Rick's Free Auto Repair Advice

AC recharge on your car or truck

How to perform an AC recharge on your car or truck

If your car’s AC is blowing cool air, chances are it’s low on refrigerant. In many cases you can fix the problem by adding more refrigerant from a DIY AC recharge kit. Performing an AC recharge on your car or truck isn’t hard, but there are some do’s and don’ts to follow. For example, you can easily overcharge your car’s AC system and that can cause the AC compressor to stall or even self destruct. But more on that later in the tips and warnings section. First, let’s figure out whether your car or truck is a candidate for a DIY AC recharge.

This is one post in a series. If recharging your car’s AC system doesn’t work, check out this post on how to diagnose an AC problem

Can you fix your car’s AC with a recharge kit?

The real answer is no. Your car’s AC system is a sealed system. It doesn’t use up refrigerant (that’s right, it’s called refrigerant, not FREON). If your car’s AC system is low on refrigerant, it’s because YOU HAVE A LEAK. You can perform a recharge, but you haven’t fixed the root problem. Because when you have a leak in an AC system, refrigerant not only leaks out, but the leak allows AIR and moisture in. Air in an AC system ALWAYS reduces its cooling performance and shortens the life of major AC components.   Air compresses differently than refrigerant and doesn’t absorb heat like refrigerant. In other words, air screws up the operation of your car’s AC. Moisture is even worse. 

Every car AC system has a drier or accumulator that accumulator, receiver dryerabsorbs moisture. But there’s a limit to how much it can absorb. Once it reaches that limit, the moisture in the system combines with the refrigerant and oil to form sludge and acid which eventually destroys expensive components. So performing a quick recharge may solve your problem temporarily, but it’s not a fix. Finding and fixing the leak is the real answer to an AC warm air condition.

Some leaks are caused by old hardened O-rings while others are caused by leaks in the condenser or evaporator. If you perform a recharge and the system blows cold for a while and then the AC blows warm, don’t think you can fix the problem with another recharge or an AC stop leak product. At that point, you’ve got a serious air intrusion problem and you need to get it fixed properly.

Candidates for a DIY AC recharge

Not all cars and trucks are candidates for an AC recharge kit. Here’s a list to help you determine whether your car or truck’s AC can be recharged with a kit.


• You live in an area with frigid winter temps and your AC worked last year but doesn’t work in the Spring, you can probably get it working again by adding refrigerant, and

• Your AC compressor kicks in when you turn on the AC, and

• Your AC cools the air slightly, but it’s not as cold as it used to be.

THEN, you should try a DIY AC recharge kit

However, if your car:

• Has been recharged several times already, or

• The AC compressor doesn’t turn on when you activate the AC, or

• The AC compressor turns on but doesn’t cool the air at all,

Then you’ve got a serious problem that must be addressed by a professional.

Avoid these common DIY AC recharge mistakes

All kits have an instruction sheet. Follow it to the letter. If you skip the instructions you can damage expensive components. Here are things to avoid:

Jumping the low pressure switch to get the AC compressor running

The kit instructions tell you to add refrigerant when the compressor is running. If yours isn’t running, it’s because there’s a problem; either the system is way too low on charge, already overcharged or you’ve got other serious problems. See this post or this post on what to do if your AC compressor clutch won’t engage.

WARNING: All mechanical parts in an AC system are lubricated by oil. The refrigerant is what carries oil throughout the system. If you jumper across the low pressure cut off switch, the compressor will RUN WITHOUT OIL! That can cause serious AC compressor wear that dramatically shortens the compressor’s life or it can cause it to self destruct. Don’t do it.

Instead, try adding refrigerant to the system with the engine off. Connect the recharge hose to the low pressure port and squeeze the trigger for a few minutes with the engine off. Then start the engine and turn on the AC. If the compressor starts, then the system was just a tad too low and the small amount of refrigerant you added was enough to overcome the low pressure switch. BUT, if that doesn’t do the trick, throw in the towel—an AC recharge isn’t going to fix your problem. Period.

