How to Recharge Your Car's Air Conditioning

When an air conditioning system loses its ability to cool properly, it may be necessary to recharge the system with new refrigerant. Keep reading for a R-134a A/C pressure chart and steps on how to recharge the A/C system when the system is low on pressure or has been vacuumed out following a repair.

Note: Always wear safety glasses and gloves when charging the A/C system.

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DIY Car AC Recharge in 8 Easy Steps

1. Determine Ambient Air

If the temperature of the air is 55°F or below, do not charge the vehicle. It is also always recommended to use a charging hose with a gauge. The refrigerant packaging should contain a chart like the one below for determining what pressure to charge the system depending on the ambient air temperature. If no chart is provided, use the A/C pressure chart below this list as a general guide. Also, different AC systems can have different recommended pressures, so it’s worth taking a look in a repair manual or online to determine the right pressure for your vehicle. Following these guidelines when recharging the system will ensure the system can operate efficiently. It is important to note, charging an AC system with just a single gauge attached to the refrigerant is possible, but it is always recommended to use complete set of manifold gauges, which monitor both the high and low side pressures. These gauges are available for sale, and for rent at most AutoZone stores. At this point, start the vehicle and set the air conditioning to MAX setting. Locate the vehicle’s AC compressor for reference, and it’s important to monitor what the AC clutch is doing. When the AC compressor is disengaged, only the outside of the pulley will turn. When it’s engaged, the entire clutch assembly will turn, driving the compressor. Your compressor is designed to not engage at all when refrigerant pressures, or volume is too low.

2. Locate the Low-Side Service Port

This port is typically found on the line connecting the accumulator and compressor. The high side fitting is located between the AC compressor and condenser and is the larger of the two fittings. Consult the service manual to verify the exact location of the low-side service port. If hooking a can of refrigerant with a single hose/gauge to the car, you will use the low side. If hooking a set of gauges to the vehicle, you will use both.

*Most 1994 and older vehicles used R12 as the original refrigerant, if the vehicle being serviced is still using R12, it must be evacuated and retrofitted. Mixing R12 and any other refrigerant is illegal. Never use the high-side port to add refrigerant, doing so is very dangerous and could cause harm. You will notice an R12 style fitting right away as the hose screws on to attach and has the look of a tire valve, while an R134A fitting is a larger quick-connect. ALSO – starting in 2013, many vehicles began using 1234YF refrigerant. This refrigerant is NOT compatible with R134A, and should be left to the professional to troubleshoot.

3. Wipe Away Dust

Wipe away any dust with a clean rag and then remove the cap from low-side service port.

4. Attach the Charging Hose

Attach the charging hose to the low-side service port and ensure that you have a secure connection. If the hose does not attach easily you may be using the wrong port. Attach both connections if using a set of gauges.

5. Add Refrigerant

Following the instructions on the refrigerant package, add refrigerant to the system.

6. Charge the System

After determining the correct pressures using the ambient air pressure chart, monitor the pressure readings constantly while charging the system. If the system was low, your AC compressor clutch will not engage. You should notice that as the low-side pressure reaches approx. 25-30PSI, that the compressor clutch will engage. You may notice the compressor clutch engage and disengage as more refrigerant is added. Eventually, it should stay engaged all the time. It is absolutely important to note here that over-charging the system will cause permanent damage. If you are unsure of the current pressure, or amount of refrigerant in your system, you should seek a professional mechanic near you to address the issue.

7. Remove the Charging Hose

After the air conditioning system is charged to the proper pressure, remove the charging hose from the low-side service port, (or gauges) leaving the can attached to the charge hose, and store any additional refrigerant in a dry, cool spot.

8. Check the Service Port Cap Seal Before Reinstalling

Ensure that the seal beneath the cap does not have any cracks, nicks, or tears. This seal can be added protection if the Schrader valve ever formed a leak.

AC Pressure Chart

AC Temperature Pressure Chart for R-134a Recharging

After you’ve recharged your air conditioning, the difference should be noticeable immediately. It may be worth checking the pressure once or twice after recharging in case the low refrigerant level was caused by a leak in the system. If you believe there is a leak, get a UV light and some UV dye so you can find the leak. The UV dye will make the hole visible when the UV light is shined onto the A/C components.

Whatever you need to work on your auto air conditioning system, you can get it at AutoZone.

Do you need a more in-depth look into your vehicle to help you with your project? ALLDATA, the leading provider of automotive repair information, is now providing DIYers with the same information that the pros use with ALLDATAdiy’s single-vehicle subscriptions.

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Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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