You’ve been in your car for a long time. You have all of the windows rolled down, and finally, decide it’s time to turn on the AC. You notice that your car loses power when you switch on the air conditioner when you do so.
Have you considered what may be going wrong? Well, It’s a common problem with many cars, but don’t worry! It’s not that difficult to fix.
Let’s explain what causes your car to lose power when you turn on the AC. The problem lies with the Idle Air Control Valve, which controls how much air is getting to the engine. When you turn on your AC, it changes the temperature of the air coming into the engine, which affects the air-to-fuel mixture.
The IAC valve senses this change and reacts by changing how much air gets to the engine. Since less air is entering the engine, it isn’t getting enough oxygen-rich fuel to run smoothly. This is why your car loses power when you turn on the AC, and it might even stall completely if the problem gets bad enough.
Now that you know the reason, let’s get into further details of this problem and fix it.
Why Does My Car Lose Power When I Turn On The AC?
Several factors are responsible for this error, including leaks, wiring problems, faulty compressors, and the list goes on. For example, if your car’s hoses are cracked or broken, then that could be causing a loss of power. Also, there can be a short in the wiring, which can also cause an AC drain.
It has plenty of different reasons. Let’s go through them one by one.
Clogged Air Filter
When you turn on the AC compressor, the engine has to suck cooler outside air into the ventilation system. Your engine has an air intake with a filter inside for this purpose. This filter clogs over time and restricts airflow so much that even a full engine load cannot compensate for the lack of fresh cool airflow.
It results in power loss because no cool/cold air will flow through the vent’s infotainment system. There will be no cold air, and the compressor will not engage.
Broken AC Compressor
The air compressor is an essential part of the AC system, and it compresses and pressurizes refrigerant into a dense liquid. So it can flow through small tubing and cool the car. When you turn on the AC compressor, it instantly adds additional load to the engine, which makes it work harder.
If your engine is not powerful enough to run both AC and the engine at full capacity (especially in old cars) – then turning on AC will instantly drop your power.
Low Coolant Level
The AC unit takes heat from the passenger cabin and puts it outside to get cooler air. If there is no heat to pick up, the compressor will not work.
The simplest way to check if your vehicle has a low coolant level or not is to turn on the AC. Also, check if the air coming out of the vents is cold or just lukewarm. If it’s just lukewarm, then your vehicle definitely needs some attention regarding the cooling system.
Various Issues With AC Itself
There may be other issues in your AC system that can cause power loss when you turn on the AC. It may include faulty vent flaps (in case of dual climate), faulty A/C compressor clutch sensor, or faulty wiring in any place inside the ventilation system.
Increased Power To The AC
There may be an increase in power usage of the AC system. This causes a dip in voltage or a drop in amperage. It makes the car’s computer think less power is going to the engine and thus reduces fuel supply. Over time this can eventually damage a car’s engine either due to lack of fuel or overworking it.
Does AC Affect Car Performance?
Most people would say no, as long as I keep my radiator full of fluid and it doesn’t overheat. They might point out that AC reduces engine power, but a power reduction is worth the cold air.
However, there is more to the story. We will explain in detail why AC affects your car’s performance.
Remember Newton’s Law of Cooling? It has two parts:
- When heat transfers from hot to cold, its entropy increases
- Heat transfer decreases if its rate depends on the speed of heat conduction.
These laws apply whether or not you have AC working in your car. First, let’s consider the cold side of your radiator and how coolant moves through it:
When coolant moves from a cold part of the system to a warm one, some heat transfers to the warm part of the system, but that heat transfer is at the expense of the coolant’s ability to transfer heat.
If you are using AC, it will take more time for the coolant to transfer its heat. It is because it needs to absorb more energy before its entropy increases enough to transfer to someone else.
So, if your engine overheats under high load, try turning on your AC. If your car still overheats, then it means something else is wrong with the engine or cooling system that does not concern the AC.
How Much Horsepower Do You Need For A Car AC?
There are two types of air conditioning available on the market – gas-driven and electric-driven systems. Of course, electric-driven systems are more expensive to use, but they are, without a doubt, safer.
Today’s cars need at least 180 horsepower to run the air conditioning unit with 5HP or 10HP. For safety reasons, many car manufacturers recommend much more than that number. For example, to ensure maximum power and reliability, Chevrolet recommends 300 HP for Corvettes.
Most air conditioning units require a working pressure of between 150 and 175 psi for gas-driven air conditioners. For that purpose, the engine has to produce at least 180 horsepower.
