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Gas Pressure Adjustment
Gas Flow (Approximate)
TABLE 9
GAS METER CLOCKING CHART
Unit
Seconds for One Revolution
Natural
LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
−045
80
160
200
400
−070
55
110
136
272
−090
41
82
102
204
−110
33
66
82
164
−135
27
54
68
136
Natural−1000 btu/cu ft LP−2500 btu/cu ft
Furnace should operate at least 5 minutes before check-
ing gas flow. Determine time in seconds for
two
revolu-
tions of gas through the meter. (Two revolutions assures a
more accurate time.)
Divide by two
and compare to time
in table 9 below. If manifold pressure matches table 10
and rate is incorrect, check gas orifices for proper size and
restriction. Remove temporary gas meter if installed.
NOTE
− To obtain accurate reading, shut off all other gas
appliances connected to meter.
Supply Pressure Measurement
When testing supply gas pressure, use the 1/8" N.P.T.
plugged tap or pressure post located on the gas valve to
facilitate test gauge connection. See figure 59. Check gas
line pressure with unit firing at maximum rate. Low pres-
sure may result in erratic operation or underfire. High pres-
sure can result in permanent damage to gas valve or over-
fire.
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres-
sure must fall within range listed in table 10.
Manifold Pressure Measurement
1 − Remove the threaded plug from the outlet side of the
gas valve and install a field−provided barbed fitting.
Connect to a manometer to measure manifold pres-
sure.
2 − Start unit and allow 5 minutes for unit to reach steady
state.
3 − While waiting for the unit to stabilize, observe the
flame. Flame should be stable and should not lift from
burner. Natural gas should burn blue.
4 − After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
10.
NOTE
− Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
TABLE 10
Supply Line and Manifold Pressure (inches w.c.)
Unit
Fuel
Manifold
Pressure
Line Pressure
All
Nat. Gas
3.5
4.5 − 10.5
All
L.P. Gas
10.0
11.0 − 13.0
NOTE
− A natural to L.P. propane gas changeover kit is nec-
essary to convert this unit. Refer to the changeover kit
installation instruction for the conversion procedure.
Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com-
bustion. Take combustion sample beyond the flue outlet
and compare to the tables below.
TABLE 11
Unit
CO
2
%
For Nat
CO
2
%
For L.P.
−045
7.2 − 7.9
8.6 − 9.3
−070
−090
−110
−135
The maximum carbon monoxide reading should not exceed 50 ppm.
High Altitude
NOTE
− In Canada, certification for installations at eleva-
tions over 4500 feet (1372 m) is the jurisdiction of local au-
thorities.
92AF1UH/95AF1UH units require no manifold pressure
adjustments for operation at altitudes up to 10,000 feet
(3048 m) above sea level. Units installed at altitude of 4501
− 10,000 feet (1373 to 3048m) require a pressure switch
change which can be ordered separately. Table 12 lists
conversion kit and pressure switch requirements at varying
altitudes.
The combustion air pressure switch is factory−set and re-
quires no adjustment.
