36
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)
G
AS
M
ANIFOLD
P
RESSURE
M
EASUREMENT
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 pres-
sure boss plug. Install an 1/8" NPT hose barb fitting into
the outlet pressure tap.
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” con-
tacts to provide a call for low stage heat.
7. Modulating furnaces light at 80% of max input. For natu-
ral gas the expected manifold pressure at ignition will
be in a range of 1.8" - 2.5" WC. For LP gas the range will
be 5.8" - 6.8" WC.
NOTE: Measure the gas manifold pressure with the burn-
ers firing. After every time the main power is turned
off and back on, the furnace will enter a calibration rou-
tine on the next call for heat
The inducer will ramp up
and down during the calibration routine. After calibra-
tion, the furnace will proceed to ignition cycle.
F
URNACE
M
ANIFOLD
P
RESSURES
35%
=
.5" WC
35%
=
1.2" WC
50%
=
.9" WC
50%
=
2.5" WC
60%
=
1.25" WC
60%
=
3.7" WC
70%
=
1.70" WC
70%
=
5.0" WC
80%
=
2.20" WC
80%
=
6.5" WC
90%
=
2.80" WC
90%
=
8.0" WC
100%
=
3.50" WC
100%
=
10.0" WC
NATURAL GAS
L.P. GAS
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 routine.
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”, press-
ing and holding the Fault Recall Push-Button for 3 sec-
onds will enable the field test mode and override the
normal firing rate sequence at a rate of 100% for 5 min-
utes 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 re-
vert back to normal.
9. Turn off all electrical power and gas supply to the sys-
tem.
10. Remove the manometer hose from the hose barb fit-
ting.
11. 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.
12. Turn on electrical power and gas supply to the system.
13. Close thermostat contacts “R” and “W1/W2” to ener-
gize the valve.
Using a leak detection solution or soap suds, check for leaks at
outlet pressure boss plug. Bubbles forming indicate a leak.
SHUT OFF GAS AND REPAIR ALL LEAKS IMMEDIATELY!
NOTE:
For natural gas to LP conversion, consult the furnace
Specification Sheet.
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
G
AS
I
NPUT
R
ATE
M
EASUREMENT
(N
ATURAL
G
AS
O
NLY
)
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.
OPERATION
