Rick's Free Auto Repair Advice

Tips to recharge your car AC with R-1234a

Learn some pro tips to recharge your car AC with R-134a

If your car’s AC is low on refrigerant, you can buy a DIY kit and recharge it yourself. DIYers do this every summer, but many of them make mistakes that come back to haunt them later on. Here are some pro tips to recharge car AC with R-134a.

But first a word of warning:

All auto compressors rely on oil to lubricate the piston rings, scroll seals or vane seals. The oil is carried throughout the system with with refrigerant. When your system is low on refrigerant, it’s because you have a leak. And when refrigerant leaks out, so does OIL. If you just recharge your AC without replacing the oil, you will destroy the AC compressor. And once the compressor goes, you have to replace the receiver/dryer, condenser, expansion valve and flush the system. Keep that in mind as you consider doing just a recharge. Because if you just add refrigerant, you’ll be running the compressor when it’s low on oil.

Avoid this common mistake — Overcharging

More refrigerant will not make your car’s AC cool better

The proper way to recharge a car’s AC system is by evacuating the refrigerant and recharging by weight. But I know you won’t do that. So before you slap on a DIY kit, know this: R-134a AC systems have an under/overcharge tolerance of just 2-oz. If you overcharge the system, you’ll LOSE cooling ability.

Worse yet, it’s easy to overcharge your car’s AC with a DIY kit because the kit comes with just a low side gauge. It’s impossible to get the right charge using just the low side pressure reading.

The only way to properly charge a car AC system using pressure is by using a manifold gauge set, with a thermometer in the dash and one in front of the vehicle.

However, if you don’t want to buy a manifold gauge, here’s a way to get close to the right charge with your DIY kit

Buy a dial thermometer and stick it in the center duct on your dash. dial thermometer for auto AC use

Turn the AC to MAX. Set the HVAC to recirculate. Close the windows.

Start the engine and note the reading on the thermometer. Squeeze the trigger for about 20-seconds and then release it. It takes a while to notice the effects of adding refrigerant. So monitor the thermometer to see how much the temperature dropped.

The center dash temperature will never get below 34°F. You’ll be lucky if you can get it down to 40°F. So add more refrigerant; stopping and starting until the thermometer stops moving after a shot.

If the thermometer doesn’t drop after you’ve added refrigerant, your problem isn’t a refrigerant volume issue. it still isn’t cool enough forMany DIYers aren’t that patient and keep injecting more and more refrigerant. They wind up with an overcharged system and no cooling.

If you’ve added a half can or more of R-134a refrigerant, you’ve got a major leak and this recharge isn’t going to last

If you’re adding more than a few ounces of refrigerant, you’ve not only have a sizeable leak, but your AC system also has air in it. An AC system can’t work properly with air inside. Worse yet, running your AC system with air inside can actually damage the system. The moisture in the air reacts with the refrigerant and oil to create acids and sludge, which can clog small passages in the condenser and expansion valve.

If your car’s AC system doesn’t cool better after injecting a few ounces of refrigerant, stop and get the system fixed properly. The leak won’t fix itself and the refrigerant you just added is going to leak out anyway.

Don’t Jump/hot wire the low pressure switch to get the AC compressor running

Remember, the refrigerant carries the oil. If the pressure is so low that the low pressure cut off switch won’t activate the compressor clutch, you’ve got a serious leak.

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.

See the tips below to learn how to add refrigerant when the compressor clutch isn’t engaged.

Don’t add refrigerant by turning the can upside down

All DIY AC recharge kits are designed to inject refrigerant vapor into the low side of the system. If you turn the can upside down you’ll be injecting liquid refrigerant into the low side. If liquid refrigerant gets into the compressor it’ll self destruct.

Don’t use a DIY recharge kit that contains a stop leak product

When AC stop leak was first introduced, the manufacturers claimed it wouldn’t damage the recycling 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 and it ever has to go into the shop for AC repair, you’ll be charged a substantial fee to remove the contaminated refrigerant. In other words, you’re taking a big chance by adding stop leak, because it rarely works and it costs extra to remove.

Mistake #6 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 on the inside surface of the evaporator and condenser acts as insulation actually reduces heat transfer whcih reduces cooling. Don’t go overboard on oil.

Mistake #7 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.

Mistake #8 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.

Car AC recharge tips

Tip #1 Invest in a real manifold gauge set

It’ll allow you to diagnose the system much better than using the cheap gauge that comes with a DIY recharge kit.

Tip #2 Correctly read a DIY kit gauge

The DIY recharge kit gauges have a green, yellow, and red zone to indicate proper pressure levels. The proper way to read the gauge is when the compressor is running, not when you’re injecting refrigerant and not when the compressor shuts off.  

Tip#3 Monitor center duct temperature with a dial thermometer

Low side pressure isn’t a very good indication of system charge level. But cold air coming out of the center duct is a much better indicator. Shove a dial thermometer into the center duct and watch the temperature as you inject refrigerant. If the center duct temperature drops below 40° and you’re getting close to using half the can. Stop. That’s as good as it’s going to get.

Tip #4 How to inject refrigerant if the compressor clutch isn’t engaging

When the compressor is running, it’s sucking refrigerant out of the evaporator. That’s when you should be injecting refrigerant. But if the compressor isn’t running, it’s probably because system pressure is too low to allow the compressor clutch to engage. But you can still inject refrigerant!

Injecting refrigerant when the compressor isn’t running will take MUCH longer because the refrigerant will have to seep through the compressor’s pistons. But it can be done. Here’s how:

With the recharge can in the upright position, squeeze the trigger and watch the pressure gauge. When it stops falling, release the trigger. Let the sit sit untouched for about 5-minutes. Then start the engine and switch on the AC. If the compressor clutch engages, you can continue charging normally.

If the clutch doesn’t engage, repeat the above procedure. At a certain point, the AC can will be cold and frost will develop. Dip the can in a bowl of warm water and try injecting more refrigerant.

If you inject more than half a can and the compressor still doesn’t engage, stop. You’ve got more serious problems going on and this DIY kit won’t fix your AC system.

See this post or this post on what to do if your AC compressor clutch won’t engage.

WARNING: Don’t recharge 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.

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

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Posted on by Rick Muscoplat



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