Operation; Sequence Of Operations - Modine Manufacturing MRS Series Installation And Service Manual

MRS Series
4.0

Operation

Sequence of Operation
Standby: The ignition module (circuit board) continually checks for internal faults, circuit integrity, and relay
contact positioning.
Starting Circuit: Upon a call for heat, the control verifies that the burner and exhaust pressure switches are
in their proper positions. The control energizes the fan. Once operational static pressure is achieved,
the burner pressure switch will close and the exhaust pressure switch remains closed 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.
Low Fire 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.
High Fire Running Circuit: The second stage on the gas valve is powered directly from the second stage of
the thermostat. In order for high fire to engage, low fire must be energized as well. The thermostat
determines which stage to maintain for the desired temperature.
Shut Down: When the thermostat is satisfied, the fan will enter a two (2) minute post-purge cycle.
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Operation • Sequence of Operation