Research Project Information

Research Project Summary Information

Visual Refrigerant Charge Fault Detector for Optimum Performance of Residential HVAC Systems (ST10929-1)

Steven Winter Associates, Inc.


Faulty operation of HVAC systems, including air-conditioners and heat pumps in residential buildings is prevalent and results in increased energy use. Correct refrigerant charge is very important for proper operation of an air-conditioner or heat pump. According to EPA’s Energy Star website, “recent field studies suggest 75% of installed cooling equipment may have the incorrect amount of refrigerant. Incorrect refrigerant level can lower efficiency 5-to-20% and can cause premature component failure”. An overcharged unit can cause the refrigerant to flood back to the compressor crankcase. This dilutes the compressor oil and can result in oil bearing damage/failure. An undercharged unit will provide less than rated capacity while consuming more energy. In addition, the compressor can overheat due to insufficient refrigerant returning to the compressor. Both conditions reduce efficiency, but undercharge will result in a higher loss.

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Project Description

Development of a low cost, stand alone, easy to use device that detects an air conditioner refrigerant overcharge and under charge condition. Under this project, Steven Winter Associates 1) evaluated different techniques to determine refrigerant subcooling could be used to characterize refrigerant charge fault, 2)performed field tests to establish the envelope for normal/abnormal charge, and 3) built and tested a pre-prototype charge fault detector in the field. The project also includes Steven Winter Associates developing a product commercialization strategy.


There are more than eight million households in New York State. About 1.1 million residential units (single family homes) have central air-conditioning that consumes two billion kWh/year. Assuming 50% of these homes have systems refrigerant that is over or under charged and 10% of the energy is wasted, it is estimated that detection and correction of the under and over refrigerant charge can save 100 million kWh. The cost of this energy waste is $16 million ($0.16/kWh). The correct level of refrigerant in an AC system avoids premature component failure, saving consumers costly repairs. A low cost, stand alone, easy to use device that detects an air conditioner refrigerant overcharge and under charge condition would enable HVAC technicians and homeowners to diagnose and correct the problem.

Project Results

Project sucessfully developed and demonstrated (with one field multi-day test) a digital prototype for detecting refrigerant charge faults. A digital, differential temperature measurement and control device with two temperature sensors to sense subcooling directly was determined an ideal candidate based on cost effectiveness, simplicity and reliable performance. Data obtained from the field test results was compared against previously analyzed laboratory data, obtained from National Institute of Standards Testing (NIST), and compared favorably to indicate accuracy of charge condition(s). Detection and visual display of fault conditions was demonstrated via the prototype. Cost of the device and implementing it into appropriate trade organizations is an open issue that needs further pursuit.


Steven Winter Associates, Inc.
61 Washington St
Norwalk, CT 06854

Principle Investigator

Srikanth Puttagunta

Universities Involved


Project Type:

Product Development

Technologies Types:

Building Systems
Heating, Ventilation, & Air Conditioning
Cooling & Ventilation

NYSERDA Contact Information

Gregory Pedrick


R&D -Transport & Power Systems

Contract Details

Start Date: 1/11/2010
Project Status: Active
Contract Number: ST10929-1

Last Updated: 4/17/2012