Because of the effect of temperature on the volume of the gaseous refrigerant used to charge or recharge an air conditioning system, ambient outdoor temperature is a factor during a maintenance call. Gas administered into the system on too cold a day may over expand on a warm day creating a system freeze. Since only a professional with an EPA Refrigerant Usage Certification can only legally administer refrigerant, be sure to ask what method the technician intends to use during a recharge.
How AC Systems Work
A central air conditioning system is a closed loop that has several components. Starting outside the home in the compressor, refrigerant is changed from gas to a cold liquid and sent into the evaporator inside the home. Warm air is cooled in the evaporator and sent to the house via the ducts. The refrigerant absorbs the warmth from the house and returns to the compressor to start the cycle again. At no time in this process is refrigerant burned up or vented. Over time, however, leaks can evolve requiring maintenance and recharge.
How AC is Recharged
Because of its ozone-depleting qualities, refrigerant can never be vented to the atmosphere and can only be handled by trained and certified professionals. Refrigerant is administered into the compressor as a gas via high-pressure lines with precise fittings to reduce the chance of any gas escaping. Prior to a recharge, a technician will attempt to determine how much refrigerant is in the system.
Most air conditioning service technicians will not charge an AC system when outdoor temperatures are lower than 55 degrees Fahrenheit. This is because of the expanding nature of gas when heated. Refrigerant loaded in cold weather will expand and possibly create an inefficient situation. Ideally, outdoor temperatures will be warm. There are no high-temperature issues for charging or recharging on hot days as the gas will enter the system and fully expand. While the gasses loaded on hot days will contract on cold days, the reduction in volume will not pose a problem. It is never advisable to run air conditioning in cold temperatures because of reduced refrigerant volume.
Cold Weather Charging
The only method considered acceptable for sub outdoor 55 degree Fahrenheit temperatures is the weigh-in method. Manufacturers post the system's refrigerant weight on the compressor unit. The number is listed in pounds and ounces and will give the technician an estimate of the gas needed to fill the system. If the system is being loaded for the first time, the technician will calculate the volume of the line and evaporator and with reasonable accuracy. It is advisable not to have your system recharged – or topped off -- on a cold day because the process will involve too much guesswork. Regardless of an initial charge or recharge, once outdoor temperatures have returned to above 55 degrees, the technician should return to confirm that the system charge is suitable.
Beer Can Cold
Beer can cold refers to an inaccurate way to charge the system by adding refrigerant until the suction line becomes as cold as a chilled can of beer. Since this is a relative term and has no actual temperature, it is not only inaccurate, it can cause freezing in the system from an overload of refrigerant and is not recommended.
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