43
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!
G
AS
I
NPUT
R
ATE
M
EASUREMENT
(N
ATURAL
G
AS
O
NLY
)
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.
2. While the furnace is operating at high fire rate, time and record one complete revolution of the gas meter dial measuring the
smallest quantity, usually the dial that indicates 1/2 cu. ft. per revolution. You will use this number to calculate the
quantity of gas in cubic ft. if the furnace would consume if it ran steadily for one hour (3600 seconds).
3. If the 1/2 cu. ft. dial was used, multiply your number x 2.
EXAMPLE: If it took 23 seconds to complete one revolution of the 1/2 ft. dial.
This tells us that at this rate, it would take 46 seconds to consume one cu. ft. of gas. 23 x 2 = seonds per cu. ft.
3600 (secs in 1 hour) / 46 = 78
This tells us that in one hour, the furnace would consume 78 cu. ft. of gas.
The typical caloric range for 1 cu. ft. of natural gas is around 1000 BTU. Check with your gas utility, if possible. In this
example, the furnace is consuming 78,000 BTUH.
NOTE:
The final manifold pressure cannot vary by more than ± 0.3” w.c. for Natural and + 0.5” for LP from the specified
setting. Consult your local gas supplier if additional input rate adjustment is required.
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
