Automotive air conditioning leak repair

Written by chris stevenson
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Automotive air conditioning leak repair
Using an electronic leak detector can swiftly pinpoint a leak in your air conditioning system. (Jupiterimages/ Images)

If the air conditioning system in your car or small truck no longer blows cold air, a lack of Freon, or refrigerant, is the most likely prognosis. Vehicles routinely lose refrigerant at hose joints, through the pores of old or worn hoses, at coupler junctions and through bad seals. When the refrigerant level drops below a minimum level, not enough gas is processed through the air conditioning system and only cool or warm air blows through the vents. Several self-service repair options are available to fix some of the most common AC leak problems.

Skill level:

Things you need

  • Owner's repair manual
  • Electronic leak detector
  • AC hoses (if applicable)
  • AC gauges
  • AC recovery system
  • Socket set
  • Ratchet wrench
  • End wrenches

Show MoreHide


  1. 1

    Shift your vehicle into park or neutral and set the emergency brake. Raise the hood. Look for any oil-like substance on the AC hoses that feels sticky to the touch. Check both the low and high side hoses. Refer to your vehicle owner's manual for the location of these hoses. The low side hose typically will be marked with an "L" and the high side hose will be marked with an "H." Examine the suction hoses at the back of the compressor as well.

  2. 2

    Check the condenser fittings that attach to the small radiator device at the front of the vehicle for evidence of oil on the fittings. Inspect the hard line fittings that connect to the accumulator, the tall cylinder that attaches to the firewall. Inspect the service ports (also called Shrader valves) on the high and low side hoses. Unscrew the small Shrader valve caps and look for oil inside the valve openings.

  3. 3

    Start the vehicle and turn the air conditioning to maximum. Turn on a hand-held electronic leak detector.

  4. 4

    Hold the leak detector probe over each joint and hose coupler. If the detector beeps, it indicates a refrigerant leak. Use an end wrench to tighten that joint or coupler. Then, retest the joint or coupler with the leak detector. No beep indicates a proper seal. Use an end wrench to tighten all fittings that show oil or cause a beep signal on the detector. If the unit continues to beep after you've tightened a joint or coupler, go on to the next step.

  5. 5

    Shut off the engine and disconnect the negative battery cable. Hook up a set of AC gauges to the underside of the hood. Connect the blue gauge hose to the low-side Shrader valve on the AC hose and connect the red gauge hose to the high-side Shrader valve on the AC hose.

  6. 6

    Open the red and blue knobs on the AC gauges. If both needles register no pressure, it means you have lost all refrigerant in the system. You can replace a hose or fitting now, since the system is already depressurised. However, if the needles register any pressure, hook up the middle gauge hose (yellow) to a recovery system tank and open the valve on the recovery tank.

  7. 7

    Plug in the recovery system unit and turn it on. Let the recovery pump remove the refrigerant from the AC system, according to the directions. Once this is done, unhook the recovery machine. It is now safe to remove and replace any hard line or hose on your AC system.

  8. 8

    Remove damaged hoses or hard AC lines using the appropriate tool. For a hard line coupler joint with a double-nut fitting, use two end wrenches to loosen it -- one wrench to hold the inner line nut and the other to loosen and remove the outermost nut. Replace the hard line with the new replacement part, as needed.

  9. 9

    Use a socket to remove the bolt that holds each flange to the mounting surface to replace a low- or high-side hose. Be sure to replace the O-rings inside the fitting on end of the hose.

Tips and warnings

  • If you discover a leak on the underside of the compressor near the clutch assembly, it means the front seal has blown. In this case, removal and a complete rebuild of the compressor are necessary.
  • The condenser, which is the small radiator that sits in front of the cooling radiator, can suffer impact damage from rocks and other road debris. If the condenser suffers external damage, it must be removed and soldered to seal the structural leak.
  • Never loosen an AC hard line or hose in a pressurised system. Use a recovery unit to depressurise the AC lines and compressor before continuing with repairs.

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