Why AC Compressor Runs, But Won’t Take Refrigerant?


Usually, recharging your car’s A/C system is a pretty simple procedure. You turn on your car’s A/C system so that the compressor is running, attach a can of refrigerant to the system’s low-pressure service port, and fill the system with refrigerant until it reaches the right pressure.

However, sometimes you may find that even though the compressor is running, the system will refuse to take any of the new refrigerant. When this happens, it’s usually the result of too much air or oil being present within the system.

In this article, we’ll be explaining how exactly this happens and what you can do to solve this issue, and we’ll also share some other things you should know about your car’s A/C system that you may find helpful if you want to work on it yourself.

How Does My A/C System Work?

Before we get more into how air and oil can end up trapped in your A/C, let’s take a quick moment to briefly discuss how your A/C actually works. 

When gaseous refrigerant enters the system, the first thing it does is pass through the compressor. The compressor, as its name suggests, compresses the refrigerant and turns it from a gas into a liquid.

After the refrigerant leaves the compressor, it contains a lot of heat and won’t be good for actually cooling the car. Therefore, the refrigerant then gets sent to the condenser, which maintains the pressure of the refrigerant but lowers its temperature.

After this, the refrigerant passes through the receiver, which contains desiccants and filters that remove water and debris from the refrigerant. If water were to get inside the A/C system and end up freezing, it could potentially cause a lot of damage.

When the refrigerant exits the receiver, it hits the expansion valve which turns the refrigerant back into a gas and cools it off even more. Then it enters the evaporator, where it absorbs all the heat from the surrounding air, leaving only cool air behind. A fan blows over the evaporator and sends this cool air into the passenger compartment.

Finally, the refrigerant re-enters the compressor and the cycle begins all over again.

Read: How to Release the Refrigerant From Your Car’s Air Conditioner?

How Does Excess Air and Oil Get Into My A/C?

As we’ve mentioned, if your A/C compressor runs when you try to charge the system but fails to actually draw in any refrigerant, it often means that excess air or oil has become trapped in your A/C system somehow. But how does this happen?

If there’s too much air in your A/C system, it often means there’s a leak somewhere within the system. Air can also enter your A/C system if you fail to charge or drain the system properly.

On the other hand, too much oil in your A/C system is almost always the result of human error. It could be that you filled the system up with too much oil to begin with, or that you failed to completely drain the system of old oil the last time you added some to the system.

How to Check for Leaks in Your A/C System?

If you suspect that your A/C system has a leak in it somewhere, one of the first things you should do is test it to determine if this is indeed the case and if so, where the leak is. 

There are a couple of different methods you can use to check for leaks; one involves using an electronic leak detector, and the other one involves using a dye kit. Let’s quickly go over how each of these methods works.

Electronic Leak Detector

Electronic leak detectors are better than ever at detecting leaks, and they offer an advantage over using detection dye because they can provide a much quicker answer as to if a leak is present and where. They’re also more convenient to use, since you don’t have to add any extra substances to your A/C system.

Electronic leak detectors tend to work in a few different ways. Some leak detectors contain sensors that can detect leaks based on if certain chemicals are present in the air, while others can detect refrigerant in the air based how how it affects an electrical signal. Other leak detectors use ultrasonic technology to actually listen for leaks.

It’s worth noting that electronic leak detectors only work when you get the sensor right up close to the source of the leak. If the leak happens to be in a place that is not normally visible or accessible, the detector may not be able to find it.

Leak Detection Dye

Leak detection dye, on the other hand, takes a lot longer to work but can potentially be a more reliable way to detect leaks in your A/C system. To use leak detection dye, you need to add it to your A/C then spend some time driving around with it on. This will allow the dye to fully circulate within your system.

The dye in leak detection kits is designed to that it glows under a UV light. After you’ve driven around for long enough, the dye will start to leak out of any holes in your A/C system. This will make it way easier to find any hidden leaks, since dripping dye will leave a trail straight back to the source of the leak.

When using leak detection dye, there are a few things to keep in mind. The first is that you need to use the right kind of dye for the type of refrigerant in your system. You also don’t want to use too much dye, since this can end up overcharging your A/C.

Read: What Happens If The Car Engine Coolant Is Low?

How to Vacuum Your A/C System?

If there’s air or oil trapped in your car’s A/C, you’ll have to make sure all of it is removed before attempting to charge your A/C again. Bear in mind that you’ll need an A/C vacuum pump and a refrigerant gauge manifold set before you can do this, but otherwise this is an easy procedure that you should be able to do on your own.

  1. Make sure your car is totally switched off and that the A/C is also set to off.
  2. Connect the refrigerant gauge manifold set to the low-pressure service port on the A/C system.
  3. Connect the vacuum pump to the refrigerant gauge manifold set, and allow it to run for at least half an hour. Keep an eye on the vacuum level while doing this.
  4. Close the valve on the refrigerant gauge manifold set and switch off the vacuum pump. Leave everything as it is for another half-hour, and continue keeping an eye on the vacuum level. If it changes at any point during this time, it means there’s probably still a leak somewhere in the system that needs your attention. If the pressure remains the same, you’ve successfully vacuumed your A/C!

How to Recharge Your A/C System?

Now that you’ve finished vacuuming your A/C, it’s time to add fresh refrigerant back into it. Make sure when adding new refrigerant to use the right kind for your vehicle.

  1. Disconnect the hose from the vacuum pump, and attach it to your keg or can of replacement refrigerant. If your refrigerant comes in a keg with a valve, open the valve and turn the keg upside down, but if it comes in a can then just turn the can upside down.
  2. Once the two gauges on the refrigerant gauge manifold set display the same pressure reading, that means the refrigerant is ready to be put into the system. Start your car’s engine, and turn the A/C on to its coldest temperature and highest fan speed.
  3. Partially open the valve on the low-pressure line to allow the refrigerant into the system. The compressor will cycle on and off when you do this, since there should be no other refrigerant present.
  4. Continue adding refrigerant until the compressor stops cycling. You should also use the gauges on the manifold set to determine what the internal pressure is, making sure not to overcharge the system.
  5. To correctly remove the refrigerant gauge manifold set after you finish charging the A/C, turn the engine completely off and then turn off the valves connecting the manifold set to the various service ports on the A/C.
  6. Once the valves are shut off, simply pull on the connectors to release them from the service ports. Replace the caps on the service ports, and you’re all done!

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