Car AC Fan Speeds Up And Slows Down – Top 5 Fixes In 2024

I recently faced an issue where the AC fan in my car would unpredictably speed up and slow down, causing discomfort during hot weather drives. It was a bit stressful, but I resolved it by checking for common culprits.

Why car ac fan speed fluctuates? (Short Answer)

It could a voltage issue. Voltage or hertz fluctuation, or a grounding problem. Another issue could be a problem with the fan motor or control.

In this post, we’ll delve into the causes behind your car’s AC fan speeding up and down, a situation I personally encountered and addressed

How Car AC Fan Speeds Works?

The blower engine in the air conditioner controls the different fan rotational speeds. The fan motor pulls air from outside the car and pushes it through the AC evaporator to cool it down. The air that has been cooled is then blown into the car through the vents.

How Car AC Fan Speeds Works?

Car blower motor speeds up and slows down? The Rotational speeds of a car’s fans can be changed either by hand or automatically. The driver can use the AC settings to choose the fan’s speed in manual mode. On the other hand, in automated mode, the fan speed adjusts according to the ambient temperature inside the vehicle and the driver’s chosen temperature.

Also Read: Car AC Takes A While To Turn On

Reasons Why Car AC Fan Speeds Up and Slows Down?

When your car’s AC fan speeds up and slows down, it can be a perplexing issue. I personally faced this challenge and researched from different forums like Quroa, Reddit etc, to understand the various reasons behind it.

1. Clogged Air Filters:

Why car ac fan slows down? According to Reddit and Quora users, a common cause of fluctuating car AC fan speed is a clogged cabin air filter. Dirt and debris hinder airflow, compelling the fan to vary its speed to compensate for the restricted air intake. This can impact the car’s ability to maintain the desired temperature.

Clogged Air Filters
source:Atlanta Car Care

2. Malfunctioning Blower Motor:

Car Blower Motor Speeds Up And Slows Down? The first one is after many years of use, the blower fan wears off. The fan motor moves air through the air conditioner and into the car’s cabin. If the blower motor isn’t working right, the car ac fan slows down, goes faster and slower, or does not work.

3. Worn Out Motor:

A worn-out motor may find it hard to keep the fan going at the same speed, so the fan may speed up and slow down at random times. This can also make the air conditioner run loudly when turned on.

Worn Out Motor

Also Read: How Long Should Car AC Take To Get Cold

4. Inside Atmosphere:

Why does my car ac blow fast then slow? The fan speeds up, the car ac fan speed low and it can also be changed depending on how hot or cold it is inside the car. The fan motor is under additional strain if the automobile’s interior is sweltering since the air conditioner must work harder to chill the air.

Inside Atmosphere
source:pak wheels

5. Actuators:

Ac fan speed low or high? Actuators in modern cars control the fan’s speed and other parts of the AC system. If one of these motors doesn’t work right, the car ac blower fan running slow and can speed up in strange ways. The motor might be stuck in one place, making the fan work harder than it needs to.

source:NMB technologies

Also Read: Is It Ok To Leave Car Running With AC On

6. Faulty AC Control Module:

The AC control module controls the speed of the fan and the temperature. If the control module is broken, the car ac blows fast and then slow.

7. Low Refrigerant (Freon) Levels:

The fan will have to work harder to maintain the desired temperature in the room if there is insufficient refrigerant since the air conditioner won’t be able to chill the air effectively. The fan speeds up and slows down because of this.

Low Refrigerant Levels
source:complete car

8. Electrical Problems:

The fan can speed up and slow down because of electrical problems, like faulty wires or a broken alternator. The air conditioner’s failure to function may also result from these issues. So, the car ac fan goes up and down.

Also Read: Is It Bad To Have AC On With Windows Open In Car

How to Fix Car AC Fan Speed Issues?

If you’re experiencing issues with your car’s AC fan speed, addressing the problem is crucial for a comfortable driving experience. I’ve personally dealt with this and found effective solutions.

1. Check the Air Filters:

Reddit users said If the air filters are dirty or jammed, you should change them. Clean filters let more air flow through, which puts less stress on the fan motor and stops it from speeding up and slowing down.

Check the Air Filters
source:indian auto

2. Check the Blower Motor and AC Control Module:

If the motor for the blower is broken and the AC control module is faulty, it must be changed. A qualified mechanic should be the only one to perform this.

Also Read: A/C Fan Increase When Braking

3. Check the Refrigerant(Freon) Levels:

If the AC system is low on refrigerant, have it checked for leaks and filled with the right amount of refrigerant. This is also something a skilled mechanic should do.

 Check the Refrigerant (Freon) Levels
source:luce aircon

4. Check for Electrical Problems:

If you think electrical problems make the fan speed up and slow down, have a professional check out the electrical system. If there are any electrical issues, they will be able to identify them and resolve them.

