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A/C Cooling Loss Caused by Numerous Factors

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snowflakeIt may be hard to think about A/C refrigerant this time of year, but when warmer weather arrives, the demand for refrigerant always jumps.

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Refrigerant is the working gas inside an A/C system. Refrigerants are gases that condense and change to a liquid at a certain temperature and pressure. They are normally a gas at room temperature and pressure. Compressing and cooling the refrigerant causes it to turn from a gas into a liquid. As long as the refrigerant is held under pressure, it remains in the liquid state. But as soon as the pressure is relieved, it immediately evaporates and turns back into a gas — absorbing heat in the process that produces a chilling effect.

In an automotive A/C system, the refrigerant travels in a continuous loop. The belt-driven compressor compresses the refrigerant to several hundred pounds per square inch. The high-pressure hot gas then flows into the “condenser,” which is a heat exchanger mounted in front of the radiator. Air flowing through the condenser cools the refrigerant and causes it to condense into a liquid. The high-pressure liquid then flows through a pipe or hose to the “orifice tube.” This is a metering device that has a small hose through which the refrigerant passes as it enters the “evaporator” (located inside the HVAC unit under the dash). As the refrigerant enters the evaporator, it expands, absorbs heat and cools the air flowing through the evaporator into the passenger compartment. The refrigerant (now gas) is then sucked back through a hose or pipe to the compressor to begin its journey over again.

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A lot of things can cause a loss of cooling in an A/C system, but obviously loss of refrigerant is one of the most common. Leaks anywhere in the system can allow the gas to escape, reducing the A/C system’s ability to blow cold air. Common leak points include the compressor shaft seal, hose and pipe connections, or pinholes in the condenser or evaporator. Leaks can be found with ultraviolet leak detection dye or an electronic leak detector. Leaky components must be repaired before the A/C system is recharged with more refrigerant otherwise it will just leak out as before. Federal law also requires any residual refrigerant that is still inside the A/C system to be recovered before the system is opened to replace parts. This is something professional technicians are aware of but most DIYers are not.

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Equally important is hooking up a vacuum pump to evacuate air and moisture from the A/C system after parts have been replaced. If this is not done, residual air will displace refrigerant reducing the cooling capacity and performance of the system. Residual moisture can form acids and sludge that can cause additional part failures. Again, this is something professional technicians should know but many DIYers do not.

Since 1995-1996, all vehicles have used R-134a refrigerant. R-134a can be purchased by professionals or DIYers, but pros must be certified to buy it in bulk containers. Pros also are required to have the proper refrigerant recovery/recycling equipment to service customer’s vehicles.

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Alternative refrigerants are available for older vehicles that use R-12 refrigerant. Alternative refrigerants are for older R-12 systems only (if R-12 is unavailable) and must not be used in R-134a applications. Older R-12 A/C systems can often be retrofitted to R-134a, which usually only requires changing the compressor lubricant from mineral oil to PAG or POE oil (on some vehicles, o-rings and seals may also have to be changed).

Lately, a new more environmentally friendly refrigerant called R-1234yf has been introduced in a handful of vehicles, and will eventually replace R-134a. These newer applications with R-1234yf should only use R-1234yf, never R-134a or other alternative refrigerants.

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