62-11039 4-16
4.7.2 Unloader Control Overrides
With the complex control systems in use with the
Advance Microprocessor, there are many different
reasons -- other than the number of degrees the box
temperature is away from setpoint -- that the
compressor unloaders may be operating loaded or
unloaded This section lists the different factors that
determine the operation (loading and unloading) of the
unloaders.
Unloaders operate in priority order for cool mode ONLY:
The overrides will be allowed in default mode if the
override does not use the return or supply temperature.
There is always a minimum delay of 20 seconds
between LOADING and UNLOADING cylinders under
all operating conditions except when the engine is
starting.
When the Compressor is Off the Unloaders are always
de--energized.
1. LOW GENERATOR AMP DRAW
When alarm A128 “LOW AC AMPS” is active, the
compressor will only operate on 2 or 4 cylinders.
2. HIGH GENERATOR AMP DRAW
When the compressor is operating and either one or
both of the unloaders is energized (unloaded), they will
not be allowed to de--energize whenever the
compressor discharge pressure is above 415 psig (28.2
Bar) OR when the compressor Amp draw is more than
25 Amps when operating in diesel engine mode or more
than 21 Amps when in standby.
3. FAN MOTOR DELAY
When ever any fan motor has been energized, there
will bea3seconddelaybeforeeitherunloader is
allowed to de--energize.
4. 2--MINUTE DELAY
If the compressor is on and an unloader isenergized
due to a refrigeration system pressure (override
overrides # 4, 7, 8, or 9), the unloader remains
energized for 2 minutes.
5. COMPRESSOR STARTUP
• UL1 remains energized (unloaded) for a minimum
of 10 seconds when the ambient is above 100°F
(37.8°C) or 5 seconds when the ambient is at or below
100°F (37.8°C) after Compressor Motor Contactor is
energized.
• UL2 remains energized (unloaded) for a minimum
of 60 seconds when the ambient is above 100°F
(37.8°C) or 30 seconds when the ambient is at or below
100°F (37.8°C) (ambient is greater than 37.8°C) after
Compressor Motor Contactor is energized
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