MN801GAS 060520
– 18 –
7 Adjust the burner using test instruments
(continued)
Step 3
Set butterfly gas valve linkage
1.
Switch the low-fire hold switch to low fire.
2.
Check CO
2
and CO. The CO
2
should be between 9.0% and 10.0% (natural
gas) or between 10.0% and 11.2% (propane); with CO less than 100 PPM.
3.
To adjust the low-fire air (change CO
2
), move the burner fuel selector
switch to OFF. Adjust the butterfly gas valve linkage as described in
the following to change the low-fire gas flow to the burner head. Do not
change the main gas pressure regulator setting.
4.
DO NOT ADJUST THE LOW-FIRE AIR DAMPER SETTING.
5.
See Figure 13 for location of linkage components.
Figure 13
Butterfly gas valve linkage
To adjust the linkage, loosen set screw in the adjustable link in
small increments. A 1/8-inch move can cause CO
2
to change
as much as 1.5%.
•
If more gas is needed (to increase CO
2
), slide linkage UP.
•
If less gas is needed (to decrease CO
2,
), slide linkage DOWN.
6.
Tighten the set screw in the adjustable link.
7.
The butterfly valve indicator must be at 90°. IF NOT, turn the burner
off. Loosen the two hex-head screws securing the valve linkage arm.
Rotate the butterfly valve indicator until it is at 90°. Disengage actuator
motor. Rotate linkage to high fire. Tighten the two hex head screws while
still holding the motor linkage arm in high fire. Rotate linkage to low fire.
Re-engage pin.
8.
Tighten the two hex head screws on the butterfly valve linkage arm boss.
9.
Restart and repeat as necessary until CO
2
and CO are acceptable.
IF EQUIPPED WITH LOW-HIGH GAS PRESSURE SWITCH,
PROCEED TO STEP 3A.
OTHERWISE PROCEED TO STEP 4
FOR MASS CODE, PROCEED TO STEP 3A,
OTHERWISE PROCEED TO STEP 4.
Step 2
Set main gas pressure regulator
The butterfly gas valve is factory set to a preliminary setting of
30% open for low fire, and 100% open for high fire. The pilot
regulator is set for 3.0 inches w.c. Use manometer inthe pilot
test port (Figure 12A) provided to confirm settings.
1.
Leave the low-fire switch in low fire.
2.
With the gas pilot operating correctly, and the UV sensor flame signal
above minimum required, the primary control will cycle the burner to
main gas.
3.
Check the flame signal after the pilot has shut down to ensure the signal
is still strong with main flame on.
4.
Move the burner fuel selector switch to OFF. The burner will shut down.
5.
Temporarily install two U-tube manometer connections to check gas pres-
sures. Install connections at the inlet pressure tap of the main manual
gas valve and at the downstream pressure tap of the manual gas valve
next to the butterfly valve.
6.
The gas pressure at the inlet to the gas train must never exceed
14 inches w.c., either when the burner is off or firing on gas.
7.
Move the burner fuel selector switch to GAS. The burner should start.
8.
With the burner firing in low fire, check the gas pressure at the downstream
manual gas valve tapping. Adjust the main gas pressure regulator if neces-
sary until the gas pressure reads 3.4 inches w.c. as a starting pressure.
9.
Switch the low-fire switch to high fire.
CAUTION
: Be prepared to turn the
burner off immediately if it begins to pulsate as it attempts to move to
high fire.
10.
If the flame pulsates, it is probably too rich. Switch the low-fire switch to
low fire and reduce the gas pressure by adjusting the main gas pressure
regulator. Then return to 9, above.
11.
If the fire is too lean, it will appear small and can even blow out during the
swing to high fire. If it blows out, shut off the burner immediately. Switch
the low-fire switch to low fire and start the burner again. Adjust the main
gas pressure regulator to increase the gas pressure. Return to 9, above.
With the burner running in high fire, inspect the buttefly valve
shaft slot (Figure 13). The slot must be horizontal. IF NOT, turn
the burner off. Loosen the two hex-head screws securing the
valve linkage arm. With the damper motor linkage arm pulled
up, use a screwdriver to rotate the butterfly valve slot until it is
horizontal. Tighten the two hex head screws while still holding
the damper motor linkage arm up. Return to step 9, above. DO
NOT proceed with combustion adjustment unless the butterfly
valve position has been verified, and corrected if necessary.
12.
With the burner running in high fire, adjust the main gas pressure regulator
to achieve the values in Table 6. Measure the CO content. It should be
no greater than 100 PPM.
High CO readings may indicate the combustion is on the wrong
side of the CO
2
curve. You will know this if a decrease in gas
pressure causes an increase in CO
2
.
13.
The gas pressure may have to be set as low as about 2.0 inches w.c. to as
high as about 4.0 inches w.c., depending on the firing rate of the burner.
Hex
Nuts
Set
Screw
Butterfly
Valve
Indicator
(red needle)
