How to Discharge an Automotive Air-Conditioner

by Craig WoodmanUpdated September 26, 2017

Most cars are equipped with air-conditioning systems to keep the passenger's compartment cool and comfortable. These systems also make a vehicle safer to operate, because they work with the vehicle's defroster to dehumidify the interior and prevent window fogging and icing. The near-universal presence of automotive air-conditioning presents a good business opportunity for repair facilities that wish to add on to their customer base and provide a valuable service. An investment in an air-conditioning service machine and obtaining an Environmental Protection Agency certification will have you servicing air-conditioners quickly using these steps.

Determine that the car's air-conditioning system contains pure refrigerant before discharging, or evacuating the system of refrigerant. Use a refrigerant purity indication tool for this task. This is an electronic tool that connects to the air conditioning service port and reads a small sample of refrigerant. Although most automotive refrigerant is pure, some facilities not qualified to work with air-conditioning may have added refrigerant a contaminated or even flammable system. Recover contaminated refrigerant in a separate container so that it is not re-used. Use a filter in your recovery equipment designed to separate sealers put in the system to stop leaks. These materials can damage recovery equipment.

Connect the air-conditioning recovery and recharge machine to the air-conditioning service ports. The low pressure side connector is indicated with a blue cap, and a red cap covers the high pressure side. The hoses on the machine are color-coded the same way. Connect the hoses to the corresponding ports. Note any pressure readings in the system on the recovery machine's gauges.

Start the evacuation process. Many air-conditioning service machines are automatic, and you just have to push one button or turn a knob. The pump inside of the machine will start, moving the refrigerant into the machine's internal tank. The pressure gauges will drop as the refrigerant is recovered.

Allow the air-conditioning service machine to draw the system down so that a vacuum exists, as shown on the gauges. When the gauges reach zero, the recovery process from the vehicle is complete, and there is no more refrigerant in the system.

Allow the system to hold a vacuum for at least 10 minutes. If the vehicle is unable to maintain a vacuum on the gauge, the air-conditioning system has a leak, which must be repaired before the system is recharged with refrigerant. Program the machine to dispense the amount of refrigerant required by the vehicle's system. This is usually indicated on a sticker under the hood. Start the charging process by setting the machine to start. When the process is finished, check the air-conditioner for correct function.

Items you will need

  • Air conditioning service machine

  • Refrigerant purity tool

  • Supply of HC-134A

  • EPA certification


If the air-conditioner is cold, but not as cold as it should be, you can add a small amount of refrigerant using cans sold at auto parts stores. Some of these cans also include a fluorescent dye, which will show up as a bright green color when illuminated by a special lamp. This helps show where the system is leaking.


Do not discharge the system by loosening a hose fitting or removing a hose. This is illegal, and refrigerant fumes can be harmful if inhaled. Do not service an air-conditioning system unless you are EPA certified to do so.

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