Lennox G50UHX Series Unit Information page 28

When checking piping connections for gas leaks, use pre-
ferred means. Kitchen detergents can cause harmful corro-
sion on various metals used in gas piping. Use of a specialty
Gas Leak Detector is strongly recommended. It is available
through Lennox under part number 31B2001. See Corp.
8411−L10, for further details.
Do not use matches, candles, flame or any other source of
ignition to check for gas leaks.
D−Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to
inlet pressure tap (field provided). See figure 18. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas valve or
overfire. See table 13 for operating pressure at unit gas
connection (line).
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres-
sure must fall within range listed in previous paragraph.
E−Check Manifold Pressure
After line pressure has been checked and adjusted, check
manifold pressure. Move pressure gauge to outlet pres-
sure tap located on unit gas valve (GV1). Checks of man-
ifold pressure are made as verification of proper regulator ad-
justment. Manifold pressure for the G50UH(X) can be mea-
sured at any time the gas valve is open and is supplying gas
to the unit. See table 13 for normal operating manifold pres-
sure.
TABLE 13
All G50UH Units
Line Pressure WC"
Manifold Pressure WC"
IMPORTANT
For safety, connect a shut-off valve between the
manometer and the gas tap to permit shut off of
gas pressure to the manometer.
The gas valve is factory set and should not require adjust-
ment. All gas valves are factory regulated. See specifica-
tions section of this manual for High Altitude manifold pres-
sure settings.
Manifold Adjustment Procedure:
1 − Connect a test gauge to outlet pressure tap on gas
valve. See figures 15, 16 and 17. Start unit and allow 5
minutes for unit to reach steady state.
2 − While waiting for the unit to stabilize, notice the flame.
Flame should be stable and should not lift from burner.
Natural gas should burn blue. L.P. gas should burn
mostly blue with some orange streaks.
3 − After allowing unit to stabilize for 5 minutes, record
manifold pressure.
Natural LP
4.5 − 10.5 11.0 − 13.0
3.5 10.0
NOTE−Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to
replace pressure tap plug.
F− Proper Gas Flow (Approximate)
& Combustion
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 14 below. If manifold pressure matches table 13
and rate is incorrect, check gas orifices for proper size
and restriction. After furnace has been in operation for 15
minutes, take a combustion sample beyond the flue out-
let. Compare to table 15 .
NOTE− To obtain accurate reading, shut off all other gas
appliances connected to meter.
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
G50UH G50UH
Unit 1 cu ft
Dial
−45 82
−70 55
−90 41
−110 33
−135 27
−155 23
Natural−1000 btu/cu ft
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
G50UH Unit CO
24A−045(X) 5.50 − 6.50
24A−070 7.00 − 8.00
36A−070(X) 6.80 − 7.80
36B−090 7.20 − 8.20
48B−090(X) 7.20 − 8.20
36C−110 6.50 − 7.50
48C−110 6.90 − 7.90
60C−110(X) 6.50 − 7.50
48C−135 6.70 − 7.70
60D−135 6.70 − 7.70
60D−155 6.80 − 7.80
Page 28
TABLE 14
LP
2 cu ft 1 cu ft 2 cu ft
Dial Dial
164 205
110 136
82 102
66 82
54 68
46 58
LP−2500 btu/cu ft
TABLE 15
Range Nat CO Range LP
2 2
6.80 − 7.80
8.00 − 9.00
7.80 − 8.80
7.70 − 8.70
7.70 − 8.70
7.50 − 8.50
8.50 − 9.50
7.50 − 8.50
7.60 − 8.60
7.60 − 8.60
7.80 − 8.80
DIAL
410
272
204
164
136
116