Why My Car Loses Power When The Ac Is On?

When driving on a hot sunny afternoon, what comes to mind is to wind up the glass and turn on the air conditioner. For me, I love listening blues on hot afternoons. Oh! I know most folks don’t like playing tracks on sunny days.

But what happens if your car struggles when AC is on? That would be quite frustrating, and you would have to switch off the AC and wind down the glass. 

Chibuisi Wisdom, one of my fans on my Facebook page, asked why my car loses power when the ac is on. He’s been in this unnerving situation and understands that switching off the ac will not fix the problem. Instead, it’ll hide it until you turn on the air conditioner again.

I’m dedicating this article to Chibuisi, and I’ll outline the possible causes and how to rectify the problem. So, sit and relax while I walk you through all the possible causes.

Why my car Loses Power when the ac is on (8 causes)

If you turn on your car AC and notice that the engine loses power and regains the lost power once you switch off the AC, you should be concerned.

Locked-up ac compressor, faulty ac pressure switch, and clogged condenser are the common reasons your car loses power when the air conditioner is on. However, a dirty throttle body, bad alternator, or slipping drive belts can cause poor engine power, which will only become obvious when you turn on the ac.

Clogged AC condenser

Clogged AC condenser

The car air conditioning condenser is a heat exchanger. It cools down the refrigerant heated by the AC compressor. It is essential for every working ac conditioning system in a car. 

However, if the ac condenser becomes clogged, it’ll cause your car to lose power once you turn it on. But let’s get this clear; the AC condenser has no direct link with your engine performance. Instead, it affects the entire AC unit, which invariably affects the engine performance.

Here’s how a clogged ac condenser indirectly affects engine performance. The AC compressor, the heart of the AC unit, derives its power from the engine through a drive belt. And since the condenser dissipates heat from the air conditioning system, it can affect engine power and acceleration.

When the condenser attracts dirt or becomes clogged, it won’t correctly dissipate heat from the AC condenser. The refrigerant may overheat because the condenser is not doing its job perfectly. This will make the AC compressor work harder and demand more power, leading to a loss of engine power when the AC is on.

Locked up AC compressor

Locked up AC compressor

The compressor is the heart of the AC unit, and its primary function is to pressurize the refrigerant before sending it to the evaporator. As explained earlier, the compressor connects to the engine pulley via a serpentine belt and uses the engine power. If the compressor becomes faulty, the entire AC unit will not work as it should.

If the compressor locks up, the pulley will not rotate along with the engine pulley, putting too much strain on the engine. This will cause the engine to lose power and acceleration whenever you turn on the air conditioning system. But does turning off ac make the car faster? Yes, it’ll make the car faster in this situation.

The compressor could be partially locked up, and the AC unit will cool the cabin. However, the compressor pulley will not rotate smoothly when you turn it by hand. A seized or locked-up compressor could result from a lousy compressor clutch, defective compressor pulley, or the compressor itself.

Lousy AC pressure switch

Lousy AC pressure switch

Your car air conditioning system has two pressure switches – the high and low-pressure switches. Both switches regulate the refrigerant flow in the system and should be working properly for optimal system performance.

Amongst these two, the low AC pressure switch is likely the culprit. The low-pressure switch is located close to the compressor and monitors the pressure on the low side. The switch will shut off the compressor, preventing it from damage whenever it notices low refrigerant in the system due to low freon level.

If this switch becomes faulty and stuck in the ON position, it’ll allow the compressor to run even when there’s low refrigerant. If this is the case, the compressor will run harder to meet the refrigerant demand in the system. Here’s the thing, the extra power used by the compressor to meet the system demand will cause a loss of engine power and acceleration once you turn on the air conditioner.

Similarly, the high-pressure switch monitors the refrigerant level on the high-pressure line. It is close to the condenser. If it also gets stuck in the ON position, it’ll make the AC run harder and use more power from the engine. So, if your car loses power, but the engine is running when you turn on the AC, you likely have a lousy AC pressure switch.

Weak engine compression

Weak engine compression

Engine compression is the pressure created within the engine cylinders during combustion. It provides enough power by ensuring efficient combustion of the air-fuel mixture. If the pressure inside the cylinder walls becomes lower than it should be, you have weak engine compression.

Weak engine compression can cause poor acceleration and loss of engine power when you turn on the air conditioner due to the extra strain the AC places on the engine. When you switch on the AC, the compressor collects power from the engine to function. This extra power collected from an engine with weak compression makes it lose power.

Slipping serpentine belt

Slipping serpentine belt

A serpentine belt is an essential component in every internal combustion engine. The serpentine belt connects the engine pulley to several engine components like the water pump, power steering pump, alternator, and AC compressor.

