AIRTAK C-25 Instructions d'installation, d'utilisation et d'entretien - Page 6

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3. Evaporator: Water-to-Refrigerant Heat Exchanger:
The evaporator is constructed of high quality copper tubing. Cold liquid refrigerant is efficiently fed by a
venturi type distributor to each circuit. The circuiting within the evaporator is designed to insure
adequate refrigerant velocity to eliminate the problem of oil return to the crankcase.

4. Expansion Valves:

There are two types of expansion valves used.
a) The first type is the automatic type which is used on all AIR/TAK chillers up to, and including, the
Model C-75. The Automatic Expansion Valve (AEV) is a pressure sensitive valve which
responds to change in evaporator pressure. As the evaporator pressure begins to change in
response to load changes, the automatic valve senses this and adjusts the flow of refrigerant to
maintain a constant pressure within the evaporator.
b) The second type is the Thermostatic Expansion Valve (TXV) used on Model C-100 and larger.
This valve is controlled primarily by temperature. The temperature that is sensed by the (TXV)
thermal bulb is the superheat temperature of the refrigerant at the outlet of the evaporator. This
is the temperature increase of the refrigerant above the saturation temperature corresponding to
the existing evaporator pressures.

5. Hot Gas Bypass Valve C-100 and Larger:

The hot gas bypass valve or capacity regulator permits medium to larger type refrigerated chillers to
operate through the range from zero load to 100% load while maintaining evaporator and suction line
pressure and temperature.

6. Low Pressure Switch:

The low pressure switch is a safety device that protects the refrigeration compressor from low suction
pressure resulting from a loss of refrigerant charge.

7. High Pressure Switch:

The high pressure switch is a safety device that limits the discharge pressure from the refrigerant
compressor. If the discharge pressure exceeds the factory set point, the high pressure switch opens the
electrical circuit to the compressor and the system is shut down.
High discharge pressures may result from conditions such as: plugged or dirty condensers, high ambient
temperature, high fluid inlet temperatures, high fluid flow rates, non-condensables (air or water inside the
refrigeration system) or fan motor failures.

8. Crankcase Heater:

The crankcase heater is a low wattage heater that is connected to or immersed in the refrigerant
compressor crankcase. The wattage of this heater is normally 50 to 65 watts. This heater is not
controlled by the operational switch of the chiller, but is factory wired directly to the incoming power. The
purpose of the crankcase heater is to prevent liquid refrigerant migration back to the crankcase while the
compressor is not in operation. This migration of the liquid refrigerant occurs when the compressor
crankcase is at a lower vapor pressure than the evaporator and other system components. The
crankcase heater must raise the temperature of the crankcase and oil to a temperature higher than the
evaporator and all of the interconnecting piping. To accomplish this, the crankcase heater must be
energized twenty-four hours before the chiller is started. This is accomplished by turning the chiller
operational switch to "OFF" and switching on the main power. The chiller is then allowed to warm up for
twenty-four hours after which time the operational switch may be turned to the "ON" position.
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