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ADJUSTMENT OF ENGINE GAS PRESSURE
The gas pressure leaving the White-Rodgers 25M gas valve
should be preset at 5" W.C. with engine speed at 1200 rpm.
Lower gas pressure here will cause engine stalls under high
load conditions.
PRESSURE REGULATOR
UNDER COVER SCREW
FIGURE 13 - WHITE-RODGERS 25M GAS VALVE
It is normal to see lower pressures at higher engine rpm. Refer
to Figure 13 for outlet pressure tap location. No adjustments
are necessary to the gas engine regulator valve.
CHECKING AND ADJUSTING OXYGEN (O
LEVEL ON ENGINE
NOTE: CARB units installed in California cannot have
the mixture screw adjusted. The following procedures
do not apply to these units.
The engine is factory set to 5.6 to 5.8% O
quality, altitude and building load may require an adjustment of
the gas mixture to achieve the proper setting in the field. Most
YORK distributors have an O
the instrument can be purchased through a YORK distributor.
The analyzer kit (Part Number 526-34457-000) includes the
UEI combustion analyzer, sampling assembly and a case.
If another analyzer is to be used, be sure to follow the proper
procedures to insure an accurate reading. A sampling assem-
bly can be fabricated out of two 12" lengths of 3/4" heater hose,
a tee,clamps and a smaller hose to connect to the probe of the
analyzer. The probe should be inserted so that it samples
engine exhaust perpendicular to the exhaust flow and is not
influenced by exhaust gas velocity or outside air.
Allow the system to run at high speed (SP17) for ten minutes
to stablize the system. Running in cooling mode and under
FIGURE 14 - O
ANALYZER CONNECTION
2
Unitary Products Group
OUTLET
PRESSURE
TAP
OUTLET
)
2
. However, gas
2
analyzer available to borrow or
2
medium load is preferred, but this is not practical most of the
time. Calibrate the analyzer and verify that it is operating
correctly (refer to analyzer instructions). The sensors wear out
quickly and can be ordered through a YORK distirbutor. The part
number is 526-34454-000 and the tee part number is 526-34456-
000. Connect the analyzer to the smaller hose and tighten clamp
to minimize leakage (connections are shown in Figure 14).
Press the run button or operate the sampling procedure of the
O2 analyzer. Allow the analyzer to run until the pump stops or
the reading stablizes. Record and repeat the sampling proce-
dure. Compare number to see if analyzer is reading properly.
If not, take a couple more samples. If this doesn't correct the
problem, inspect the analyzer to see if the sensor needs to be
replaced. The proper O
setting is 5.6 to 5.8%. To decrease the
2
% O
, turn carburetor mixture screw clockwise and to increase
2
turn the screw counter clockwise. The adjustment screw setting
is sensitive and the screw should not be turned more than 1/4
turn without taking an O
reading. It is good practice to calibrate
2
the analyzer after 4 or 5 samples have been taken.
FIGURE 15 - CONTROLS SEQUENCE (W/FURNACE)
515.35-N6Y
9
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