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5.5.9 Suction Pressure Operation
5.6
Component Replacement, Charge, Evacuation, & Leak Instructions
Note that a new liquid line filter dryer will be required any time a refrigeration system is opened for
servicing. New dryer should be of the same capacity as the original or larger.
Recovery
When there has not been a major refrigeration system leak, the system will contain refrigerant. This
refrigerant must be either recovered to separate cylinders appropriate for the refrigerant type or
isolated in a portion of the refrigeration system that will not be open for service. In all cases you
must comply with Section 608 Refrigerant Recycling Rule of the Clean Air Act.
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Desert Aire - SP Manual
Supply Air Temperature Set Point. The heater output will modulate to maintain the calculated
Supply Air Temperature Set Point. The heating mode is always disabled if the zone exceeds
the Zone Temperature Set Point. Resetting the supply air temperature in heating not only
closely maintains the zone temperatures, but helps ensure the supply air temperature is held
to minimum values. The default values used for the zone PID, supply air PID, and deadband
are appropriate for most applications and heater sizes. Should the command for Supply
Air Temperature change too quickly, the PID action for the reset can be slowed by increasing
the tuning values. Should the heater not be able to closely maintain the calculated Supply Air
Temperature Set Point, the values for the heater output loop can be adjusted.
Heater Enabled = Zone = Zone Set Point = Heating Deadband
Heater Disabled = Heat Output PID Loop < 5% or Zone = Zone Set Point
Example:
-
Zone Set Point:
-
Heating Deadband:
In this example, the binary heater contact will close at 83°F and the analog output
will start to increase. The PID loop will modulate to maintain the zone at the 83°F
temperature. Should the analog signal for heat decrease to less than 5%, the binary
contact will open. In addition, if the zone is sensed at greater than 85°F at any point,
the contact will open, limiting heater overshoot due to poorly tuned loop.
The low suction pressure alarm and trip protects the SP unit. Whenever the suction
pressure in either circuit falls below 58 psig, the unit compressors will shut off with an alarm
indication. The compressors will be allowed to restart when the suction pressure rises to
above 106 psig. Note that the compressors will be off for at least 5 minutes on the recycle
timer.
If the low suction pressure cycle occurs 3 (adjustable) times in a 1 (adjustable) hour time
period, then an alarm will be indicated and recorded in the alarm history as a multiple suction
pressure alarm.
85°F
2°F
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