Try putting some oil on the shaft of the motor to lubricate the bearings. But it is also possible the motor windings are shorting out. Then you would need to replace the motor.

5. Parking in Shade:

Your automobile’s interior cools down when you park it in the shade. This implies that less effort is required on the part of the fan motor and air conditioner to chill the air.

Parking in Shade

The problem with the actuator can be fixed by putting the car in the shade and sunshades on the windows to cool it down.

Also Read: AC Recharge Hose Won’t Fit

Does the blower motor slows down when accelerating?

Blower motor speeds up when accelerating? In many cars, the blower motor speeding up when you accelerate is considered normal. It occurs because HVAC systems in contemporary cars are frequently linked with the electronics and engine of the car.

Why is my car AC fan blowing slow?

Car AC Blower Fan Running Slow? Experiencing low airflow from the blower motor can be frustrating, often indicating a faulty blower motor resistor. This component regulates fan speed, so when it malfunctions, airflow diminishes, affecting both heating and cooling performance.

Car Ac Blows Fast Then Slow:

If your car battery is a bit tired, or you have an older car where the wiring is getting a bit tired, it is common for the fan speed to fluctuate as you rev the engine.

Air Conditioner Fan Speed Fluctuates:

Under auto mode, the AC’s compressor and fan adjust their timing and speed based on ambient conditions. This variability is a standard feature.

AC Slows Down When Car Accelerates:

In this scenario, a faulty blower motor and resistor are probable culprits, but it’s wise to inspect the charging system first. Ensure there’s no voltage drop causing fan slowdown. Visit a parts store for alternator load testing and battery check.

Car Air Conditioner Inconsistent:

Intermittent AC issues, cycling between cool and warm air, may stem from a clog in the system, compressor or compressor clutch failure, faulty condenser fan, or actuator malfunction directing airflow.

Oscillating Fan Speeds Up And Slows Down:

Fluctuating fan speed in your car’s AC system could result from a dirty or clogged filter, hindering airflow. Alternatively, a faulty fan motor or capacitor may cause speed variations.

How To Increase Car AC Blower Speed?

  • Turn on the AC: Ensure that the AC system in your car is turned on before altering the blower speed. To do this, hit the “AC” or “MAX AC” button on the control panel.
  • Adjust the fan Speed: Why ac fan speed is slow? Find the knob or buttons that control the fan speed and adjust it. Different fan symbols, numbers, or words like “Low,” “Medium,” “High,” or something similar may be used to indicate the settings. To raise the fan speed, turn the knob or press the buttons.
Source: your mechanic

1. What does a bad AC fan motor sound like?

If your air conditioner is screaming, the fan motor is broken. This sound could also come from a broken condenser system’s compressor motor.

2. How long do AC blower motors last?

It will most likely persist between ten and twenty years. When the AC motor breaks, it’s often time to consider changing the whole system. One reason they last so long is that they are made to stand up to temperatures up to 140 °F.

3. What causes an AC blower motor to go out?

A broken blower motor can stem from various factors, including aging, worn bearings, electrical issues, and dirt accumulation. Maintenance neglect often exacerbates these issues.

4. Why Does My Car Slow Down When I Turn On The AC?

When the AC compressor activates, it requires 5-10 horsepower to pump fluid, reducing the available power for propulsion. If your car has 100 horsepower, a portion is diverted to the AC, impacting speed.

5. Car AC condenser fan running slow?

Why my ac fan speed is slow? Weak airflow often results from a fan spinning at a sluggish pace. Ensure the fan is set to low speed if adjustable. If not, a failed capacitor or motor bearings in need of lubrication may be the cause.

6. Car AC Fan Not Working?

AC fans not working in car? Cooling fans may malfunction due to blown fuses, electrical shorts, or debris damage. Fortunately, replacements are straightforward, allowing your mechanic to swiftly restore functionality and get you back on track.

7. Does AC Stops Blowing At High Speeds?

If the AC fan’s spindle is damaged, it can restrict movement, leading to slower speeds or a shutdown, causing compressor overheating and AC shutdown.

8. Why is my AC fan surging?

The AC fan may surge due to compressor issues or loose parts like a wobbly fan blade. Indoor components, such as the motor blower or blower wheel, can also cause vibrating noises.

9. What does a bad AC fan motor sound like?

A screeching noise from your air conditioner suggests a problem with the fan motor or compressor. It may indicate a damaged blower fan motor indoors.

10. Why does my AC keep changing speeds?

In auto mode, AC adjusts fan speed for quick temperature control. If room temp is high, fan speeds up to cool faster.


In conclusion, car air conditioner fan speed fluctuates for several reasons, including clogged air filters, malfunctioning blower motors, inside atmosphere, faulty AC control modules, actuators, low refrigerant levels, and electrical problems. Regular maintenance of your car’s AC system, parking in the shade, using sunshades, and regularly cleaning the AC system can help prevent these issues.


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