This is why it’s always a good idea to have more power than you’ll actually need. Even if your car’s AC works just fine in the hot weather, you never know when it might break down.
Does Turning AC Off Make Car Faster?
Turning AC off while driving a car is not a suitable option as it leads to overheating the engine. As a result, it affects its lifespan. However, from a speed point of view, this may turn out to be a good idea.
Turning off AC has two beneficial effects. Firstly, it causes the cabin to heat up, which results in the expansion of air inside the tires. Due to this, the size of the contact patch with the road surface increases by 33%. This directly increases the vehicle’s grip on the road and its speed.
Secondly, it reduces the wind resistance your vehicle experiences due to the air conditioner compressor. This, when combined with a larger tire contact patch, results in a speed increase of about 1-2 kph.
Viewing the two effects together gives a net speed gain of somewhere between 0.5 to 1.0 mph! Although it’s not a large difference in terms of distance covered over time. Still, every bit counts in the race to beat others.
Downsides?
Turning off the air conditioning can increase speed by allowing more engine power for propulsion. But it also has several negative consequences.
- Your car will stop receiving air conditioning; when you want it back on, you’ll have to turn the AC back on manually.
- The compressor takes power away from the engine when the compressor is running, making your car less powerful. This may not be a big deal if you’re just tooling around town, but during the race, it will cost you valuable time.
- Air conditioning helps cool the engine itself. If you turn off the AC and ignore warning lights that indicate overheating, you risk damaging the engine. It not only shortens its lifespan but also makes it less powerful.
Why Does My RPM Go Up and Down While AC Is On?
RPM (Revolutions per Minute) is a measurement of rotational velocity. It’s used in many contexts – such as car speeds, engine rotation speeds, and fan speeds.
If your RPM goes up and down while A/C is on, it may be due to the load on the engine affecting the cooling fan speed. This is due to the way cooling fans are wired.
Car manufacturers try to be very clever with the wiring of their fan systems. But often, it’s down to cost savings, and sometimes even reliability can suffer as a result. Many modern cars have two or three fan speeds at which they operate. The most obvious one is when you’re just idling, and the fan speed is at its quickest.
When you step on the accelerator, either with or without A/C, it drops down to a slightly slower speed. If you turn off the AC, it drops right back again to another slowest speed, even lower than before. This means in reality, at least three fan speeds are in use.
In our opinion, they do this because it’s a straightforward and cheap solution to what can be a complex problem. It saves having a variable speed control on the fan itself. But, running fans at one speed at idle and another when you’re accelerating is simply not adequate for many cars.
The biggest problem occurs when you’re stationary and the engine runs at 2000 RPM or more. For instance, when you’re waiting to turn right at a busy junction but can’t due to a traffic jam. You’ll find your cooling fan going at its highest speed, and all this does is make the engine hotter and doesn’t cool anything.
Then, as you move away and the RPM goes down to around 2000 or less, your cooling fan speed drops right down too. They don’t wire up the cooling fan system to operate at a fixed rate.
Check Out Idle RPM Fluctuation with A/C ON:
How To Fix A Car That Turns Off When AC Is On?
When the air conditioner is on, it can turn off when you slow down or change gears in your car. This is a common problem, and several possible things can cause this to happen. Here’s how you can fix a car that turns off when AC is on.
Tools Needed
- Multi-meter
- Ratchet set
- Socket wrench (various sizes)
- Carjack
- Screwdrivers (flathead/Phillips)
Procedure
- Find out why coolant is disappearing from your car’s air conditioning system. You’ll need to check for leaks to fix the problem.
- Find out why your car’s blower isn’t working. It may be due to faulty connections, fuses, or switches that need replacing.
- If you find a fuse that is blown, replace it with one of the same amperages. If this doesn’t solve the problem, it could be either a faulty switch or a connection issue.
- Check all electrical links and wiring for wear and tear before making any repairs.
- If you notice that your electrical system is overloaded, you should call roadside assistance to remove any excess load from your car’s battery before attempting to repair the problem yourself.
- If all of your car’s lights are on even though the key isn’t in the ignition, it could be due to a faulty switch that needs replacing. You can find this at an auto parts store or borrow one from a neighbor until you get there.
- Check if AC turns off when driving when the engine is off. Even if it doesn’t, be sure to disconnect cables when working on engine inspection cover bolts. This will prevent sparks and ensure safety while fixing AC problems in cars.
- Once you have finished the necessary repairs, test drive your car to ensure that everything is working properly.
