Glossary of terms

By Jim VanderGiessen Jr, Pro Refrigeration Inc.

BTU – British Thermal Unit. In scientific terms, it represents the amount of energy required to raise one pound of water one degree Fahrenheit. One BTU is the equivalent of the heat given off by a single wooden kitchen match. For your home, it represents the measure of heat given off when fuel is burned for heating or the measure of heat extracted from your home for cooling. Capacity – The output or producing capability of a piece of cooling or heating equipment. Cooling and heating capacity are normally referred to in BTUs.

Compressor – The heart of a refrigeration system. It is part of the unit that pumps refrigerant. The compressor maintains adequate pressure to cause refrigerant to flow in sufficient quantities in order to meet the cooling requirements of the system.

Condenser coil – The coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid.

Evaporator – In the evaporator, refrigerant evaporates and absorbs heat from the glycol as it crosses over the coil.

Heat exchanger – A device for the transfer of heat energy from the source to the conveying medium. HVAC – Heating, ventilation and air conditioning.

Packaged system – A piece of refrigeration equipment in which all components are located in one cabinet. Used occasionally in residential applications, the packaged unit is installed either beside or on top of the home.

Refrigerant – A substance that produces a refrigerating effect while expanding or vaporizing.

Refrigerant lines – Set of two copper lines connecting the outdoor unit and the indoor unit.

Thermostat – A temperature control device. It consists of a series of sensors and relays that monitor and control the functions of a refrigeration system.

Ton – A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.


Main Electrical Disconnect Disconnects switch provides fused and non-fused protection of the chiller system. If customer decides not to purchase this option, most local electrical codes will require one installed in the field.

System Function Switches The function switches allow easy shut-down of all or part of chiller system.

Complete system fusing All components should be protected with either fuses or circuit breakers.

System Function Indicator Lights The indicator lights are beneficial for trouble shooting and preventive maintenance programs.

System Alarm Indication Lights In the event of a safety control alarm, an indicator light will alert you to the source of the fault and decrease costly downtime.

Electronic Temperature Control Temperature controllers range from one stage up to eight stages. Electronic controls have proven to be more accurate and reliable than the “cap-tube” controllers that have been used in the past.

Digital Glycol Temperature Display The LED displays your process glycol temperature. Typically will also provide a digital set-point display for better control of your chiller out-put.

HIGH PRESSURE CONTROL A high pressure control will shut the compressor off in the event of a high condensing pressure situation. The main cause of a high pressure condition is a fouled water cooled condenser, lack of water being supplied to condenser, dirty or blocked air cooled condenser, or non-condensables with-in the system. In the event of a high pressure condition please contact a certified refrigeration mechanic or contact the factory.

LOW PRESSURE CONTROL The low pressure control will shut the compressor off when the suction pressure drops to a pre-set point. This will occur when your thermostat has satisfied and closed the liquid line solenoid valve. This control will also turn the compressor on when the solenoid valve is opened by the thermostat. The compressor will turn on when the suction pressure rises to the low pressure cut-in point on the control.

LOW PRESSURE FREEZE PROTECTION The low pressure freeze control is a low pressure safety switch. If suction pressure falls below a pre-set point, the control will energize a time delay relay. If the suction pressure does not rise above the pre-set point with-in the 60 second time delay, the control will close the solenoid valve. This control must be manually reset, it will not reset until suction pressure has risen above the pre-set point. An alarm indicator light on the control panel will alert you to such a problem. Reasons why the suction pressure would drop and this control would operate, could be caused by a freeze situation in the evaporator barrel or a system operating with a low refrigerant charge.

OIL FAILURE CONTROL This control is only used on semi-hermetic reciprocating compressors. The controller senses the refrigerant oil pressure of the oil pump discharge and determines that it is higher than the suction pressure of the compressor. An oil failure could be due to; failed oil pump, a refrigerant leak and loss of oil, or liquid refrigerant flooding back to compressor and “washing” the oil out of the crankcase. An alarm indicator light will alert you to this. If an oil failure occurs, a certified refrigeration mechanic should be called to check the system. Do not repeatedly re-set the oil failure control, the compressor will undoubtedly fail.

FAN CYCLE CONTROL In order to maintain condensing pressure levels during low ambient conditions, a fan cycling control is used. As the condensing pressure drops, the fan cycle control will break the circuit to a condenser fan motor. As the condensing pressure rises the control will close the control circuit to the fan motor and cause it to come on.

COMPRESSOR UNLOADING VALVES The Unloader valve uses an electric solenoid valve to by-pass a portion of the discharge gas into the suction chamber. Since both the suction and discharge pressures on the unloaded cylinder are approximately the same, the piston and cylinder do no work other than pumping vapor through the by-pass circuit. This prevents compressor from cycling off and on during fluctuating load conditions. A compressor supplied with an Unloader valve will always start in an unloaded stage, lowering the starting amps. A customer will see increased energy efficiency on a chiller system with compressor unloading. The Unloader valve is controlled by the electronic thermostat.

Jim VanderGiessen Jr. is CEO and general manager of Pro Refrigeration Inc., Auburn, WA., a 17 Year Company specializing in manufacturing Glycol Chiller System for numerous Food and Beverage Markets.