How to Troubleshoot a Surge Caused by Car Air Conditioning

When you turn on your car’s air conditioning (AC), you just expect the cool air to flow, smoothly and quietly. You certainly don’t expect it to affect the way the car is running. It’s not at all unusual for the engine speed to drop momentarily when the AC is switched on, but if the engine starts to surge up and down, or even acts as though it’s going to shut off, there is something that needs attention.

Air conditioning operates by circulating refrigerant through a series of devices throughout the car. The refrigerant is driven by a compressor and that compressor requires a lot of power. Automobile air conditioning compressors draw that power from the engine via a drive belt. The compressor may require as much as three to five horsepower depending on how large the system is. That may not even be noticeable if your car has a five-liter V8 engine with power to spare, but if you drive a car with a 1600cc four cylinder, you can always tell when the AC is operating.

Modern cars have systems that are supposed to compensate for changes in the engine load imposed by the AC and other accessories. If your car doesn’t seem to know what to do when the AC is on, here are a few steps you can go through that can help you identify some of the more common issues.

Part 1 of 1: Troubleshooting a car that surges when the AC is on

Materials needed

  • AC thermometer
  • Safety glasses
  • Workshop Manual

Step 1: Check the belts. This is a good place to start because you may not have to go any further. The air conditioning compressor is the largest belt-driven device on your engine. It has two substantial hoses connected to it. It may be driven by the same belt that runs everything else, or it may have a belt of its own.

Check the belt tension according to the workshop manual. Check the operation of any automatic tensioner as well. Check the surface of the belt for cracks or glazing. If the belt is more than five years old, you should replace it or have it replaced for you.

A belt that is slipping because it is loose or worn can cause the engine to overcompensate for the air conditioning load.

Step 2: Check the air conditioning performance. Simply put, your automobile’s air conditioner should be able to pull the temperature down by 30 degrees or more: Meaning, if it’s 90 degrees outside, you should be able to get 60 degree or colder air out of the vents.

Set the recirculation switch to off, so that outside air is coming in and drive the car with a temperature gauge in the dashboard vent. If the air conditioning is not performing well, the engine might be surging because the system is undercharged or overcharged.

If it is overcharged, the load imposed by the compressor will be excessive. If it is undercharged, the AC pressure switch may be cutting the compressor on and off in rapid succession.

Listen to the engine while it is idling and the AC is on. You should be able to hear a substantial click each time the compressor engages. If these clicks are coming less than about 30 seconds apart, your system is probably undercharged.

Air conditioning charging equipment is expensive and complicated, and there are a lot of environmental laws regarding handling refrigerants. If you suspect your air conditioner is not performing properly, and that is causing your car to surge, its best to have the air conditioning system checked professionally.

Step 3: Check the vacuum lines. With any automotive performance problem, vacuum lines are a great place to start. Many things are controlled via engine vacuum and if any of these lines are misrouted or leaking it can lead to a wide variety of issues. Check the vacuum lines for good condition and correct routing using an appropriate vacuum diagram.

Step 4: Check the throttle body. The throttle body is fixed to the intake and controls the amount of air allowed to enter the engine. Often, over time, there will be an accumulation of carbon around the edges of the throttle valve itself. If this carbon prevents the valve from reaching a full closed position it just throws everything off on the idle control system. Look at the stop screw on the throttle lever, and be sure the lever is contacting the screw when not pushing the accelerator.

If it is not, there is probably a large accumulation of carbon on the throttle valve itself. Sometimes you can simply remove the large air hose and clean the throttle in place with carb cleaner and a rag, but more often, the throttle body will have to be removed to be thoroughly cleaned.

Step 5: Check the idle control valve. The idle air control valve comes in many shapes and sizes. On some cars it’s integral with the throttle body, other cars don’t have one at all. Check your workshop manual to determine its location.

If your car was made after 1996, a malfunctioning idle control valve will be signaled by a Check Engine Light. Before that, you’ll have to examine it yourself. The idle control valve has a few moving parts inside it that often become dirty and lock up over time. Sometimes you can get away with cleaning them out, but most often a valve that has been on the car long enough to get jammed up needs to be replaced.

If your car was made before 1992, you can check the function by disconnecting the electrical connector while the car is idling. A properly working idle control valve will default to open position when disconnected, so the car’s engine speed should go up sharply, returning to normal when you reconnect it. If you do this to later cars, it will cause a check engine light and a trouble code that will have to be reset with an automotive scanner.

If you have an appropriate scanner, later model cars have functions that will enable you to operate the idle control valve via the scanner to check its operation.

If you’ve been through these steps, and your car still persists in misbehaving, the cause may be more subtle. In that case, there is no substitute for experience. Your Mechanic can send you a technician with the experience you need to evaluate the problem and help you decide what to do.

Next Step

Schedule Car surges when air conditioning is on Inspection

The most popular service booked by readers of this article is Car surges when air conditioning is on Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE


The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Car surges when air conditioning is on Inspection reviews

Excellent Rating


Rating Summary


26 years of experience
326 reviews
26 years of experience
Dodge Dakota - Radiator Hose Repair - Phoenix, Arizona
Mechanic was great my mechanic sucks, they charged me for heater hose Terry knew nothing about it, the price quoted was $133.48, they added charges for heater hose assessment, which was not done as Terry knew nothing about it and charged me $168.00 he gave me a discount but still came to $158.68 when quote was $133.48, not Terry's fault but still my mechanic site is a rip off, Terry was wonderful
Dodge Ram 1500 - Brake Pads Replacement (Front, Rear) - Phoenix, Arizona
Painless, did job professionally and was prompt and polite.


40 years of experience
31 reviews
40 years of experience
Mitsubishi Outlander - Car surges when air conditioning is on Inspection - Troutdale, Oregon
Very good. Went above and beyond.


23 years of experience
483 reviews
23 years of experience
Nissan Xterra - Car surges when air conditioning is on - Jacksonville, Florida
Brian was very helpful and had a very pleasant and professional demeanor. He made me very comfortable asking question and gave very clear ezplanations.


12 years of experience
56 reviews
12 years of experience
Honda Accord - Car surges when air conditioning is on Inspection - Willingboro, New Jersey
Excellent customer service and is very knowledgeable. I recommend his services to everyone.

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Related articles

Why Does My AC Rattle When I Turn It On?
Common reasons why a car AC system makes a rattling noise is due to a failing AC compressor, worn serpentine belt, or worn out AC compressor clutch.
How Long Does an AC Compressor Relay Last?
Your Your car’s air conditioning system needs to be able to pressurize refrigerant in order to operate. The AC compressor relay is an electronic component that turns your AC compressor off and on. Without it, the compressor will not work,...
How to Buy a Good Quality AC Low Pressure Hose
Air Air conditioning is one of the most important creature comforts in a car. When a component of the AC system malfunctions, you will feel the pain almost right away, and no doubt want to correct it ASAP. The AC...

Related questions

Rattling sound from AC compressor.

The noise you hear may be the internal compressor problem with the swash plate and pistons if the noise you are hearing is when the compressor is engaged. If the noise you hear is when the compressor is not engaged,...

AC blowing warm air.

The AC compressor clutch coil assembly may be inoperative causing your problem. The complete system would need checked. I would recommend having a mechanic, like the certified ones at YourMechanic, come and check it out for you to see what...

Why does a crackling , popping sound come from my vents when I turn on the account or heat .

When you command air conditioning or heat there are mode doors that direct the airflow to the requested place. Positions are floor, windshield, vent /floor, and defrost/floor. The doors move in a housing that has a tight fit. These doors...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 ·