The serpentine belt is not designed to last the lifespan of the engine. They will wear out over time due to the stress on them. Most time, a slipping serpentine belt is why your car loses power when you turn on the air conditioning system.

A slipping serpentine belt will emit several signs to let you change it before it becomes worse or even cut while cruising on the highway. Here are the signs that show you have a worn-out or slipping drive belt.

Weak alternator

Weak alternator

Alternators are essential components of an electrical system. Their primary function is to help start the car, keep it running, and recharge the battery as you drive. If the alternator becomes weak, it won’t provide the necessary electric flow to keep the engine running smoothly and power all the electric system components in the car.

Weak alternators can cause vehicle issues, including engine power loss and poor acceleration. However, you may only notice poor acceleration or loss of power when you turn on the AC because the air conditioning system puts more strain on the car.

Other signs you have a weak alternator includes

Dirty throttle body

Dirty throttle body

The throttle body is a crucial air intake system component that regulates the amount of air that goes into the engine and helps control the engine’s power and speed. If the throttle accumulates dirt carbon buildup, it’ll cause a loss of engine power and acceleration.

At first, the loss of power may only occur when you turn on the AC, but as the buildup becomes much, the car will start jerking whether the air conditioning system is on or not.

A dirty throttle body causes poor acceleration because it restricts the amount of air entering the car engine. Restricting airflow is not the real deal. The problem is it affects the air-fuel ratio necessary for a proper combustion process, which causes power issues.

So, if you are wondering, why does my car lose power when I accelerate? You likely have a dirty throttle body or a clogged air filter. Speaking of clogged air filters, it could also be why your car ac is pulling too much power.

Blocked air filter

Blocked air filter

Like the throttle body, the air filter is a component of the air intake system. As the name implies, its primary function is to filter the air that goes into the engine. Without it, the engine will suck in dirt and other particles, which could cause catastrophe to internal engine components.

Over time, the air filter will become clogged from the particles it prevents from entering the engine. When this happens, it’ll restrict the amount of air that goes into the engine, causing an improper air-fuel mixture ratio. Of course, this will lead to poor engine power. However, you may not notice a loss of engine power until you turn on the AC.

What to do if Your car loses power when the ac is on

As I have explained, several factors can cause loss of engine power when the ac is on. One or more of these factors could be the root cause of the problem in any given situation. Hence, it is essential to look at these possible causes when running your diagnosis. My rule of thumb is to start with the most common and easiest fix when diagnosing your car.

Clean or replace the clogged filter

Locate the air filter housing and remove the cover. The filter housing is a black rectangular box close to the throttle body. It also has a hose that connects to the throttle body. Take off the filter and see if it is clogged, and clean or replace it as needed.

Clean the throttle body.

The throttle body is attached to the intake manifold and connects to the air intake housing via a big hose. Disconnect the air intake housing hose to access the throttle body. You can clean the throttle body without removing it if the buildup is not much. But if the buildup is much, you have to detach the throttle body from the intake manifold by removing the three or four bolts that hold it in place.

Clean the deposits with carb & choke, WD40, or any reliable throttle body cleaning solvent. After that, reinstall it following the reverse process.

Check the drive belt.

If your car engine uses multiple belts, pay more attention to the ones that connect to the alternator and the compressor. But if it uses one belt, then you have to check it thoroughly. Check for cracks and how tight the belts are. Adjust or replace the belts if necessary. Also, check the rollers and all the pulleys and ensure they are not rusted.

Check the alternator

Test the alternator by disconnecting the battery to see if it outputs the proper voltage. If not, replace the component or contact your technician to fix it. That could be all you need to resolve the underlying problem.

Flush clogged condenser

The air conditioning condenser looks like the car radiator, and it is located close to the radiator. Examine the component and see if it is clogged. If it is blocked with dirt, have it flush. However, do not disconnect the condenser if you haven’t done it before. Instead, contact your technician to make a proper diagnosis.

Contact your mechanic

Trust me; it’s okay if you don’t want to roll your sleeves and get your hands dirty. And if you have tried the said steps and none of it could resolve the problem, you may have misdiagnosed the issue. So, the best solution would be to have your mechanic run the diagnosis and rectify it.

Final Words

This article has answered Chibuisi Wisdom’s question, why my car loses power when the ac is on? Car losing power when ac is on happens due to a clogged condenser, clogged air filter, locked up the compressor, weak alternator, dirty throttle body, lousy serpentine belt, or faulty AC pressure switch.

I have explained how these factors could cause your car to lose power when you turn on the AC and outlined what to do.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

Recent Posts