Check Manifold Pressure; Proper Gas Flow; Proper Combustion - Lennox G71MPP SERIES Unit Information

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.
Seconds for 1
Revolution
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
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.
Unit
G71MPP−36B−070
G71MPP−36C−090
G71MPP−60C−090
G71MPP−60C−110
G71MPP−60D−135
Unit
G71MPP−36B−070
G71MPP−36C−090
G71MPP−60C−090
G71MPP−60C−110
G71MPP−60D−135
Page 49
TABLE 39
3
Gas Flow Rate (Ft. /Hr.)
Gas Meter Size
1/2 cu ft Dial
180
150
129
113
100
90
82
75
69
64
60
56
53
50
47
45
43
41
39
38
36
35
33
32
31
30
TABLE 40
High Fire
CO %
2 For Nat
6.8 − 7.8
7.2 − 8.2
7.2 − 8.2
7.6 − 8.6
7.5 − 8.5
TABLE 41
Low Fire
CO %
2 For Nat
5.0 − 6.0
4.9 − 5.9
4.9 − 5.9
5.0 − 6.0
5.0 − 6.0
1 cu ft Dial
360
300
257
225
200
180
164
150
138
129
120
113
106
100
95
90
86
82
78
75
72
69
67
64
62
60
CO %
2 For L.P.
8.5 − 9.5
8.5 − 9.5
7.2 − 8.2
7.6 − 8.6
7.5 − 8.5
CO %
2 For L.P.
5.8 − 6.8
5.7 − 6.7
5.7 − 6.7
6.2 − 7.2
5.7 − 6.7