Air Conditioner Recharge

These repair instructions give step by step instructions on how to recharge an automotive air conditioner.

Difficulty Scale: 4 of 10

This guide pertains to all vehicles.

Tools and Supplies Needed to Complete this Job

  • Air conditioner recharge gauge set or re-charge kit
  • 134a Refrigerant
  • Protective eyewear and gloves
Park your car on a level surface with the engine warm but not running. Apply the emergency brake and put the transmission in park. Completely Read Before Starting.

Step 1 - Start engine and adjust the AC system to "full cold" mode with vent set to the "mid" level. (Air flow should come out of the main vents in dash, also electric radiator fan should be ON if so equipped) After about 3 minutes of running the air temperature should be cold. If the air is warm (not cold) raise the hood of the car to check the AC compressor. With the engine still running the compressor clutch should be engaged. If the compressor clutch cycles on and off at idle or engine cruising speeds the system probably needs recharging. If the compressor is not engaged with the system set to the "on" position or, an AC system recharge is needed proceed to the next step. If the AC compressor is engaged and the air is not cold, locate the exhaust tube to the evaporator near the firewall. (There are two tubes headed to and from the evaporator, the exhaust tube is the larger of the two.) Once this tube has been located grasp the tube to determine the temperature of the tube. If the tube is cold but there is warm air being blow from the vents, troubleshooting and repair is needed. If the temperature of the low side tube is warm continue to the next step.

Step 2 - With the engine "off", locate the high and low pressure charge ports used to service the air conditioner system. The high pressure port is located on the liquid (small tube) part of the system. (Usually between the compressor and condenser.) The low side port or "charge port" is were the 134a is installed, this fitting is larger is size than the high pressure fitting. (Never charge the AC system through the high side port, this can cause the refrigerant container to receive high pressure which can cause a rupture.)

AC Compressor With High Pressure Port

Step 3 - Once the low side pressure port has been located remove the dust cap and attach the low side pressure hose (blue) and observe the gauge reading. Ambient outside temperature will cause static pressure to vary. As a general rule of thumb the gauge should read between 60 and 80 PSI. If ambient pressures are okay and the compressor is not engaging with the system "on", troubleshooting and repair is needed. If ambient pressure is okay, start the engine and turn the AC system to full cold with a high fan speed setting. The compressor should engage while the low side gauge readings decrease.

Step 4 - If the system requires a simple recharge and a "low side" charge kit is being used, while holding the can upside-down slowly open the valve to allow refrigerant to enter the system. (Caution: once 134a starts to flow stop opening the valve, do not open valve fully.) As the 134a enters the system the low side gauge will start to fluctuate, this is normal. As the system is charging grasp the outgoing evaporator line to monitor the temperature, the system is full when the line gets cold. (Caution: Once the outgoing evaporator tube gets cold stop filling the system to avoid overcharging.) (Note: Adding too much refrigerant will inhibited the systems operation.) Once AC system charge is complete, close the charge kit valve, and quickly remove the low side charge port fitting. (Note: Some discharge is normal). Before re installing the dust cap check the port valve for leakage.) After recharging the system check the inside vent air temperature to complete the recharge.


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2014-12-31)