DeVilbiss DeVO/MC44-90 - Page 11

SECTION 5
ALARM SYSTEM
2.
Long Cycle: This light indicates a long
cycle time. When the pre-set maximum
cycle time is reached, this alarm will be
activated.
Possible Cause: A faulty compressor, leak,
or any problem that causes the maximum
pre-set cycle time to be exceeded.
NOTE: The long cycle light will come on
by itself when the maximum cycle time
has been exceeded. However, it will
come on with the high pressure light
when a high pressure situation exists in
the unit. Further testing must be done to
determine the exact cause of the
problem. Refer to the Service
Instructions, Section 7 for the proper
testing procedures for the compressor or
purge depending on which alarms come
on. See number 4 below: High Pressure.
No Cycle: This light indicates a failure of
the four-way valve to shift properly.
Possible Cause: Defective or sticking four-
way valve, inadequate pilot pressure,
faulty wiring from valve to MC board, or
defective MC board. A severe restriction
of flow or contaminated beds may also
activate this alarm.
NOTE: The short and no cycle lights will
come on together whether it is a four-
way or bed failure. Further testing must
be done to determine the exact cause of
the problem. Refer to the Service
Instructions, Section 7 for the proper
testing procedures for the four-way and
sieve beds.
High Pressure: This light indicates a high
pressure situation in the system.
Possible Cause: Purge valve remained in
the activated position due to a defective
MC board or sticking valve.
NOTE: The high pressure and long cycle
lights will come on together when a high
pressure situation exists in the unit.
Further testing must be done to
determine the exact cause of the
problem. Refer to the Service
instructions, Section 7 for the proper
testing procedures for the purge valve.
When any of the four red indicator lights
come on the compressor will
automatically shut off but the cooling fan
will continue to operate. Also, the
audible alarm will sound and the "Service
Required” light on the control panel will
illuminate.
The MC board also has two green indictor
lights (8 Fig. 12) labeled “purge” and
“four-way.” These are not alarm lights.
Purge: This green indicator light will
come on only when the purge valve is
activated (approximately 1.0 seconds).
Four-Way: This green indicator light will
come on only when the four-way valve is
activated. At the same time the right
sieve bed is being pressurized. When it is
off, the left bed is pressurizing.
Important: Instead of the alarm
designations explained in this section
(Short Cycle, Long Cycle, No Cycle, High
Pressure) some DeVO/MC44's may have
the following alarm light designations:
Bed, Purge/Compressor, 4-way, High
Pressure. These were used on the
DeVilbiss Models MC29 and DeVO/44. in
either case they refer to the same type of
malfunctions and should be used the
same way.
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