Troubleshooting guide

PV500-17 07/13 Section 17
11
MAXIM
AXIAL FLOW GAS BURNER START-UP (continued)
This section pertains to MEC120 control only.
When the blower motor starts, the air proving
light on the MEC120 should be on. This
indicates a positive airflow condition. If the air
proving light is not on, turn air proving switch
adjustment screw counter-clockwise until the
air proving light comes on, then turn screw one
turn counter-clockwise. If the gas valves open
and close intermittently during normal
operation, turn screw one half turn counter-
clockwise until this condition ceases. This
procedure should be followed with every
burner.
After purging is complete, terminal 3 energizes
the pilot valve and terminal 4 energizes the
ignition transformer on the control. The pilot is
then established. The VDC reading on the
meter should read a steady 14-17 VDC. Each
different control will have the required flame
response signal stamped on it. This is the
minimum for it to properly operate. If the pilot
fails to light during the initial period, it is
probably due to air in the line. The control will
lock out. Wait one minute and push the flame
safeguard reset button to restart burner and
begin the purge cycle again.
Once the flame is established, set the pilot
pressure (measured downstream of gas valve)
at pressure shown on the tag attached to gas
train. Next, open the main gas valve slowly.
Set manifold pressure at pressure shown on
the tag attached to gas train. Do not screw the
adjusting nut of the regulator in past the point
where no further increase in manifold pressure
is noted. Check the incoming pressure with the
burner running. This is recorded as inlet flow
pressure.
Our standard flow pressure requirement on
these burners is 8" W.C. flow. If the required
manifold cannot be reached, check the inlet
pressure. It should be a minimum of that
shown on the heater decal with the burner
running on full input. It is important that the
incoming pressure does not fall below these
minimums or nuisance control lockouts could
occur.
IMPORTANT
Where low gas pressure is a problem, special
arrangements may have been made to fire the
burner with reduced pressure. The appliance
data decal will reflect this information.
17. Direct Spark Ignition - (DSI) Burners - No
pilot. (See wiring diagram.)
Connect manometer to the manifold test port.
Set the air shutter as shown on the tag
attached to gas train. This may not be the
exact setting you end up with, but it is a good
starting point.
Turn the unit on, using the rocker switch on the
side of the control enclosure assembly. The
burner should come on and ignition occur. If
the burner fails to ignite, there may have been
air in the line. To reset the control, turn the
switch off for 60 seconds (S89 controls only)
and it should automatically reset, or push the
reset button on the control. If after the
appropriate prepurge, ignition does not occur,
turn air proving switch adjustment screw
counter-clockwise until TFI (try for ignition)
occurs. Now in order to more precisely adjust
the air failure set point, slowly turn screw
clockwise until the burner shuts off. Then turn
screw counter-clockwise one turn. If the gas
valves open and close intermittently during
normal operation, turn screw one half turn
counter-clockwise until this condition ceases.
Once the burner fires, set manifold pressure at
pressure shown on the tag attached to gas
train. There will be a tap on the downstream
side of the valve to measure pressure. The
manifold pressure must be taken downstream
of the gas valve. Check the incoming pressure
with the burner running. This recorded flow
pressure must be the minimum specified on
the heater decal.