The compressor forces refrigerant, in vapor form, into the condenser coil where it is cooled by ambient air. As it cools, the refrigerant condenses into a liquid, which is passed through a filter to remove impurities and excess moisture. The liquid refrigerant flow is metered by a thermostatic expansion valve (or capillary tube), to control its flow into the evaporator coil.
The liquid refrigerant enters the evaporator and begins to evaporate (vaporize) into a gas. As the hot air from the enclosure passes through the evaporator coil, the heat is transferred to the refrigerant, converting the refrigerant to vapor. High levels of humidity present in the air are removed by condensation; the water is drained to the outside or re-evaporated into the outside air. This cool, dehumidified air is then returned to the cabinet. After the heat is transferred to the refrigerant in the evaporator, the refrigerant passes into an accumulator, where any remaining liquid is separated. The gas then returns to the compressor to repeat the cycle in a continuous process.
Control of the system is generally kept simple. When power is applied to the air conditioner the evaporator blower (or fan) starts and runs continuously. If the temperature within the enclosure is high, the condenser blower and the compressor turn on, operating until the thermostat setting is reached. The thermostat is used as a low limit setting. This is typically 75ºF, the point at which the compressor and the condenser blower is turned off. Air within the enclosure continues to be circulated by the evaporator blower, picking up heat from the components within the cabinet. The thermostat has a differential setting that is typically 12-15 degrees above the low limit setting. When the air circulated within the enclosure rises by this amount (about 90ºF), the compressor and condenser blower turn back on, reducing the cabinet internal air temperature once again. Therefore, it would be normal at start up for the internal temperature to rise to this 90ºF temperature before the cooling process would begin. As the air cools, a balance of temperature within the enclosure is reached. Ideally the compressor and condenser blower continue to run most of the time until the heat load changes.
It is important to understand that enclosure cooling is not “comfort” cooling as found in homes and buildings. Heat producing power and control components are typically limited to maximum enclosure air temperatures of 100ºF to 110ºF. The actual component surface temperatures are higher. Maintaining enclosure temperatures at excessively low settings often becomes problematic. Condensation may form on live electrical surfaces if their temperature falls below the dew point of the air. Subsequent corrosion or electrical safety becomes a serious issue.
Air conditioners are required where the equipment operating temperature must be kept at or lower than the ambient room temperature, and/or the cabinet must be sealed from oil, dust, fumes and other contaminants.
Specially designed air conditioners protect the components and furnish the required cooling. Such air conditioners employ hermetic refrigeration systems with customized controls. They provide enclosure and air-path geometries for direct installation to the equipment cabinet and accomplish the following:

HEAT LOAD TRANSFER The amount of heat that is conducted through the exposed area of the enclosure from the warmer to the cooler space. Heat load transfer can be a heat gain, or a heat loss to the cabinet, depending on the conditions.
If the air outside the cabinet is warmer than the air inside the cabinet, the heat is moving through the cabinet and increasing the total heat load - this will require a larger capacity air conditioner.
If the air outside the cabinet is cooler than the air inside the cabinet, the heat is moving through the cabinet and decreasing the total heat load - this will require a smaller capacity air conditioner.

NEMA National Electrical Manufacturers Association - Your equipment may require a NEMA rating to comply with local codes. See page 9 for chart of NEMA Enclosure Ratings. Air conditioners typically carry an agency marking such as UL (Underwriters Laboratories), which designates the environmental hazard from which the contents are being protected. This marking should be matched to the enclosure to be cooled. Typical examples include NEMA 12, (indoor use, protection from dust and dripping liquids), NEMA 3R, (outdoor use and rain proof) and NEMA 4/X (outdoor or indoor use, protection from wash-down and corrosive environments). Depending upon the NEMA enclosure type, an air conditioner can be provided to operate in most locations. Locations subject to dust, dripping liquids, rain, washdown and corrosive atmospheres can utilize these “Special Purpose Air Conditioners.”

RADIO FREQUENCY INTERFERENCE (RFI) “Noise” that is accidentally generated by electrical products that interferes with the normal transmission and reception of radios and other equipment that uses radio waves.

RELATIVE HUMIDITY A unit of measure to describe the amount of water (moisture) in air. It is described in percent, i.e. %RH - over 80%RH is very humid, and below 30% is very dry. (See Condensation)

SOLAR LOAD or SUN LOAD The heat from the sun must be considered when identifying the total heat load on a system. This solar load can be minimized if the equipment cabinet is shielded from the direct rays of the sun. If this is not possible, painting the cabinet a light color and adding insulation should be considered. If none of these alternatives are possible, the capacity must be increased to address this additional heat load. In the southern USA, this affect can be significant. In the northern USA, this affect might be negligible.

STATIC PRESSURE A method used to quantify the air pressure created by a fan or blower wheel. Low static pressure exists at the outlet of a fan that is blowing into an open air space. High static pressure is created when the same fan is blowing into a restrictive, closed compartment. High static pressure is an indication of low airflow, and possibly poor cooling. If the components in a product are inherently very congested, the air flow through them will be restricted and create high static pressure. This condition can be overcome with an alternate blower wheel housing design. Typically a larger motor is needed to overcome this condition.

TEMPERATURE CONTROL Typical refrigeration and air conditioning systems control temperature by on/off compressor cycling as air temperatures fluctuate between minimum and maximum thermostat settings. Compressor start-up often introduces substantial transient noise into the circuit powering the equipment to be cooled. Thermostat or relay operation results in electromagnetic interference. Both of these factors can adversely affect the function of electronic equipment. On/off compressor control necessitates choosing between large temperature excursions or frequent compressor cycling.
Furthermore, frequent start/stop operation exposes internal compressor components to electrical and mechanical strains not encountered during continuous operation. The use of electrical controls to handle high compressor start-currents results in eventual erosion of the control contacts themselves.
In order to eliminate the possibility of these problems, KOOLTRONIC Air Conditioners feature a continuously operating compressor and non-electric proportional control system, which result in more stable equipment temperatures and prolonged life for the compressor and the control system. Both blowers and the compressor start simultaneously with the application of power to the unit, and continue to operate until power is removed at the time of equipment shutdown.
The Hot Gas Bypass Control Valve permits refrigerant to be injected into the evaporator coil. This high-temperature gas presents an artificial heat load and permits the effective cooling rate to be varied as necessary to maintain a constant return air temperature back to the enclosure. This control also prevents evaporator freeze-ups during periods of low heat load or low ambient temperature.
Although the above control system works effectively at most times, there are instances of over-cooling due to low heat load or low ambient temperature. In order to prevent that condition, Low Temperature Control thermostats and EMI/RFI suppressors have been added to all KOOLTRONIC Air Conditioners.
When activated, the Low Temperature Control shuts off the compressor and condenser (ambient side) blowers. The evaporator (enclosure side) blowers continue to circulate the air through the enclosure and air conditioner. When the air temperature again reaches the level at which cooling is needed, the compressor and condenser blowers resume operation.

UNDERWRITERS LABORATORIES, INC. (UL) The leading third party product safety organization in the United States, the largest in North America and the leading quality system registrar headquartered in the United States. Providing product safety verification services for more than a century, the UL Mark is one of the world’s most familiar safety certification symbols. The Canadian Standards Association (CSA) provides similar service in Canada. Recently UL and CSA have been working cooperatively and have adopted joint procedures, standards and marks.

WATT A unit of measure for electrical power. Watts are also used to quantify the amount of heat in a system, because 1 watt will convert to 3.413 BTU’s.