Now, you can fix any problem with your AC turning off when the car is on and put it into gear. However, if the AC still malfunctions, you’ll need to take it to a mechanic or an auto repair shop.
Should I Turn Off My AC Before Turning Off The Engine?
It is not necessary to turn off the air conditioning in a car when it is not in use. In fact, there are several reasons why you should never shut off your car’s engine before turning off the AC. Here are two of them.
To Save Gas
You will save gas by not shutting down the engine first. When you turn on the air conditioner of a running vehicle, it does not produce cold air right away. It is because using some power to run the fan and create cool air.
If you turn off an AC running engine, it will take even longer to produce cool air in warm weather. Thus, you should not turn off the AC before shutting down the car’s engine because it will waste gas in both cases. Plus, it takes time for cooling to start when you restart your vehicle again.
To Prevent Battery Damage
Turning off the AC draws power from the battery and causes damage to the battery when it is not correctly recharged. When you turn off the AC after driving, even though you are not planning on staying for a long time, your car’s computer cannot accurately judge whether you will continue to rerun the AC shortly.
Therefore, if you decide to get out of your vehicle moments later, the computer draws power from your car’s battery to keep running the AC. Without enough recharging, the battery becomes weaker, and it may damage the battery over time due to overuse.
Check Out How an Air Conditioner Can Stop an Engine:
Should I Turn Off My AC Before Turning On The Car?
It is an excellent idea to let the car idle for a bit before turning on your AC. There are two reasons you should do this:
- Letting your engine idle for a few minutes allows it to warm up. When the engine starts, oil sits on top of the cylinders. This oil must be warm and thin enough for the pistons to travel smoothly throughout the cylinders. This is a safety precaution for your engine because it reduces friction on the cylinder walls.
- Turning on your AC lets cold air rush into the cabin of the car. Without the engine running, you’ll be sitting in a cabin full of hot air, and your AC won’t be very efficient. We recommend turning on your ignition and letting it idle for about 3 minutes before turning on the AC.
If you are wondering if will it be bad for your car because of letting unburnt fuel into the catalytic converter? Well, no. Suppose your vehicle is in proper working condition and the catalytic converter is in good condition (i.e., no carbon deposit clogging). In that case, turning on your AC will not damage the engine or release any harmful gases into the environment.
Now, if you’re driving a car that’s malfunctioning, you should avoid turning on the AC to prevent any inconvenience.
Key Takeaway: Now, if you’re driving a car that’s malfunctioning, you should avoid turning on the AC to prevent any inconvenience.
Why Does My Car Idle Rough with AC On?
Theoretically, if your car is idling rough with the AC on then, it means that there is a problem with either one of those two systems. In most scenarios, it turns out to be an issue with the idle control system, which uses various sensors to maintain idle RPM.
Sometimes a faulty sensor or a sensor wire can cause problems and take a toll on the engine. If not, then a problem with the AC system will also cause rough idling and car stalling.
Mostly, it is a problem with the idle control system, so we suggest taking your car to a mechanic ASAP. It takes about an hour and a half for the diagnosis. Also, if the problem with the AC is minor, they may not even need to check it.
How To Fix Rough Idle When AC Is On?
You’re driving down the road with your AC on, and suddenly your car starts to sputter and shake. Well, you’ve got some rough idle. It is usually due to a dirty or clogged air filter or idle air bypass valve. This causes extra resistance for air to pass through the system, causing the engine to work harder, and decreasing engine performance.
Before fixing the problem, it is crucial to diagnose its cause. So, let’s start with a fundamental question: if your engine is idling roughly even with the A/C off, you might wonder, “What does it mean?”
Your car will idle roughly for multiple reasons, but there are only three leading causes of rough idle when the AC is on.
- Your RPM is too low because your engine needs (spark plugs are dirty), or your engine is (plugged fuel filter).
- You might have a vacuum leak that’s causing your engine to stall for lack of fuel.
- Your throttle body might be dirty or stuck and not allow the right amount of air into your engine.
Once you have detected the cause behind the rough idle problem, you can quickly fix it with the help of the following steps.
- Turn off your AC. Keep the car running while you do this because it will help in step 2.
- Pull over in a safe place and pop open your hood. Put the car in park or neutral if you can.
- Locate the air intake on top of your engine. It will be on the driver’s side near the windshield). Follow it to where it leads. This tube leads down to the air filter under the engine in most cars.
- Remove the air filter. It should be right in front of you, or near it anyway.
- Look at your old air filter and see how dirty it is! Then cleanly put your new one back on there. If you’re driving with a dirty air filter, the car isn’t running well. Plus, it can cause a decrease in fuel economy and horsepower loss.
