Is your car’s air conditioner turning on and off constantly? This frustrating issue can make your car’s interior hot and uncomfortable. In this guide, we’ll discuss the common causes of AC compressor short cycling and how to diagnose and fix this problem yourself.
If you have a preliminary knowledge of AC compressor and clutch components, you can jump straight to the potential causes section.
- Insufficient refrigerant pressure is the most common reason for AC compressor cycling every 5 seconds. Use a pressure gauge to confirm.
- An overpressurized AC system can also cause short cycling. Check for clogged components or overcharged refrigerant.
- Faulty AC pressure switches give false readings, turning compressor on/off. Test with multimeter.
- Engine overheating indirectly causes cycling by heating cooled air. Check cooling system.
- Compressor clutch slipping from high pressure, lack of lubrication, oil on plate, loose belt, or increased air gap causes cycling.
- Bad electrical connection to compressor clutch coil can cause intermittent cycling. Check wiring and coil resistance.
What You Will Learn:
My Personal Experience With Car AC Compressor Cycling On and Off Issue
Last summer, my uncle’s Honda Civic’s AC started blowing hot air. The compressor was cycling on/off repeatedly. Using gauges, I found the refrigerant pressure was too low. Tracing the system with a UV light revealed a small leak in an AC hose.
I replaced the worn hose, recharged the refrigerant to the proper level and the AC worked great again all season
How Does Car AC Compressor Work?
The car AC compressor works by compressing the refrigerant gas in your car’s AC system.
The refrigerant, in this case, is usually a combination of Freon and oil. Basically, the oil is mixed with the freon by the manufacturer so that it also lubricates the compressor when it flows through it.
The AC compressor pulley is connected to the serpentine belt and is used to turn the piston of the compressor when the pulley is engaged by the compressor clutch. The piston is used to compress the refrigerant gas, which increases the pressure and temperature of the gas.
The serpentine belt is connected to the engine to supply power to the AC system. It is a single belt that runs across all of the pulleys in your engine.
The compressor pulley is mechanically connected with the engine. So, it always rotates when the engine is turned on as the crankshaft is also rotating. The AC compressor will only run when the electromagnetic clutch plate will engage with the compressor pulley. This happens when the current flows through the electromagnetic coil of the compressor clutch.
If you look at AC compressor pulley in the image below, it will have slots. The slots allow the magnetic field from the compressor clutch coil to pass through and pull the compressor clutch plate inward.
The compressor clutch plate (shown in the image below) consists of springs, a hub, and a friction plate. The hub is connected to the AC compressor shaft.
When the friction plate of the compressor clutch engages with the pulley, the rotation of the pulley is transferred to the compressor via that hub. The springs connect the hub to the friction plate and mate directly to the pulley friction surface.
I’m also attaching a short Youtube video in which there is a demonstration of the working of a car AC compressor:
Bonus Read: Car sputtering and shaking when AC is on
Causes Of AC Compressor Cycling On And Off
Here are the causes of AC compressor cycles on and off every few seconds:
1. Low Refrigerant Charge
When the refrigerant charge in a car AC system is low, the low side pressure will drop below the level the compressor can maintain. This causes the compressor to cycle on and off in order to maintain the pressure balance.
Note: Low-side pressure is part of the AC system between the evaporator outlet and compressor inlet. It’s also termed as the suction pressure of the AC compressor.
If the compressor runs on low refrigerant, it can also lead to more wear and tear on the compressor as the refrigerant also plays the role of lubricating the compressor.
With the engine running and air-conditioning on, the low side pressure on a car AC system should typically be between 25-40 psi.
When you increase the engine RPM, the low side pressure decreases and discharge pressure (at the outlet of the compressor) increases.
All air conditioning systems use a closed cycle in which refrigerant is pressurized to flow through the system. If there is a leak in the system, the pressurized refrigerant will be released, causing the refrigerant charge to become low.
How to spot?
To spot low refrigerant charge in the car AC system, you should check low-side pressure using the pressure gauge kit with the engine running.
The leaks in the car AC system can happen due to:
- Faulty seal of condenser, evaporator, and compressor
- Damaged O-rings
- Worn-out hose
You can recharge the A/C system with a refrigerant that has a dye in it so you can trace all the hoses and connections when the system leaks down again using UV light. You can also pressurize car AC system with air and spot refrigerant leaks using soapy water.
Moreover, if evaporator coils are icy, it also indicates low refrigerant levels. This is because when the pressure drops inside evaporator coils due to low refrigerant, the moisture in the air accumulates and freezes on the evaporator coils. This is the basic Physics principle. If the pressure is lower, the freezing point of water increases.
2. Overpressuzied Car AC System
The first thing to check if your car’s AC is cycling on and off every five seconds is the high-side pressure. If the high-side pressure is too high, it can cause short cycling of the compressor.
When the AC compressor is overpressurized, it has to work harder to keep the refrigerant moving, resulting in the compressor cycling on and off every few seconds. This symptom is especially noticed if you have a small engine like 1000 to 1300CC.
Note: High-pressure side is the region between compressor discharge and evaporator inlet.
