Find Your Car's A/C Refrigerant or Air Conditioning Freon Leak

Low refrigerant (Freon, 134A) is the most common cause of A/C systems blowing warm air in automotive A/C systems. The refrigerant is used to transfer heat from the passenger compartment to the outside. Cars today hold considerably less refrigerant than cars in the past, so even small leaks can affect A/C performance in a short period of time. If low refrigerant is suspected, a 134a A/C gauge set can be used to verify this. The pressure with the A/C turned off should be approximately 80 PSI on the AC gauge set, depending on the ambient (outside) temperature.


  1. A visual inspection should be performed to check for dye and/or oil (some manufacturers put UV dye in A/C systems from the factory).
  2. Check all AC components including the AC compressor front seal & evaporator drain tube. If the refrigerant leak is not evident, verify that dye is in the system or add dye (one method is with a dye injector).
  3. You may then use an ultraviolet light (UV Light) also called a black light, to inspect all AC components.
  4. Dip a sponge on a bowl of liquid soap and run the sponge on the A/C tubes to find any leaks.
  5. Check the entire system with an electronic leak detector, the evaporator can be checked at the evaporator drain tube.
  6. After the repair has been made, hook up an AC vacuum pump, and let the system stay in a vacuum for at least fifteen minutes. Turn the vacuum pump off and watch the AC gauge to see if the vacuum holds. If a loss of vacuum is noted, this could indicate a large leak, possibly from an o-ring on a component that was just worked on.


  • After adding oil to the system near or in the compressor, turn the compressor by hand ten revolutions to prevent damage to the compressor (oil cannot be compressed).


  • Wear safety glasses
  • Do not over-charge the system, damage to the compressor can occur.
  • Do not charge refrigerant into the high side.

Things You'll Need

  • AC Gauge Set
  • Electronic Refrigerant Leak Detector
  • UV Light

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