Carrier 69NT40-511-199, 69NT40-521 manual Refrigeration Circuit with Receiver

2.7 REFRIGERATION CIRCUIT WITH RECEIVER

Starting at the compressor, the suction gas is compressed to a higher temperature and pressure.

When operating with the air-cooled condenser, the gas flows through the discharge service valve into the pressure regulator valve that is normally open. The pressure regulator valve restricts the flow of refrigerant to maintain a minimum discharge pressure of 5 kg/cm@ (70 psig). Refrigerant gas then moves into the air-cooled condenser. Air flowing across the coil fins and tubes cools the gas to saturation temperature. By removing latent heat, the gas condenses to a high pressure/high temperature liquid and flows to the receiver which stores the additional charge necessary for low temperature operation.

From the receiver, the liquid refrigerant continues through the manual liquid line valve, the filter-drier (which keeps refrigerant clean and dry), and a heat exchanger that increases subcooling of liquid refrigerant to the thermostatic expansion valve. As the liquid refrigerant passes through the orifice of the expansion valve, some of it vaporizes into a gas (flash gas). Heat is absorbed from the return air by the balance of the liquid, causing it to vaporize in the evaporator coil. The vapor then flows through the suction modulation valve (and suction solenoid valve under some conditions) to the compressor.

The thermostatic expansion valve bulb on the suction line near the evaporator coil outlet controls the thermostatic expansion valve, maintaining a constant

superheat at the coil outlet regardless of load conditions, except at abnormally high container temperatures such as during pulldown (valve at maximum operating pressure condition).

NOTE

A pressure control system has been incorporated by means of a condenser pressure transducer (CPT) and condenser pressure control (CPC) logic to maintain discharge pressures above 130 psig in low ambients.

Regardless of pressure, CPC will be disabled at every compressor start-up, 15 seconds before the compressor is energized and 30 seconds after. An exception, for two-speed compressor units, is the low speed to high speed switching sequence, where CPC will be disabled while SMV is at 0% during the entire switching sequence for a total of 47 seconds.

a.At ambients below 27_C (80_F), the condenser fan will cycle on/off depending on condenser pressure and on/off times.

1.The condenser fan will start if the condenser pressure is greater than 200 psig OR the condenser fan is OFF for more than 60 seconds.

2.The condenser fan will stop if the condenser pressure is less than 130 psig AND the condenser fan remains ON for at least 30 seconds.

b. At ambients above 27_C (80_F), condenser pressure control (CPC) is disabled and the condenser fan runs continuously.

T-268-07 2-14