MAXIM

AXIAL FLOW GAS BURNER START-UP (continued)

This section pertains to MC120 control only.

When the blower motor starts, the air proving light on the MC-120 should be on. This indicates a positive air flow 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 counterclockwise 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.

NOTE: 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.

16.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.

PV500-17 05-2000

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Section 17