DeVilbiss DeVO/MC44-90 - Capacitor; Cooling Fan; Microcomputer Control Board

SECTION 7
SERVICE INSTRUCTIONS
objects to come in contact with the terminals
on the capacitor.
To replace capacitor:
1. Unplug unit from wall outlet.
2. Refer to Service Instruction B to open
cabinet covers.
3. Disconnect the two wires from terminals
on the capacitor.
4. Cut the two nylon cable ties holding
capacitor in place and remove capacitor.
5. Install new capacitor and secure with
cable ties.
Reconnect wires to capacitor terminals.
Replace cabinet covers and secure with
cabinet fasteners.
. Cooling Fan
The cooling fan (12 Fig. 11) provides a
constant air flow for the compressor. A
defective cooling fan will cause the com-
pressor to overheat and automatically shut
off.
To replace cooling fan:
1. Unplug unit from wal! outlet.
2. Refer to Service Instruction B to open
front cover.
3. Disconnect the cooling fan quick-connect
terminal.
4. Remove the four retaining screws (11 Fig.
11) that secure the fan to the vertical
divider.
5. Remove the defective fan and secure the
replacement fan in position with the four
retaining screws.
NOTE: When installing the fan, be sure the air
flow directional arrow on the side of the fan
is directed toward compressor.
6. Reconnect the quick-connect terminal.
7. Replace the front cover and secure with
cabinet fasteners.
Microcomputer Control Board
The microcomputer control board or MC
board (7 Fig. 12) located on the inside of the
front cover is responsible for monitoring and
controlling the DeVO/MC44. It activates all
alarms and maintains the normal pressure/
depressurization cycle. When a system
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malfunction is sensed by the MC board, the
alarm system is activated. Depending on the
type of failure, a visible alarm on the unit
control panel will illuminate and the red
indicator lights (8 Fig. 12) on the MC board
will come on. The audible alarm will also
sound.
A pressure transducer (13 Fig. 12) on the MC
board constantly senses oxygen pressure in
the accumulator tank. This transducer is
connected to the accumulator tank by a 1/16”
(1.6 mm) diameter hose (14 Fig. 12) and senses
the rise and fall of pressure within the
accumulator throughout each cycle. Once the
accumulator pressure reaches approximately
25.5 PSI (176 KPa) the MC board sends a signal
(approximately 12-15 VDC) to the four-way
and purge valves, activating them and
starting a new cycle. Until accumulator
pressure reaches 25.5 PS! (176 KPa) the valves
will not shift. Normally it takes approximately
16 seconds at 2 LPM for a bed to pressurize
and complete the cycle, but factors such as
altitude and flow rate will affect this cycle
time. Increases in altitude and/or flow rate
will increase cycle time slightly. Decreases will
cause an opposite effect.
A minimum and maximum cycle time has also
been pre-set on the MC board. if the unit
cycle time does not remain within these limits,
the alarm system will be activated. If the unit
cycle
time exceeds the pre-set maximum cycle
time, the long cycle alarm light will come on.
When the pre-set minimum cycle time is
reached the short and no cycle alarm lights
will come on. See Section 5, Alarm System.
To replace MC board:
Unplug unit from wall outlet.
2. Refer to Service Instruction B to open
front cover.
3. Disconnect the terminal connectors at
end of wire harness (12 Fig. 12) from the
MC board by pulling them straight out.
4. Remove the 1/16" hose attached to the
transducer (14 Fig. 12).
5. Remove the four screws (6 Fig. 12) that
secure the board to the cabinet and
remove the MC board.
6. Install the new MC board and secure it
using the four screws.
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