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E−Check Manifold Pressure
To correctly measure manifold prressure, the differential
pressure between the positive gas manifold and the nega-
tive burner box must be considered. Use pressure test
adapter kit (available as Lennox part 10L34) to assist in
measurement.
1 − Connect test gauge +" connection to manifold pres
sure tap on the gas vavle.
2 − Tee into the gas valve regulator vent hose and con-
nect test gauge −" connection.
3 − Start unit on low heat (40%) rate) and allow 5 min-
utes for unit to reach steady state.
4 − While waiting for the unit to stabilize, notice the
flame. Flame should be stable and should not lift from
burnere. Natural gas should burn blue.
5 − After allowing unit to stablize for 5 minutes, record
manifold pressure and compare to value given in table
42.
6 − Repeat stpes 3, 4 and 5 on high fire.
CAUTION
Do not attempt to make adjustments to the gas valve.
F− Proper Gas Flow (Approximate)
1 − Operate unit at least 15 minutes before checking gas
flow. Determine the time in seconds for one revolu-
tions of gas through the meter. A portable LP gas me-
ter (17Y44) is available for LP applications.
2 − Compare the number of seconds and the gas meter
size in table 39 to determine the gas flow rate. Multiply
the gas flow rate by the heating value to determine the
unit input rate. If manifold pressure is correct and the
unit input rate is incorrect, check gas orifices for proper
size and restriction.
3 − Remove temporary gas meter if installed.
NOTE − To obtain accurate reading, shut off all other gas
appliances connected to meter.
TABLE 39
Gas Flow Rate (Ft.
3
/Hr.)
Seconds for 1
Revolution
Gas Meter Size
1/2 cu ft Dial
1 cu ft Dial
10
180
360
12
150
300
14
129
257
16
113
225
18
100
200
20
90
180
22
82
164
24
75
150
26
69
138
28
64
129
30
60
120
32
56
113
34
53
106
36
50
100
38
47
95
40
45
90
42
43
86
44
41
82
46
39
78
48
38
75
50
36
72
52
35
69
54
33
67
56
32
64
58
31
62
60
30
60
G− 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. The maximum carbon
monoxide reading should not exceed 100 ppm.
TABLE 40
High Fire
Unit
CO
2
%
For Nat
CO
2
%
For L.P.
G71MPP−36B−070
6.8 − 7.8
8.5 − 9.5
G71MPP−36C−090
7.2 − 8.2
8.5 − 9.5
G71MPP−60C−090
7.2 − 8.2
7.2 − 8.2
G71MPP−60C−110
7.6 − 8.6
7.6 − 8.6
G71MPP−60D−135
7.5 − 8.5
7.5 − 8.5
TABLE 41
Low Fire
Unit
CO
2
%
For Nat
CO
2
%
For L.P.
G71MPP−36B−070
5.0 − 6.0
5.8 − 6.8
G71MPP−36C−090
4.9 − 5.9
5.7 − 6.7
G71MPP−60C−090
4.9 − 5.9
5.7 − 6.7
G71MPP−60C−110
5.0 − 6.0
6.2 − 7.2
G71MPP−60D−135
5.0 − 6.0
5.7 − 6.7