Lennox G27M Series Unit Information

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On multiple unit ins tallations , eac h unit should be
check ed separately,with and without other units oper-
ating. Supply press ure must be a minimum of 5.0
W.C. for eac h unit but no more than 13.0W.C. at any
time.
E--Check Ma nifold Pressure
After line pressure has been checked and adjusted,
check manifold pressure. Move pressure gauge to out-
let pressure tap located on unit gas valve (GV1).Checks
of manifold pressure are made as verification of proper
regulator adjustment. Manifold pressure for the G27M
can be measured at any time the gas valve is open and is
supp lying gas to the unit. Nor mal manifo ld pres sur e
for na tural gas uni ts is 3.5 W. C. ( 870.2 P a) f or hi gh
fire o perati on and 1.7 W.C. (422.7 P a) for lo w fi re.
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.
Thegasvalveisfac torysetandshoul dnotrequiread-
jus tment. All g as va lves are f acto ry regu lated.
Manifold Pressure Check Procedure:
1 -- Connect manometer to outlet pressure tap on gas
valve (see figure 17 for outlet tap location). 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.
3 -- After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to the normal
manifold pressure of 3.5 W.C. (870.2 Pa) for high
fire operation or 1.7 W.C. (422.7 Pa) for low fire.
NOTE--Shut unit off, turn gas valve to OFF position
and remove manometer as soon as an accurate
reading has been obtained. Take care to replace
pressure tap plug.
FIGURE 17
HIGH FIRE
MANIFOLD
PRESSURE
ADJUSTMENT
MANIFOLD
PRESSURE
OUTLET
WHITE RODGERS 36E SERIES GAS VALVE
F-- Proper Gas Flow (Approximate)
Furnace should operate at l east 5 minutes before
check ing gas flow. Determine time in sec onds for two
revolutionsofgasthroughthemeter. (Tworevolutions
assures a more ac c urate time.) Divide by two and
compare to time in table 7 below. Seconds in table 7
arebasedona1cu.ft.dialandgasvalue of 1000 btus
for natural and 2500 btus for LP. Adjust manifold pres-
sure on gas valve to match time needed.
NOTE-- To obtain accurate reading, shut off all other
gas appliances connected to meter.
TABLE 7
Unit
Seconds for
Natural
Seconds for
Propane
G27M2--60 60 150
G27M3--75 48 120
G27M4--100 36 90
G27M5--120 30 75
G--High Altitude Derate
Refer to table 8 for high fire manifold pressure settings
for installations at different altitudes. For low fire, no
manifold pressure adjustment is required.
TABLE 8
Manifold Absolute Pressure (Outlet) in. w.c.
UNIT
Altitude ---- feet (m) above sea level
UNIT
MODEL
0--2000
(0--610)
2000--4500
(610--1372)
4500--5500
(1372--1676)
5500--6500
(1676--1981)
6500--7500
(1981--2286)
G27M2--60
G27M3--75
G27M 4--100
G27M 5--120
3.5
(0.87)
3.5 (0.87)* 3.4 (0.85) 3.3 (0.82) 3.1 (0.77)
*No adjustment required.
NOTE -- In Canada, certification for installations at
elevations over 4500 feet (1372m) is the jurisdiction of
local authorities.
The combustion air pressure switches are factory set
and are not to be adjusted.
Factory-installed pressure switches are acceptable for
units installed at elevations up to 4500 feet (1372m).
Installations at higher elevations require replacement
of the high-fire pressure switch. Table 9 outlines pres-
sure switch requirements.
TABLE 9
UNIT MODEL
PRESSURE SWITCH
PART NUMBER
G27M2--60A--1 80K4001
G27M3--75A--1 80K4301
G27M4--100A--1 18L2501
G27M5--120A--1 18L2501
IMPORTANT
For safety, shut un it off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.

Lennox G27M Series Specifications

General

Brand	Lennox
Model	G27M Series
Category	Furnace
Language	English