Recharging Your Car’s AC Isn’t That Hard

If your air conditioning really does simply need a recharge, rather than a new compressor, the job is usually pretty painless.

Just because I’m not in southern California like the rest of the CB team doesn’t mean I don’t need air conditioning. Au contraire – Ohio’s season seems to jump from winter to summer with both feet. I drive a lot of older cars, and I like my car to be an icebox inside, so I have some experience recharging air conditioning. I’m happy to report, it’s usually not too hard to do.

If you followed the saga of my $600 Tiburon, you’ll know that I did a heck-ton of work to get the thing presentable. While doing an initial test of the Tiburon’s services on its maiden voyage with the new engine, I noticed the AC didn’t work. Eh, no biggie – most air conditioning systems won’t operate if they’re too low on refrigerant. Some services are too much of a hassle for my mechanic to do whilst doing an engine swap, as he did with this car, so I finish the job myself. Engine swaps involve swapping over accessories, and the AC compressor loses most of its refrigerant in the process. 

Car air conditioning basically works the same way as an A/C unit in your window. First, a gas refrigerant is compressed into a liquid. The compressed refrigerant is warm, so the highly pressurized liquid refrigerant is run through a condenser, which is sort of like a radiator. Outside air passes over the liquid refrigerant in the condenser, cooling it down. From there, the refrigerant is passed through an expansion valve, which makes it gas again, lowering the pressure. This now ice-cold gas flows through the evaporator (usually located in the car’s dashboard), which absorbs heat from the air inside the vehicle, creating cold air. The cold air is blown into the cabin, while the refrigerant flows back to the condenser, starting the entire process over again.

This video from parts manufacturer Denso provides a pretty thorough rundown:

When my mechanic is swapping over accessories, the AC compressor has to come off, as do the refrigerant lines. Although you can cap the lines to some extent, refrigerant loss is pretty much inevitable. 

That’s where these tools come in handy.

Recharging Your Car’s AC Isn’t That Hard
As you can see, the high side has some refrigerant, but the low side is a nearly empty. – Image: Kevin Williams

This AC gauge tool, and the subsequent R-134A needed to recharge the AC system, can be found at nearly any automotive parts store. Amazon sells it, too.

This gauge allows me to replenish or  “recharge” refrigerant from the AC system. My roommate has done this for me on quite a few flips, but this is one of the first times where I really sat down to figure out how to do it myself. I suddenly felt a little silly for outsourcing it so many times – the entire process is pretty simple; I realized could have done this years ago.

First, you’ll connect the gauge at both the “High” and “Low” sides of the AC lines. The Hyundai Tiburon’s were pretty accessible, they’re right there under the hood, and pretty unobstructed. There are even caps indicating which part is which, marked with H and L. Remember, the “H” side is for high pressure when the refrigerant is a liquid. The “L” side is for that gaseous refrigerant, returning to the compressor.

Recharging Your Car’s AC Isn’t That Hard
The red is the “High” side, the blue is the “Low” side. – Image: Kevin Williams

My roommate has a vacuum that can be attached to the gauge which sucks out any refrigerant, water, or any other impurities that might be sitting in those lines.

After extracting that junk out, I turned the vacuum off and waited. The gauge on the low side read a negative value, which showed the system was holding a vacuum. I wanted to see if there was any leaking in the system, so I let everything sit for about an hour or so, and made sure the system didn’t lose any vacuum pressure. The vacuum pressure stayed steady and true, so it looks like there weren’t any leaks. 

Next, I disconnected the vacuum and hooked up a can of R-134A to the low-pressure side, and started the car. With the car running and the air conditioning on, the AC system sucked in the contents of the can. As the pressure in the can is released, the liquid refrigerant turns to gas inside the can, icing it over. Putting my hands on the can would warm it up some, converting the refrigerant back to a liquid, so it could flow into the system. I wish it were summer, my hands were already ice cold from the near-freezing weather, and touching an icy metal can actually hurt!

Recharging Your Car’s AC Isn’t That Hard
Image: Kevin Williams

In all, the Tiburon took about a can and a half of R-134A. Most cars have the AC system’s capacity on the hood, firewall, or even a door jamb. If you’re not sure, check online, or call the dealer.

R134A is bad for the atmosphere, so the cans can be kind of tricky to get open. My roommate uses this tool that clamps down and punctures the can. He insists it’s not legal to be sold in California, so some of you out west might be forced to find to more frustrating ways to hook up a can of R-134A. Sorry, y’all.

But my Tiburon now has ice-cold air, and hopefully if you have a car that really does “just need an AC recharge” maybe take care of that first before listing it for sale… otherwise we’ll all know the compressor’s actually busted. AC recharging on many cars isn’t that damn hard—anyone can do it with the right tools!

Kevin Williams

Kevin WilliamsKevin's been into cars his entire life, anything from the tiny kei cars in Japan, to the maybe not-so-good American barges of the 1980s. He's flipped more than 25 cars, only lost money twice, and has known how to make his dollar stretch as far as it can. If he ain't talking about cars, he's probably snacking on something sweet and cakey. Contact the author here.