Rick's Free Auto Repair Advice

Car air conditioning recharge

How to recharge car air conditioning

It’s summertime and everybody is asking how to recharge car air conditioning systems. The answers are always the same—recharge it with a do it yourself (DIY) kit from the auto parts store, or (from professional shop owners) DON’T touch it because it’s not a DIY job. The real answer is this; if you want to properly diagnose and fix car air conditioning yourself you either need to invest in some equipment or take a chance with an AC recharge kit. If you try the kit, you may find that all the new refrigerant leaks out and then you’ll be out the $40 and still have to pay a shop to fix it.

A car air conditioning recharge kit works great if you have a small refrigerant leak

A/C expansion valve, A/C condenser, A/C compressor

A/C expansion valve

Not all leaks are created equal. For example, if you live in the cold North Country, it’s really common for seals and connectors to leak a small amount of refrigerant in the winter, The components get really cold and contract and poof, there’s goes some of your refrigerant. Next cooling season your car air conditioning system either blows warm air or barely chilled air because it’s low on refrigerant.

However, if you take it to a shop in the summer when the connectors have expanded and resealed, it’s almost impossible to find the leak.

In this kind of case you may be better off recharging it in the spring rather than spend a small fortune paying a shop to find the mysterious leak. That’s where these do it yourself recharging kits come in real handy–for small leaks that are hard to trace. But be warned, they don’t work if you’ve got a large leak that isn’t caused by cold weather expansion.

A/C evaporator coil, A/C condenser coil, A/C compressor

Evaporator coil (inside your dash)

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.

Let’s not kid each other, there’s no guarantee a DIY kit will work. First off, unless you have a professional gauge set, you really don’t know how much refrigerant leaked out. The system could be completely empty, in which case the leak MUST be repaired and the system evacuated by a vacuum pump before you refill it. If you refill it while air is inside the system, it’ll never cool properly. Worse yet, the moisture in the air will form acids that destroy your compressor, evaporator, and condenser. So you end up with a system that’s totally destroyed.

The part most DIYers miss is that you should set the system to MAX AC and turn the blower motor its highest speed first. Then start adding refrigerant. If you read the directions on the DIY recharging

A/C condenser coil, A/C evaporator, A/C recharge, A/C compressor

Condenser coil (mounts in front of your radiator)

kit can, it’ll tell you to charge the system a bit until you see the AC compressor clutch spinning.

car air conditioning compressor

A/C compressor with pulley and clutch

That’s great, but what if you’ve emptied the entire can (about $40) and it still isn’t turning. Yeah, that’s right, you just wasted $40. On the other hand, if the compressor clutch does start spinning, that’s a sign that the system has enough pressure to override the low pressure cut-off switch. That’s good. You can continue to fill the system until the recharge kit gauge reads the recommend pressure. But you MUST avoid this common DIY mistake. More is NOT better. The charging window on R-134a refrigerant is 2-3 OUNCES. Overcharge the system and you actually REDUCE cooling. Get it? Stop when the gauge reads the right pressure.

What to do if the compressor clutch doesn’t engage

A/C clutch, A/C clutch pulley, A/C clutch coil, magnetic clutch coil, A/C bearing, A/C compressor

A/C clutch, pulley, and magnetic clutch coil

That could mean the system is empty or low on charge or it could mean that the magnetic clutch coil has failed. You have to find out which problem you have before you add refrigerant.

The compressor clutch coil creates a magnetic field that pulls the clutch plate into the pulley and that’s what engages the compressor. So if the coil bites the dust the compressor will never engage.

Test the compressor clutch coil for continuity and short

You can test a clutch coil yourself. First, remove the electrical connector going to the coil. Using a digital multi-meter set on ohms, touch the two leads to the electrical contacts on the coil. You should get a continuity reading. If so, keep one lead on the electrical contact and the other on any metal part of the compressor. If you still get continuity, the coil is shorted to ground. Repeat the test using the other electrical contact on the coil.

A/C receiver, receiver dryer, A/C accumulator

Receiver/dryer (contains a desiccant to remove moisture from the refrigerant)

Got continuity but no short? Great, that usually means the coil is good. What we don’t know is if it’s getting power from your vehicle. This is where it gets tricky. In the old days the AC system would automatically power up the clutch coil any time the AC was turned on and the key turned to the RUN position. But in late model cars, the computer wants to see idle RPMs at a certain level before it’ll power on the compressor clutch. So you may have to jury rig longer leads to your meter so you can move it out of the way and start the engine. This can be dangerous, so do it at your own risk.

If the compressor clutch is getting power but not engaging, replace the clutch assembly before trying to refill the system.

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.





A/C accumulator, A/C receiver dryer, A/C compressor

Accumulator (contains a desiccant to remove moisture from the refrigerant)

Now for the warnings:

Never jumper across the low pressure cutoff switch

Some people think they can place a jumper across the low pressure cutoff switch to hotwire the compressor so it spins while charging. This is a really BAD idea. If the system is empty, that hotwire job will start up the compressor DRY. Pretty soon you’ll have a molten mass of what used to be your compressor. You can add refrigerant to the system even if the compressor isn’t running. It’ll take MUCH longer, but it’ll protect the compressor. So forget the hotwire job and fill the system one-half can at a time. Then try starting the engine to see if it kicks in.

Never overcharge car air conditioning

This is a repeat of what I said above. More is NOT better. The charging window on R-134a refrigerant is 2-3 OUNCES. Overcharge the system and you actually REDUCE cooling. Get it? Stop when the gauge reads the right pressure.

Just click on the link below to pull up a charging pressure/temp chart for R-134 refrigerant.

AC pressure temp chart

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?

Use the correct 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.

Use the correct car air conditioning oil

Each car maker recommends a particular oil and certain viscosity for their system. There is no One Size Fits All oil. 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.

© 2012 Rick Muscoplat




Posted on by Rick Muscoplat

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