Lennox International Inc Gas Units, G61MP Series Units Gas Pressure Adjustment

12−	If the appliance will not operate, follow the instructions
	urning Off Gas to Unit" and call your service techni-
	cian or gas supplier.
Turning Off Gas to Unit
1 −	Set the thermostat to the lowest setting.
2 −	Turn off all electrical power to the unit if service is to be
	performed.
3 −	Remove the upper access panel.
4 −	White Rodgers 36E Gas Valve − Move gas valve
	switch to OFF.
	Honeywell VR8205 Gas Valve − Move switch on gas
	valve clockwise	to OFF. Do not force.
5 −	Replace the upper access panel.

Gas Pressure Adjustment

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 12 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.

Supply Pressure Measurement

A threaded plug on the inlet side of the gas valve provides access to the supply pressure tap. Remove the threaded plug, install a field−provided barbed fitting and connect a manometer to measure supply pressure. Replace the threaded plug after measurements have been taken.

Manifold Pressure Measurement

To correctly measure manifold pressure, 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 − Remove the threaded plug from the outlet side of the gas valve and install a field−provided barbed fitting. Connect test gauge

measure manifold pressure.

2 − Tee into the gas valve regulator vent hose and connect test gauge

TABLE 12

Gas Flow Rate (Ft.3/Hr.)

Seconds for 1	Gas Meter Size
Revolution	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

3 − Start unit on low heat (68% rate) 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 13.

6 − Repeat steps 3, 4 and 5 on high heat.

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.

CAUTION

Do not attempt to make adjustments to the gas valve.

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