With the engine running and the AC compressor engaged, the high-side pressure is around 200 to 250 psi at 90 degrees Fahrenheit ambient temperature. When you increase engine RPM, the high-side pressure of AC compressor also increases as the AC compressor rotates at higher speed.
This is because the AC compressor is directly connected to the engine’s crankshaft. Due to this reason, the AC compressor is disengaged when you rev too high to prevent the car AC system from overpressurizing.
How to spot?
When an air conditioning system is overpressurized, it means the high-side pressure is too high. This is usually caused by a blockage in the air conditioning system, such as a clogged condenser or a faulty expansion valve.
Other causes of an overpressurized car AC system include:
- Clogged expansion valve
- Clogged condenser
- Malfunctioning condenser fan
- Overcharging of refrigerant
The purpose of an expansion valve is to cool the refrigerant and reduce its pressure. If the expansion valve is clogged with dirt and other contaminants, the compressor has to work hard to flow refrigerant through it. Due to this reason, high-side pressure increases. The same is the case with the condenser.
The purpose of a condenser fan is to blow air over the condenser to cool down hot refrigerant and convert it into liquid state after it is pressurized by the compressor.
If the condenser fan is clogged or malfunctioning, it will not run properly. As a result, the condenser couldn’t get rid of the heat of the refrigerant, causing an increase in pressure in the AC system.
Similarly, if you’ve overcharged the car AC system with refrigerant, it will cause an increase in pressure.
Usually, the signs of an overcharged AC system are loud squealing noises from the compressor pulley. So, in that case, you should purge the AC system and charge it with the proper amount of refrigerant recommended by the manufacturer.
3. Faulty AC Pressure Switches
An AC pressure switch is a safety device that monitors the pressure in the AC system. It is made up of a diaphragm, a spring, and a switch.
When the pressure switch is off, the current will not flow through AC compressor coil. As a result, the compressor will not engage.
The pressure of the AC is monitored by the diaphragm, and when the pressure reaches a certain level, the switch will be triggered and will turn the compressor off.
Most AC systems have two pressure switches, a low pressure switch and a high pressure switch.
When the pressure in the system is too low, the low-pressure switch will be triggered, and the compressor will be turned off. This is done to prevent the compressor from running dry, which can cause damage to the compressor.
When the pressure in the system is too high, the high pressure switch will be triggered, and the compressor will be turned off. This is done to prevent the compressor from overheating, which can also cause damage to the compressor.
If either the low-pressure switch or the high-pressure switch is faulty, it can cause the short cycling of the AC compressor. This is because the faulty pressure switch will keep sending false readings to the engine’s computer.
How to spot?
To test the AC pressure switch, you can perform these steps:
- Turn the AC on to full-bast mode.
- Connect one end of the multimeter’s test leads to the wire of the AC pressure switch and the other to the ground.
- Turn the multimeter to the Ohm setting.
- Start the car and turn on the AC.
- The multimeter should read zero as the pressure switch is closed when the AC is on and an open circuit when the switch is open. If the multimeter reads differently, the switch may need to be replaced.
4. Engine Is Overheating
Engine overheating does not control engaging and disengaging of AC compressor i.e. AC compressor will remain engaged regardless of the engine temperature.
However, if the engine overheats, it will also increase the temperature of air that was cooled down by the evaporator. As a result, you’ll feel hot air from from the AC vents, and you’ll assume that the AC compressor is disengaging.
There are several potential causes for an engine to become overheated. The most common causes include a damaged radiator, low coolant levels, faulty thermostat, blocked radiator, or a faulty water pump. All of these issues can cause your engine to overheat and lead to serious damage.
5. Slipping Clutch of A/C Compressor
The AC compressor clutch is an electromagnetic device that engages and disengages the air conditioning compressor.
Clutch plate is designed to fit snugly with the compressor pulley. If the clutch of A/C compressor is slipping, it will cause the car AC compressor to cycle on and off every few seconds.
How to spot?
There are following causes of a slipping clutch of AC compressor:0p
- High discharge pressure
- Lack of compressor lubrication
- Oil on compressor clutch plate
- Loose serpentine belt
- Increased gap between clutch plate and compressor pulley
Your car AC compressor relies on a certain amount of pressure to keep things running smoothly.
When that pressure is exceeded, it can cause the compressor clutch to slip. This is because the compressor has to work hard to push the refrigerant and magnetic clutch coil does not have enough magnetic force to keep clutch plate engaged with the compressor pulley.
Similarly, if the compressor does not have proper lubrication, it will overheat and have increased friction between its components. As a result, it will also cause the compressor clutch to slip and disengage the compressor.
Moreover, if there is oil on the compressor clutch plate, magnetic force from clutch coil will not properly exert on the clutch plate.
The clutch plate is made of steel that is attracted to the compressor pulley under the action of magnetic force from the clutch coil. So, you need to make sure that the clutch plate of the compressor is oil and dirt-free.
If the air gap between the friction plate of the clutch and the pulley is increased, the magnetic field will not be able strong enough to pull and tightly hold the plate against the pulley. As a result, the AC clutch will slip and cause short cycling of the compressor.
