Have you been wondering what happens when the RPMs in your vehicle fluctuate when your air conditioner is running? If so, you’re not alone.
The cause of this is due to problems such as the Idle Air Control Valve, air intake system fault, air conditioner compressor, AC condenser, faulty alternator, or AC refrigerant levels.
Here we’ll explore these potential causes in more detail and how they can affect your vehicle’s RPMs.
Idle Air Control Valve
A faulty Idle Air Control Valve (IACV) can cause the engine RPM to go up and down when the air conditioner is on. The IACV is responsible for controlling the amount of air that enters the engine’s intake manifold when the engine is idle.
Its main role is to stop the car from stalling, and if it detects this may happen, it’ll make continual adjustments.
If the IACV is not functioning properly, it can cause the engine to idle at an uneven rate, resulting in the RPM going up and down.
The IACV is an electronically controlled valve connected to the engine’s throttle body. When the air conditioner is turned on, the IACV adjusts the air allowed to enter the engine’s intake manifold.
If the IACV is not working properly, it can cause the engine to receive too much or too little air, resulting in an uneven engine idle and the RPM going up and down.
A clogged or dirty valve is the most common cause of a faulty IACV.
Dirt can cause the valve to become clogged, preventing it from opening and closing properly, preventing the IACV from regulating the amount of air correctly, and causing the engine to idle erratically.
Related: What RPM Should My Car Idle At? – And Why It Matters
Air Intake System Fault
The air intake system provides the engine with the right amount of air. It is composed of four components.
The air filter traps dirt and other particles that could damage the engine. If the air filter is clogged, it can restrict the air entering the engine. This, in turn, causes the engine to run at a lower RPM and forces the IAVC to continually adjust the RPM.
The second component of the air intake system is the mass airflow sensor (MAF). This sensor measures the air entering the engine and sends the information to the ECU.
If the MAF is not working properly, it can cause the engine to run at a higher RPM than normal. This can cause the engine RPM to go up and down when under extra load at idle such as when the AC is on.
The third component of the air intake system is the throttle body. It is responsible for controlling the amount of air entering the engine. If the throttle body is not working correctly, it can cause the engine to run at a higher RPM.
A buildup of dirt or debris on the throttle body usually causes this. Often a spray with cleaner releases it without the need for a replacement.
Finally, the fourth component of the air intake system is the air intake hose. This hose connects the air filter and MAF to the throttle body. If the air intake hose is worn or damaged, it can make a hissing noise and cause the engine to run at a higher RPM than normal as air escapes before getting into the throttle body.
Faulty Alternator
When the air conditioning is switched on, the alternator has to work harder to keep up with the additional load. If the alternator is faulty, it may struggle to keep up, meaning the engine RPM will go up and down as a result.
Several things, such as a worn-out bearing, a bad voltage regulator, a worn-out alternator belt, or a bad connection, can cause a faulty alternator.
If the alternator is faulty, it may not be able to generate sufficient power, leading to the engine RPM fluctuating, especially at idle when the alternator isn’t being turned at a decent rate by the serpentine belt.
The above parts were not AC parts but more general ones that can cause RPMs to bounce more generally.
The parts below are more specific to Ac only.
AC Condenser
When the AC condenser is faulty, it cannot efficiently convert the gas to a liquid state, so the air conditioning system will struggle to cool the air.
This will cause the engine to run at higher RPMs to compensate for the lack of cooling efficiency, and added load on the alternator means an erratic RPM.
Air Conditioner Compressor
The AC compressor is responsible for pressurizing the refrigerant within the AC system.
This pressure helps the refrigerant absorb heat inside the car, cooling it down. When the AC compressor isn’t working to its max, it can cause a fluctuation in the engine RPM.
This is because the malfunctioning compressor cannot maintain the correct pressure, causing the engine to speed up and slow down as the pressure increases and decreases.
A few different things can cause an AC compressor to malfunction. The most common is a worn-out compressor bearing, a cracked or broken compressor housing, or a leak in the AC system.
Unfortunately, Air con compressor fixes can be expensive in both parts and labor.
AC Refrigerant Levels
This causes the RPM to fluctuate as the compressor is trying to maintain the correct pressure and temperature but can’t due to the lack of refrigerant.
When the compressor cannot reach the desired pressure, the engine will start to struggle, and the RPM will decrease.
This is because the compressor cannot reach the desired pressure, causing the engine to work harder to maintain the correct temperature and pressure.
This is often accompanied by an air con that isn’t as icy cold as it once was and a warmer cabin than you would want.
This will cause the RPM to go up and down as the compressor tries to regulate the temperature.
Related:
Car AC Is Slow To Cool? Help and Advice
Erratic Idle Causes – How To Fix Them Help & Advice
Diagnosing All 7 Loud Car Aircon Noises (Full Guide)
In Conclusion
There can be several explanations for why the RPM of a vehicle goes up and down when the AC is on.
It could be due to an Idle Air Control Valve, Air Intake System Fault, Air Conditioner Compressor, AC Condenser, or faulty Alternator. It is also possible that the AC Refrigerant Levels are too low.
