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AG2
Series
4.0
Operation
Sequence of Operation
Standby: The MICRO 60U-24 CONTROL continually checks for internal faults, circuit integrity and relay
contact positioning.
Starting Circuit: Upon a call for heat, the control verifies that the differential switch is in the proper
position (open). The control energizes the fan. Once operational static pressure is achieved, the
differential switch will close initiating the ignition sequence. The glo-bar is powered and the gas
valve opens after 45 seconds. If the flame is not sensed, the heater will attempt to re-ignite for a total
of three (3) trials for ignition before proceeding to soft lockout.
Single Stage Running Circuit: After ignition, the flame rod monitors burner flame. If sense of flame is
lost, the control closes the gas valve within one second and a new trial sequence (identical to the
starting sequence) is initiated. If flame sense is not established within 8.5 seconds, the heater will
attempt two (2) additional ignition sequences before proceeding to soft lockout. The control can be
reset by briefly interrupting the power source.
Two Stage Running Circuit: The second stage on the gas valve is powered directly from the second
stage of the thermostat. In order for two stage to flow to a higher output, single stage must be
energized as well. The thermostat determines which stage to maintain for the desired comfort level.
Shut Down: When the thermostat is satisfied, the fan will enter a two (2) minute post-purge cycle. ; soft &
hard lockout.
Thermostat
NOTE: Different thermostats operate according to their particular features. Refer to thermostat
specifications for details.
AG2 Series heaters require a 24V, two-stage thermostat to operate. The burner control box is equipped
with either a round terminal strip that accepts three (3) 1/4-inch insulated female spade terminals or a
36-inch yellow 24VAC control wire. Do not supply 120VAC to the 24VAC connection.
The AG2 Series is equipped with or without a relay board (P/N: HLRB).
Standard Configuration
Without relay board (white terminal label*):
• Single burner control box.
• Single thermostat.
Optional Configuration
With relay board (orange terminal label*):
• Required when a single thermostat controls two or more burner control boxes or when heaters are
common vented.
NOTE: Units with a relay board installed must have an external transformer (field supplied), see wiring
diagram. (Figure 2.1B) Stainless steel heaters, with a relay board, are indicated with the suffix 'D' on
the heater's rating plate.
*A yellow control wire replaces the external terminal plug on stainless steel models or models with water
resistant upgrades.
4.0
Operation
•
Operating Instructions
(must be factory installed)
•
Sequence of Operation
47
•
Thermostat
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