Overcharging the AC system is a common DIY mistake

This is a big one and most DIYers make it. More is NOT better. AC systems that use R-134a are incredibly sensitive to over-and-under charging. Adding as little as 2-oz too much R-134a from a recharge kit will actually DECREASE cooling!

When adding refrigerant from a recharge kit, take it slowly. It takes a few minutes for the added refrigerant to work through the system. Watch the gauge on the can and don’t go above the recommended pressure.

Liquid charging is another common DIY AC recharge mistake

DIY recharge kits attach to the low pressure port and MUST be charged with gas. Turning the can upside down will cause liquid refrigerant to enter the compressor. Liquid refrigerant doesn’t compress. If you add liquid to the low pressure line, you risk destroying the compressor.

Adding an AC stop leak product is another big mistake

When AC stop leak was first introduced, the manufacturers claimed it wouldn’t damage the reclaiming units used by shops. They were wrong. It does. So most shops now test customer’s cars before they start working on their AC systems. If you’re system is contaminated with AC stop leak, the shop will add a substantial fee just to remove the contaminated refrigerant. In other words, you’re taking a big chance by adding stop leak, because if it doesn’t work, it’ll cost extra to remove it.

Adding too much oil

Since the oil is carried by the refrigerant, when refrigerant leaks out, so does some oil. DIYers often add more oil when they recharge. But too much oil insulates the condenser and evaporator fins and actually decreases cooling. Don’t go overboard on oil.

Using a “substitute” refrigerant

If you want to kill your A/C system, go ahead and refill it with another type of refrigerant. I guarantee you it’ll be dead within a year. Different refrigerants do NOT mix.

Using the wrong AC oil

There is no universal AC oil. Each car maker recommends a particular type of oil and oil viscosity for their system. Add the wrong one, and, you guessed, it—compressor failure.

Don’t mess with car air conditioning in a Hybrid vehicle

The compressors in many hybrid vehicles are driven by electric motors. The coil windings of the motors are cooled by the flow of refrigerant and a non-conductive oil. If you add a DIY can of refrigerant that contains oil (and most of these kits do), you could wind up dead, as in, no longer breathing. I’m not kidding here. This is a job for a pro. Period. End of story.

A/C Pro DIY recharging kit

This one is my favorite recharging kit. Better gauge. Connector just snaps onto the charging port. Reusable gauge (just screw it onto another can). Refrigerant contains a seal conditioner (not a stop leak) to reduce leaks.

Car air conditioning repair tips:

 Tip #1 You can replace all the parts in your A/C system yourself for about $800

That’s right. That $2,500 quote you got from the shop—well if you just invest in some tools, you can redo the whole system AND own the tools for under $1,000. And you’ll be set for repairs on your friend’s cars too.

 Tip #2 Get a vacuum pump

Everyone is afraid of using a vacuum pump.

vacuum pump

Replace the parts, then pull a vacuum with an inexpensive vacuum pump

There’re not that expensive. You can one new or used for around $100. If you have to replace parts in your A/C system, you MUST pull a vacuum for at least one hour after you’ve put it back together. You can OWN a pump for less that you’ll pay a shop.

Tip #3 Get a manifold gauge set

No pro ever refills the system through the low pressure port. They use a manifold gauge and connector the red hose connector to the high pressure port. They connect the yellow supply hose

car air conditioning manifold gauge set

Manifold gauge set

to a side can tap (see tools below). Then they charge the system with the liquid in the can. It goes much faster than using vapor charging.





If a single car air conditioning recharge doesn’t last, fix the leak

Every time the system loses refrigerant, it also loses oil. Lose enough oil and you’ll find up with Black Death. That’s what happens when a compressor starts to self destruct. The metal starts wearing away, mixes with the refrigerant to form a black muck and gets deposited throughout the system. If your system dies from black death and you just replace the compressor, you’ll be replacing the compressor again in a year. You must flush the entire system with a professional flushing kit, and even then you probably won’t get all the black muck out. The only safe way to come back from black death is to replace the entire system. See how much trouble you can get into with those DIY recharging kits?

© 2012 Rick Muscoplat




Posted on by Rick Muscoplat

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