forming indicate a leak. SHUT OFF
GAS AND REPAIR ALL LEAKS IMMEDIATELY!
GAS INPUT RATE MEASUREMENT (NATURAL GAS ONLY)
The actual 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.
Gas Line
Gas
Shutoff
Valve
Gas Line
To Furnace
Drip Leg Cap
With Fitting
Manometer Hose
Manometer
Open To
Atmosphere
Measuring Inlet Gas Pressure (Alt. Method)
Figure 50
Range Nominal
Natural High Stage 3.2 - 3.8" w.c. 3.5" w.c.
Propane High Stage 9.5 - 10.5" w.c. 10.0" w.c.
Manifold Gas Pressure
Gas