A.O. Smith VB/VW-500 - Manual (Page 31)

31
ADJUSTMENT
There must be sufficient load to operate the boiler at high fire to
perform the following adjustments. Start the boiler and observe
proper operating parameters for the system.
Required Tools:
TORX
® T40 or 5mm hex wrench
3mm or 7/64in hex wrench
Combustion analyzer
The VF 500, 750, and 1000 boilers are equipped with a Honeywell
combined gas/air control and gas safety shut off control valves. The valve
functions in parallel with the variable speed combustion blower to supply
the correct gas air ratio for optimum performance and efficiency. The
combustion blower speed is controlled automatically and determines the
amount of negative pressure experienced by the gas safety shut off/control
valves. The gas/air regulator adjusts gas flow to maintain the proper
pressure at the outlet nozzle of the associated valve.
SETTING OF THE TEST MODE
On UIM go to main menu, scroll down to user settings and press
select. Scroll down to MOD mode, press select. Use the up and down
keys to select options: MIN (MINIMUM FIRING RATE). MAX
(MAXIMUM FIRING RATE). MOD (FOR AUTOMATIC MODULATION
MODE). Press select for the desired option. For checking the
combustion setup on MIN or MAX the boiler will remain in this state
for ten minutes before defaulting to the MOD (modulation) mode.
HIGH FIRE SETTING
NATURAL GAS 8.5 - 9.0% CO
2
PROPANE 9.5 - 10.5% CO
2
Set boiler to the “Test Mode High,” as described above, to
achieve maximum firing rate of the boiler. Check combustion
readings using a combustion analyzer. If combustion readings
are not in accordance with the chart above adjust as follows:
remove the flat, round, blue plastic cap from the cover. Using
a 3mm (7/64”) hex wrench, turn the adjustment screw
counterclockwise to increase or clockwise to decrease gas
flow and achieve the desired CO
2
level. See Table referenced
above for correct settings. There will be a slight time delay
between the adjustment and the response of the CO
2
measuring instrument. Adjust the settings in small increments
and allow the combustion readings to stabilize before
readjusting. When desired adjustments are complete, reinstall
the blue plastic cap on the cover. Combustion samples shall
be taken within two feet of the boiler. IMPROPER
ADJUSTMENT CAN CAUSE INCOMPLETE COMBUSTION
RESULTING IN DEATH.
LOW FIRE SETTING
NATURAL 6.5 - 7.5%
PROPANE 7.5 - 8.5%
Set boiler to the “Test Mode Low,” as described above, to
achieve minimum firing rate of the boiler. Check combustion
readings using a combustion analyzer. If combustion readings
are not in accordance with the chart shown above adjust as
follows: remove the cap on the gas regulator using a slotted
screwdriver. This will expose the offset adjustment screw.
Using a TORX
® T40 or a 5mm hex wrench, carefully adjust
the low fire gas setting to achieve the CO
2
level prescribed
in above reference table. Note: The rotation of the Low
Fire adjustment is opposite of the High Fire as follows:
Clockwise rotation increases gas flow, counterclockwise
rotation decreases gas flow.
Adjustments to the offset pressure regulators should not exceed
1/4 turn at a time before allowing the readings to respond and
stabilize.
After proper low fire offset adjustment is made, reinstall the slotted
cap on the regulator.
Following all gas valve adjustments, check for proper light-off and
verify correct fuel/air mix and combustion quality throughout the
entire firing range (from lowest to highest fan speed).
CONTROL SYSTEM
The EMC modulation control system is a fully integrated, state of
the art electronic control system. It consists of sensors, output
devices, a power switch, a 24VAC transformer, wiring, and the
following printed circuit boards:
•
Modulation Control Board (MCB), see Figure 2.
• Power Distribution Board (PDB), see Figure 2.
• User Interface Module (UIM), see Figure 19.
The MCB contains circuitry for both master control and flame
control. Dip switches on the MCB are used to configure the system.
The User Interface Module (UIM) communicates with the user
through a set of touch pads and a 4-line, 20-character LCD display.
The PDB provides connection points for input power, the water
pump, and the transformer. It also distributes power to the system
and contains the system fuses.
The MCB also contains an external communications
system to allow for connection to a PC, a modem, an EMS
system, or something similar. Through this connection,
multiple boilers can also be linked together. CAUTION:
The internal communications cables should never be
connected to the external communications connectors,
and vice-versa.
There are several microcontrollers used on the boards.
These control the temperature and ignition control functions
for the boiler. Inherent in the design are the normal
operating sequences and safety features associated with a
gas ignition control system. The system continuously
performs various diagnostic tests to verify proper appliance
and control operation. Should an unsafe condition occur, the
control will shut down the burner and display a red service
light as well as indicate the cause of the error on the display.
The operating programs for the system are stored in
permanent memory inside the microcontrollers. User-
selectable operating parameters and a history of detected
faults are stored in rewritable memory in the
microcontrollers. A loss of power does not affect either of the
memories.