High And Low Pressure Controls

High And Low Pressure Controls

Both high and low pressure controls are recommended for good system desing on all air cooled systems 1 HP and larger, and are essential on all field installed air cooled systems and on all water cooled systems.

When used for low temperature unit operation control,  the low pressure control must not be set below the minimum operating limits of the compressor or the system.  One of the most frequent causes of motor overheating and inadequate lubrication is operation of the compressor at axcessively low suction pressures. Copeland specification sheets list the approved compressor operating range, and recommended minimum low pressure control settings for various operating ranges are shown in table 21.

High pressure controls may be either manual or automatic reset as desired by the customer. If of the manual reset type,  provision must be made to prevent liquid refrigerant flooding through the system to the compressor in the event of a trip of the high pressure control. 

Internal automatic reset pressure relief valves (copelimit)  are provided in most copelaweld compressors 1 1/3 HP and large. On factory assembled package systems, the internal copelimit valve may satisfy U. L. and code requirements without the use of an external high pressure control.  A similar high side to low side automatic reset pressure relief valve is installed in all copelametic compressors with displacements of 3,000 CFH or greater.

On factory assembled and charged package systems,  such as room air conditioner,  where loss of charge proection is not considered critical,  or where the motor protection device can provide loss of charhe prote tion, low pressure controls may not be essential although recommended.