Lennox G21Q3-80, Информация об устройстве

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Page 47
B − External Static Pressure
1 − Measure tap locations as shown in figure 62.
FIGURE 62
EXTERNAL STATIC PRESSURE TEST
MANOMETER
G21 UNIT
GSR21 UNIT (HORIZONTAL)
GSR21 UNIT
2 − Punch a 1/4" diameter hole in supply and return air ple
nums. Insert manometer hose flush with inside edge of
hole or insulation. Seal around the hose with perma
gum. Connect the zero end of the manometer to the
discharge (supply) side of the system. On ducted sys
tems, connect the other end of manometer to the return
duct as above. For systems with non−ducted returns,
leave the other end of the manometer open to the at
mosphere.
3 − With only the blower motor running and a dry evapora
tor coil, observe manometer reading. Adjust blower
motor speed to deliver required amount of air.
4 − External static pressure drop must not be more than 0.5"
W.C on Q" units and 0.8" W.C on V" units.
5 − Seal around the hole when check is complete.
C − Manifold Pressure
Checks of manifold pressure are made as verification of
proper regulator adjustment. Manifold pressure for the
G21/GSR21 can be measured at any time the gas valve is
open and is supplying gas to the unit. Normal manifold
pressure is 2.0 + 0.2 in. W.C. for natural gas and 9.0 + 0.2
in. W.C. for L.P. gas.
To Measure Manifold Pressure:
1 − Remove 1/8" pipe plug from pressure tap on elbow be
low expansion tank. See figure 23 for location.
WARNING
For safety, connect a shutoff valve between the
manometer and the gas tap to shut off gas pres
sure to manometer if desired.
2 − Insert hose adapter in tap and connect gauge.
3 − Set thermostat for heating demand (the demand can
be started at the unit by jumping R" and W" on the
low voltage terminal strip).
BE SURE TO REMOVE THE JUMPER AFTER THE
TEST IS COMPLETE.
4 − Check the manifold pressure after the unit has ignited
and is operating normally.
5 − If the unit is not operational SEE CAUTIONS AND
WARNINGS BELOW. Check the manifold pressure
immediately after the gas valve fully opens.
6 − The gas valve can be adjusted using the regulator adjust
ment screw. This screw is located under the dust cover
screw on the face of the valve next to electrical terminals
and manual on/off knob. Refer to figure 24.
WARNING
Disconnect heating demand as soon as an accu
rate reading is obtained and allow unit to post
purge heat exchanger before proceeding.
DANGER
Combustion chamber access panel and air de
coupler box cover must be in place for this test. Do
not allow long periods of trial for ignition. Unsafe
conditions could result.
WARNING
If unit is not operational, a manifold pressure check
should be used only to verify that gas is flowing to
combustion chamber at correct manifold pressure.
Always allow purge blower to evacuate combus
tion chamber before proceeding.
D − Line Pressure
Gas supply pressure should not exceed 13.0 in. W.C. and
should not drop below 3.5 in. W.C. Normal natural gas level
for G21/GSR21 units is 7.0 in. W.C. and 11.0 in. W.C for L.P.
units. Supply pressure should only be checked with unit
running. A 1/8" pipe plug and tap are supplied in the elbow on
the inlet supply of the gas valve. Line pressure ratings are
listed on unit rating plate.
E − Flame Signal
Flame signal or microamp is an electrical current which
passes from the ignition control through the sensor electrode
during unit operation. Current passes from the sensor
through the flame to ground to complete a safety circuit. A 50
microamp DC meter is needed to check flame signal for GC1
equipped units. GC3 units require a digital meter and a trans
ducer (Part no. 78H5401).
In a standard gas furnace, flame sensing is measured in a
steady flame. A Pulse" furnace does not have a steady
flame to measure. Current can only be measured during
pulse cycles. Between cycles, no current can be mea
sured. Since the pulse rate approximates 60 pulses per
second, the flame sensor measures an electrical average
of the flame pulses.