Testing Gas Supply Pressure; Check Manifold Pressure; Proper Gas Flow (Approximate); Gas Meter Clocking Chart - Lennox G61MPV Service Manual

D−Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to
inlet pressure tap on the gas valve. See figures and 44 and
45. Check gas line pressure with unit firing at maximum
rate. Low pressure may result in erratic operation or under-
fire. High pressure can result in permanent damage to gas
valve or overfire. See table 36 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 table 36.
TABLE 36
All G61MPV Units
Line Pressure WC"
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 G61MPV can be mea-
sured at any time the gas valve is open and is supplying gas
to the unit. See table 40 for manifold pressures.
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 sensing atmo-
spheric pressure.
Manifold Pressure Measurement & Adjustment
NOTE − Pressure test adapter kit (10L34) is available from
Lennox to facilitate manifold pressure measurement.
1 − Connect test gauge to outlet tap on gas valve.
2 − Disconnect pressure sensing hose from gas valve and
plug hose using tape or equivalent. Leave hose barb
on valve open.
3 − Start unit on low heat and allow 5 minutes 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 burner.
Natural gas should burn blue.
5 − After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
40.
6 − Repeat steps 3, 4 and 5 on high heat.
Natural LP
4.5 − 10.5 11.0 − 13.0
Page 63
NOTE − Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to replace
pressure tap plug.
NOTE − During this test procedure, the unit will be overfir-
ing:
Operate unit only long enough to obtain accurate read-
D
ing to prevent overheating heat exchanger.
Attempts to clock gas meter during this procedure will
D
be inaccurate. Measure gas flow rate only during nor-
mal unit operation.
7 − When test is complete remove obstruction from hose
and return hose to gas valve barbed fitting.
F− Proper Gas Flow (Approximate)
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 37 below. If manifold pressure matches table 36
and rate is incorrect, check gas orifices for proper size and
restriction.
NOTE− To obtain accurate reading, shut off all other gas
appliances connected to meter.
TABLE 37

GAS METER CLOCKING CHART

Seconds for One Revolution
Natural
G61MPV G61MPV
Unit
1 cu ft
Dial
−45 82
−70, −071 55
−90, −091 41
−110, −111 33
−135 27
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.
G− Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com-
bustion. See sections E− and F−. Take combustion sample
beyond the flue outlet and compare to the following tables.
The maximum carbon monoxide reading should not ex-
ceed 100 ppm.
LP
2 cu ft 1 cu ft 2 cu ft
Dial Dial DIAL
164 205 410
110 136 272
82 102 204
66 82 164
54 68 136
LP−2500 btu/cu ft