How to Recharge Your Car's Air Conditioner

Car Interior, Air conditioning button
Kiyoshi Hijiki / Getty Images
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Before You Get Started

If your car uses R134 type refrigerant, you can recharge your own AC system.
Matt Wright

Before you set out to recharge your car's air conditioning system, you'll need to find out what kind of refrigerant it uses. The best way to determine this is to check your car's owners manual, or you can consult your repair manual.

If your car was manufactured after 1994, it uses R134 refrigerant. Older cars use R12 refrigerant, which is no longer manufactured. To get the AC working on a pre-1994 vehicle, you'll first have to it to a repair shop and have it converted to use R134.

You should also check your AC system for leaks before getting started. A leaky air conditioning system can't cool as efficiently; running it without sufficient coolant could cause permanent (and costly) damage.

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Buying Refrigerant

An R134 recharge kit includes a pressurized can of refrigerant and a pressure gauge.
Matt Wright

To recharge your air conditioning system you'll need pressurized refrigerant (sometimes referred to as freon) and a pressure gauge to keep track of how much is in the system. There are lots of different AC recharge tools you can buy, but most are for professional mechanics and are pretty expensive.

If your air conditioning maintenance is limited to the family cars, an all-in-one AC recharge kit is perfectly sufficient. These kits consist of a can of R134 and a pressure gauge built in. They work well and are very easy to understand, even for somebody who has no experience with AC. You can purchase AC recharge kits at your local auto store.

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Preparing the Recharge Kit

Turn the gauge counterclockwise to retract the pin that pierces the can.
Matt Wright

As you unpack your kit, you'll find a can of refrigerant, a flexible rubber hose, and a pressure gauge. Follow the instructions in the package to assemble the pressure gauge part of the kit. Usually, you'll have the hose already attached to the gauge. Before you screw the gauge into the can of refrigerant, be sure to turn the gauge counterclockwise until it stops. There is a pin inside the assembly that pierces the can of refrigerant once everything is together tightly. This pin is controlled by turning the gauge clockwise until it pierces the can. But you don't want to do this until you're ready, so be sure to back it all the way out before you assemble everything.

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Assembling the Recharge Kit

Attach the hose to the pressure gauge.
Matt Wright

With the piercing pin safely retracted, assemble the pressure gauge and the kit. Screw the rubber hose onto the pressure gauge and tighten it. Now's also a good time to calibrate the gauge. This is a basic procedure. On the face of the gauge, you'll see different temperatures. All you need to do is turn the calibration dial to the outside temperature, which you can check with a weather app on your phone or an old-fashioned weather thermometer. 

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Locating the Low-Pressure Port

Locate the low pressure port, that's where your action will be.
Matt Wright

Your air conditioning system has two ports, low-pressure and high-pressure, depending on where you are in relation to the compressor. You'll be recharging your AC through the low-pressure port. You should consult your owner's manual to be sure, but your vehicle will have a cap over the pressure ports. One cap is labeled "H" (for high pressure) and the other is labeled "L" for low. As a further safety measure, the ports are different sizes so you physically cannot attach the pressure gauge or hose to the wrong port.

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Clean the Low-Pressure Port

Carefully clean the low pressure port.
Matt Wright

If any debris gets into the compressor it can cause it to fail prematurely, and this can be expensive to repair. To be safe, you should clean the outside of the low-pressure port before you remove the cap, and then again after the cap is removed. This may seem like overkill, but one grain of sand can ruin a compressor.

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Testing the Pressure

Pull the sleeve back and slide the fitting onto the low pressure port.
Matt Wright

Before you attach the hose, you'll need to turn the gauge clockwise until it stops tightly. This will seal the gauge off so you can safely attach it to the AC port.

With the port cleaned, you're ready to attach the rubber hose that links the car to the pressure gauge. They use a quick and simple latching mechanism. ​To attach the hose to the low-pressure port, pull the outside of the fitting back, slide it over the port, then release it.

Now, start the engine and turn the air conditioning on high. Take a look at the gauge and you'll see how much pressure your system is building. Give it a few minutes to get the pressure up and equalize, then you can take an accurate reading.

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Preparing the Can

Turn the gauge clockwise to pierce the can.
Matt Wright

Remove the hose from the port. Turn the gauge counterclockwise again to retract the piercing pin. Screw the pressure gauge assembly onto the can of refrigerant tightly. Turn the gauge clockwise all the way, and you will hear the pressurized can pierce.

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Adding the Refrigerant

As you add refrigerant, rotate the can back and forth.
Matt Wright

Reattach the rubber hose to the low-pressure port on the AC line. Start the engine and turn the AC to high. Give the system a minute to pressure up, then turn the gauge counterclockwise to start releasing the R134 into the system.The area of the gauge that corresponds to the outside temperature will tell you when the system is full.  As you add refrigerant, slowly rotate the can back and forth.

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Finishing the Job

This system reads a low 10 pounds, so keep adding.
Matt Wright

Keep an eye on the gauge as you fill and you'll get the right amount of refrigerant in. Don't worry if you are off by a few pounds. When you're finished filling, don't forget to put the cap back on the low-pressure port to keep gunk out. Even if the can is empty, hold on to the pressure gauge. You can use it to check your AC system pressure and next time you add refrigerant you will only have to buy the can.