- Once you’ve done that, turn your AC back on and restart the car! You should notice an immediate difference in your car’s performance, assuming that this was indeed what was causing those symptoms.
- Make sure to check for any more issues before getting back on the road by checking all of your fluids, tire pressure, and anything else you should do before getting on the road.
If this doesn’t fix your car, it might have a severe problem that concerns a mechanic.
FAQs
Will a low coolant level affect the AC?
No. Your AC works only with the engine coolant, and it circulates through your engine, absorbs, and carries away excess heat. Then it flows into the radiator to cool off.
Nozzle jets spray a fine mist of this fluid onto the inside surface of the radiator to quickly transfer heat from the hot fluid circulating through it. Hence, your AC system will only use the engine coolant with a mix of anti-freeze.
Your AC does not use or rely on engine oil, and coolant/antifreeze will not cause your AC to break down. Therefore, putting additional coolant/antifreeze into the radiator is perfectly safe without draining it first.
What Is The Normal RPM When The AC Is On?
The normal RPM when AC is on varies because it depends on the type of AC. For example, if you have a window unit, it should be about 1100 rpm. While, if you have central air, it should be between 800 and 1200.
This means that the fan speed for cooling ranges from 1100 to 1450 RPM in a window unit. In contrast, the fan speed for cooling central air ranges from 800 to 1200. An average window unit will be running at around 1100 RPM. At the same time, an average central system will run somewhere between 800 and 1400 RPM.
You must check your AC if it is over 1400 rpm, as it may indicate a power issue or something wrong with the system.
Does Turning Off the AC Give You More Power?
Turning off the AC is great for slowing down heat soak and potentially increasing grip, but it’s not good for horsepower. This is because of the “heat transfer.”
- The hotter your engine gets, the less power it makes.
- Heat transfer is the process of transferring heat away from your engine.
- Air conditioning lowers the incoming air temperature, which decreases heat transfer.
For example, let’s say you are cruising down the highway at 70 mph with your AC off (because it’s broken). The outside temperature is 100 degrees Fahrenheit. The intake temperature is now approaching 200 degrees Fahrenheit. So, the engine temperature will also rise dramatically.
Your car’s computer sees that the engine temperature is too hot, so it reduces power to prevent damage. You are now cruising down the highway at 70 mph with your AC broken and without any horsepower!
Why doesn’t my car accelerate when I turn on the air conditioning?
It is because you are trying to “accelerate” with the AC compressor running. Due to this, the engine power turns the AC compressor flywheel. Rather than using this useless energy, try turning off your AC compressor during acceleration attempts. The car will accelerate faster without the AC on.
This phenomenon has to do with the power vital to turn the AC compressor. The compressor has a great deal of rotating mass since it is about 2 feet in diameter. Even though only about 1/10th of horsepower runs an AC compressor, it makes acceleration very sluggish when the AC is on because it uses a lot of engine power to turn the compressor.
This is why your AC needs to be off anytime you try to accelerate quickly. Anytime your AC is on, it will cause engine power to go to waste while turning the AC compressor instead of accelerating the car.
Why does my car lose power as it warms up?
When gasoline engine vehicles are started cold, they run rich, meaning the air/fuel ratio is richer than stoichiometric (chemically ideal). And that’s what’s necessary to start and warm up the engine quickly, reducing wear and avoiding rough/hard starts.
The excess fuel is “burned off” over the first minute or two of operation. By the way, gasoline engines get warm when the coolant temperature reaches about 185 degrees Fahrenheit. So, when the engine is fully warm, its computer switches to its stoichiometric mapping.
It’s all fine unless you have replaced the oxygen sensor with an aftermarket unit. Also, a unit that’s not rich-range compatible or has a poor signal/noise ratio. This results in the ECU pulling back on fuel and creating a lean mixture under part load.
The result: rough/hard starts and poor idle fuel economy. If the problem persists, your engine can run so lean that it goes into protection mode and shuts down or misfires so badly it seizes.
Final Considerations
Summing it up, the cooling system and many other parts of your vehicle are mechanical systems that require an intake source of air to work properly. When this airflow is suddenly hindered due to blockage, undesirable consequences occur.
Driving through a thick blanket of dust or other environmental factors can cause the car to lose power. But, the primary cause is the airflow obstruction you encounter when you turn on your AC. The air filter works hard all day, protecting various parts of your engine from dirt and debris. So, don’t let it work any harder than by neglecting routine service intervals.