To check the clearance between the compressor pulley and the friction plate of the clutch, you can use a feeler gauge.
Make sure to check the gap when the engine is not warm. The nominal air gap settings between pulley and friction plate nominal can vary between 0.3 mm to 0.8 mm.
If the air gap is greater than 1.0mm, you need to change the clutch assembly. When you remove a clutch plate, you will see a shim (a small metal disc).
The shim sets the desired gap between the pulley and friction plate. You can adjust the air gap with a shim of different thicknesses.
6. Bad Electrical Connection Of AC Clutch Coil
AC clutch coil uses 12v current from the battery to get magnetized and pull clutch plate towards the magnetic pulley.
In electrical connection, there can by intermittent electrical faults due to damaged insulation, exposure of wire and connector to the moisture, and loose connections due to damaged harness connector. So, due to these intermittent faults, AC compressure starts cycling after 3 to 4 seconds.
How to test?
To test for a short-to-ground compressor coil circuit, set a digital multimeter to the ohms scale and touch one lead to a clutch coil terminal and the other to a ground point on the compressor.
If there is a short circuit, you will not see any conductance. Similarly, perform the test for the other terminal of the coil.
After that, check the resistance across the terminals of the compressor clutch coil. If the resistance is less than 3 ohms or more than 5 ohms, it means the clutch coil is bad.
Does Throttle Body Affect AC?
The question of whether a throttle body affects car AC is one that can be answered with a resounding “No” – but it’s a bit more complicated than that.
The throttle body is an important part of the engine’s air intake system. It controls the amount of air that enters the engine, which is then mixed with fuel and burned in the cylinders to create the power that turns the wheels.
If the throttle body isn’t working properly, it can cause the engine to run rough, which reduces performance and fuel efficiency.
When the engine is running rough, car’s AC system puts strain on the engine due to the increased demand for power. This can reduce the cooling power of the air conditioning system, making it less effective at cooling the cabin.
Types Of A/C Systems in a Car
In a car, there are two types of A/C systems:
- Expansion Valve with Receiver/Drier
- Fixed Orifice Tube with Accumulator
Both A/C systems have a compressor, condenser and evaporator. Both the orifice tube and expansion valve are placed between the condenser and evaporator.
Both orifice and expansion valve cause pressure and a temperature drop of the refrigerant, but the expansion valve also controls the refrigerant flow as it has a spring that controls the opening of the valve.
On the other hand, the orifice tube has a fixed opening. It does not vary the amount of refrigerant flowing into the evaporator the way an expansion valve can. So, in A/C systems with orifice tube, the compressor is on and off (AC clutch engages and disengages) at appropriate times to control the refrigerant flow.
In A/C systems with an expansion valve, a drier is used between the condenser and the expansion valve to capture dirt, rust, or any foreign particles. The drier has also a desiccant to protect the system by removing harmful moisture from the refrigerant.
In the orifice tube system, there is no drier. Instead, the orifice tube is responsible for filtering out the impurities and debris from refrigerant when it comes through its screen. In orifice tube systems, you will find an accumulator on the low-pressure line between the evaporator and compressor.
The function of an A/C accumulator is similar to the receiver/drier. But it is designed a bit differently and is typically much larger. The accumulator separates the liquid refrigerant from its vapors so that it does not harm the compressor. If any liquid enters the compressor, it will damage it.
In summary, AC compressor short cycling is often caused by low refrigerant levels, overpressurization, faulty pressure switches, engine overheating or a slipping clutch.
Proper diagnosis using pressure gauges, voltage tests and visual inspections can identify the root cause.
Refilling refrigerant, replacing faulty parts, adjusting clutch clearances or fixing engine issues resolves the problem. Regular AC system maintenance helps prevent short cycling and maintains cooling performance.
Though unrelated to the car AC system itself, a rough-running engine can indirectly reduce AC cooling capacity.
Some First Hand Experiences Shared By Users In Different Communities
Our team conducted research across various online communities, forums, and subreddits to gather user comments and opinions on “Short cycling of car ac compressor”.
User 1 says:
My Beetle started doing this out of nowhere. I’m not much of a car person, but a mechanic friend suggested checking the AC relay. Replaced it, and voila, the cycling stopped. It was a pretty easy and cheap fix.
User 2 says:
Noticed this weird cycling in my new Palisade. Took it to the dealership since it was under warranty. They found a defective pressure switch and replaced it. Haven’t had an issue since.
User 3 says:
I dealt with this in my Silverado. The issue was a combination of low refrigerant and a leaking hose. Recharged the system and replaced the hose. Problem solved!
User 4 says:
Had this exact issue last summer. My Outback’s AC compressor was cycling every 5 seconds. Turned out to be low refrigerant. A buddy helped me check the pressure, and it was way below normal. Refilled it and the problem was solved!
User 5 says:
I had this on my old Corolla. It was the AC clutch that was wearing out. Replacing the clutch was a bit of a hassle, but it did the trick. The AC has been working smoothly since.