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3
THEORY OF OPERATION
3.1
Micro 60U24 Control
STANDBY
The Micro 60U24 circuit control continually checks
for internal faults, safety circuit integrity and relay
contact positioning.
STARTING CIRCUIT
Upon a call for heat, the control will verify that the
burner and exhaust safety pressure switches are in
their proper position. The fan relay energizes the fan,
an operational static pressure is achieved and the
normally open burner switch will close, initiating the
ignition sequence. The glo-bar is powered and after
45 seconds the main gas valve opens.
FIRST STAGE RUNNING CIRCUIT
After ignition, the flame-rod monitors the main
burner flame. If flame is lost, the control acts to close
the gas valve within one second and a new trial
sequence identical to the start-up is initiated. If proof
is not established within 8.5 seconds, the unit will
retry 2 times and proceed to a hard lock-out. The
control can be reset by interrupting the power source
or thermostat.
SECOND STAGE RUNNING CIRCUIT
Stage two on the gas valve is powered directly from
the second stage of the thermostat. The gas valve will
not pass gas unless the first stage sequence of
operation has been completed. The thermostat will
determine which stage is required to maintain the
.
desired comfort level
SHUTDOWN
When the thermostat is satisfied the fan will enter
into a two minute post-purge cycle.
LOCKOUT CODES
In event of a component failure, a red LED
diagnostic light located on the burner box end panel
will flash a code identifying the fault. Lockout codes
are summarized below
LED STATUS
Initial flash on
power up, then
steady off
Steady On
1 Flash
2 Flashes
3 Flashes
4 Flashes
No flash upon initial
117 V power up
Figure 3.1.1
27
.
FAULT CODE
Normal Operation
Module Failure/
Internal Fault
Ignition Fault
APS1 Fault
APS2 Fault
Solenoid Valve Fault/
Leaky Valve/
Flame amplifier Fault
Transformer Fault
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