Car Air Conditioner Turns On And Off: (Causes & Solutions)

Having a car air conditioner that is repeatedly turning on and off can be a sign of some problems within your car ac system. And, ignoring symptoms like this could lead to costly repairs. That is why we have put together possible causes for why your car AC turns on and off and how it can be fixed.

The most common reasons for your car air conditioner turning on and off repeatedly include low refrigerant level, a defective compressor, bad compressor relay and an overcharged ac. The problem could also be caused by a dying battery, a defective temperature sensor and clogged lines.

Luckily, it’s not hard to diagnose the above causes and while some of these will require technical knowledge to be fixed, you can easily fix many of them.

8 Possible Causes for A Car Air Conditioner Turning On And Off

1)     Out of range ‘freon’ level

Low or low leaking refrigerant accounts for more than 60% of all car ac problems. This means this is a common cause of any ac problem and in particular the short cycling of your ac.

How much freon to put in your car air conditioner depends on the size of your air conditioner. But there is usually a sticker in the car engine’s compartment to tell you how much refrigerant should go into your car air conditioner. Too much refrigerant can damage your compressor.

On the other hand, an overcharged system with the refrigerant can cause a buildup of pressure that can result in turning on and off your ac.

How to diagnose and fill your ac with the correct amount of refrigerant

If you are a DIY person and want to charge your car’s AC with the refrigerant, you can use the DIY refrigerant quick charge kit such as the AC Pro Recharge (which you can buy from most auto stores or online stores).  But there is a more thorough method of doing it that involves emptying the refrigerant from your system before adding new refrigerant.

I wouldn’t recommend going straight to the Quick charge kit method because you risk overcharging your system. It is best to get a gauge and get the readings first. If freon is low, you may want to get a UV dye kit to check for leaks before adding more refrigerant to avoid the refrigerant from leaking out of the system again.

You may also need special light/goggles to see it. In order to locate leaks, look out for oily residue at fittings. In addition to that, an electronic sniffer can also help identify leaks.

The downside of the using the quick charge kit method is that:

1.       Quick charge kits won’t tell you much about how the high side is doing and they can be inaccurate.

2.       That, coupled with the fact that you don’t know how much refrigerant is in the system, increases the likelihood that you’ll overcharge your system. Unlike the old r12 refrigerant that could tolerate an overcharge or undercharge, overcharging or undercharging the R134a system by a couple of ounces can quickly burn up the compressor or pop a hose

3.       There is a high risk of introducing the air into the system. Be sure to keep the engine and the AC running when you are refilling.

2)     Defective compressor relay

A relay is a small device that controls the circuitry of your ac compressor. In short, a relay supplies power to the compressor and the clutch. If the relay is defective, that could cause it to supply intermittent power to the ac compressor and could be the main reason for your ac turning on and off.

How to diagnose a bad compressor relay

In many cars, the ac relay model is the same as one for your fuel pump. If that is the case, The easiest way to find out whether the compressor relay is working or not is by switching it with the fuel relay.

This is a much easier way of testing whether the relay is defective or not. This method is better than using a meter especially if you don’t really understand electricity or don’t have schematic diagrams for voltage reference.

The fix

If indeed the compressor relay is defective, you’ll need to replace it to fix this problem.

3)     Defective Low/High-pressure switch

The low-pressure switch opens when the pressure in the compressor system is too low. That can be due to low freon in the system. However, if you have verified that the freon level is normal and the switch is open, that can be an indication that the low-pressure switch is defective.

On the other hand, the high-pressure switch will normally turn off the compressor if too much pressure is built in the system. Malfunctioning pressure switches can send intermittent signals to the system and that could be causing your car ac to short cycle

Diagnosing the Low/high-pressure switch 

Pressure switches are designed to close or open contacts depending on the pressure. To test whether the pressure switch is defective or not, disconnect it from the connector and measure the voltage output on its two wires. If the voltage is out of range of or is 0 then chances are, you have a defective pressure switch.

The Fix

The solution to a defective pressure sensor is to replace it with a functional one.

4)     Non-Functioning condenser fan

A condenser fan that won’t start can be the reason for the short cycling of your car’s ac compressor. Usually, when you have a fan that won’t start, your car could be running normally when your car is moving (that’s because cool air will blow through to the condenser). But problems will come when your car is at a stop.

There are a few things that could prevent your fan from starting. These include

a)      Blown fuse

 A fuse works by protecting an electrical component from damage by cutting voltage when there is a surge. The radiator fan typically has two fuses, a bigger one that is a 50A and a second smaller one that controls voltage to the fan control module.

 Remember to check both of them and if there is anything blown out, that could mean there are problems with wiring or the fan itself. When you have a blown-out fuse, you can fix this problem by replacing it with a new fuse.

b)      Defective Condenser fan relay

The radiator fan often has a relay connected to it because it uses a lot of power. When this relay becomes damaged, it will not supply power to the fan and that could be the reason the condenser fan is not working. Usually, the fan’s replay is located in the engine’s fuse box, but you can always refer to the manual to find its actual location.

A relay can also be replaced if it’s defective.

5)     Bad temperature switch

Now, a dying thermistor (usually located in the evaporator housing) could actually be sending false signals to the control board. A thermistor senses the temperature and sends signals to the control board when the set temperature point is reached.

A malfunctioning temperature switch could be the culprit for the problem and when it completely dies out, the ac will shut down completely.

The Fix

To rule out bad thermistors, put a jumper between the ends of the switch and see if the ac compressor clutch will engage.

If nothing happens then the problem is probably not with the temperature switch, and you should proceed to the next step.

6)     Clogged lines leading to high pressure

When lines between the high-pressure and the low-pressure sides get clogged, this can cause too much pressure on one side but low pressure on one side. This also causes short cycling of the ac system.

The Fix

Usually, when there is such a problem, you’ll need a professional with special tools and gauges to measure the pressure across your system.

Repairing typically includes cleaning up the lines and replacing the refrigerant.

7)     Bad battery

 If the problem occurs mostly when the engine is not running. When your engine is idling, the compressor could not be getting enough power from the battery and so be shutting off as a safety measure (that’s for a battery that is aged or one that’s dying.)

You may notice that when you are driving, the ac runs normally because the compressor is getting a sufficient supply of power from the running alternator, but the problem only comes in when it is idling.

The Fix

If your problem is similar to this, consider replacing your car battery

8)     Defective compressor.

A compressor could have just had its time and may need a replacement. A lot of times, it’s the smaller issues that can affect how your car air conditioner works such as a worn-out or loose belt. So be sure you have a check on them, if possible, and ensure that the belt is not loose or worn out and must be tight enough.

Otherwise, if nothing helps at all, it’s a sign that your compressor needs a replacement. You can always get a second opinion from a local professional before getting a new compressor.

Final Thought

In summary, we have seen that there could be any number of reasons for your car air conditioner turning on and off repeatedly.  We hope you have figured out the cause for this problem and ultimately fixed it.

Otherwise, we recommend that you engage a local professional to give you some help. Most importantly keep your car serviced on time and don’t ignore any small, unusual car behaviors. The small symptoms if left unchecked can be costly in the long run.

All in all, thanks for reading this guide.

Tim David

HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.