Sequence Of Operation - Modine MDB Série Manuel D'installation Et De Maintenance

start-uP Procedure

sequence of operation

remote switch in "off" Position
With the Summer/Off/Winter switch in the "Off" position, the unit
is shut down and neither the blower nor the burner will operate.
remote switch in "summer" Position
With the remote switch in the "Summer" position, the following
sequence of operation will occur.
note: If freeze protection is furnished with the unit, the freeze
protection timer will be energized at this time to provide power
to the inlet and/or discharge damper motor (if furnished with
unit).
1. The inlet and/or discharge air damper motor is energized.
2. When the damper is fully open, the internal damper motor
end switch will make and allow power to be supplied to the
blower motor or blower motor starter.
3. The gas controls and temperature controls are locked out to
prevent heating during the "Summer" mode of operation.
remote switch in "Winter" Position
With the remote switch in the "Winter" position, the following
sequence of operation will occur.
note: If freeze protection is furnished with the unit, the freeze
protection timer will be energized at this time to provide power
to the inlet and/or discharge damper motor (if furnished with
unit).
1. The inlet and/or discharge air damper motor is energized.
2. When the damper is fully open, the internal damper motor
end switch will make and allow power to be supplied to the
blower motor or blower motor starter.
3. Air flow pressure switch proves (closes) and allows power
to be supplied to the flame safeguard sequence enabling
circuit. Power is supplied through the normally closed high
temperature limit(s) control contact. (Blower light is lit if
supplied)
4. After 10 seconds of pre-purge time, the flame safeguard
ignition sequence is energized, the pilot ignitor is energized,
the pilot valve is opened, and the pilot is lit. (If the following
optional controls are supplied, the power to the flame
safeguard is routed through the high and/or low gas pressure
switch(s), mild temperature inlet On/Off stat, motorized proof
of closure valve, and timed freeze protection relay.)
5. After the pilot is lit and proved, the main gas valves are
energized and the burner fires at low fire. The main valve
"on" light is lit.
6. Burner remains on low fire momentarily, then the
temperature controls take over and fire the burner based on
load demands.
note: If the unit has been supplied with a dirty filter switch,
the filter light will come on only if the pressure drop across the
filters becomes excessive.
If a flame failure should occur, the flame failure alarm light
on the remote panel will light. The flame safeguard relay will
go into the lockout mode. The flame safeguard must be reset
manually in order to restart the unit (reset button is located in
the electrical cabinet of the unit). Before resetting, a service
person must inspect the unit, determine the cause, and take
corrective action.
24
Figure 24.1 - typical remote control Panel
(Shipped separately for mounting by others)
7-500.10