Air Conditioner Only Works When Car Is Moving – What’s Wrong?

A car's air conditioner creates a comfortable environment for both drivers and passengers. As a car owner, you may be wondering what is wrong when the AC only works while your car is in motion. Fortunately, we have consulted experts in this field, and here is what they have to say. 

Failure of some components can make an air conditioner function only while a car is moving. The following are possible causes of the problem:

  • Faulty condenser fans.
  •  Low refrigerant charge.
  • Bad compressor clutch.
  • Dirty/clogged compressor.

To prevent this problem, make sure to maintain your car correctly. Keep reading to get detailed information on issues that may cause a car's AC to work only during movement.

Female hand checking air conditioning panel inside car, Air Conditioner Only Works When Car Is Moving - What's Wrong?

Why Air Conditioner Only Works When A Car Is Moving

Woman hand on air conditioner ventilation grille in car. Climate control panel

Whenever you notice that your air conditioner only functions when you start driving, you should check some of the vehicle's components to find the source of the issue. One of the following could be the cause of the problem:

Faulty Condenser Fans

The condenser fans in vehicles transfer heat from the refrigerant system to the outdoor air. When the heat transfers out of the condenser, it moves to the expansion valve before going into the evaporator coil. When the fan goes wrong, your AC may only work when you start driving.

The primary purpose of the condenser fan is to reduce the refrigerant's temperature and rotate when the engine reaches a temperature of about 195°F - 220°F. If the fan fails to turn, you should check the fuses and relays of the condenser fan. Also, check loose connections and short circuits.

Low Refrigerant Charge

Manufacturers use a low-pressure switch to stop the compressor from operating when the system's refrigerant is low. However, an air conditioner's compressor may need a regular oil supply to prevent failure.

To solve problems caused by a low resistance charge, you must start the engine, roll down all windows, and turn on the air conditioner. When the engine settles down, set the blower speed to two and give the engine about 10 minutes to get to its highest operating temperatures. 

Make sure to check the AC pipe for moisture and take note of the temperature. The pipe should be cold, and the condensed water should be visible. Also, check the pipe beside the firewall. If it is cold, the possibility of low gas volume might have caused it. 

Bad Compressor Clutch

The purpose of the compressor clutch is to engage the compressor shaft. When the compressor clutch is not working, it will be difficult for the air conditioner compressor to pump refrigerant. 

To find out if the compressor clutch is working, you should turn the vehicle AC to MAX and start the engine. Then observe the pulley and the clutch as they are expected to spin the same way at this stage. If only one is rotating, the system has a fault.

The pulley and clutch may not be spinning uniformly due to an open circuit, blown fuses, poor ground, or bad clutch coil. You can use a multimeter to find the faulty components and replace them. 

Dirty/Clogged Compressor

The compressor is responsible for circulating refrigerant in the system under pressure, from the evaporator to the condenser coils. A dirty or clogged compressor can cause an AC to function only when a car is moving.

To find out if the compressor is dirty, you can do a visual check of the AC line, compressor, and condenser. You are more likely to see accumulated dust due to oil sedimentation. You should also check the AC filter to see if it is blocked.

You can use a pressure washer to wash the condenser through the bumper openings. Be careful not to set the pressure washer over the condenser as it may damage it. 

man hand turning on car air conditioning system

How Do I Know If My AC Compressor Is Bad?

When the compressor has an issue, it can cause the AC to function only when a car is moving. If you notice the following signs, then your AC compressor is going bad:

Strange Sounds

When you hear strange sounds after turning on your AC, and the sound stops when you turn it off, there may be something wrong with your compressor.

AC Blowing Hot Air

You turn on the AC to get cold air, especially on sunny days. If your AC blows hot air, it could mean that your compressor is going bad. An AC can also blow hot when the refrigerant is low. The hot air is like a warning before the compressor stops working.

Seized Clutch 

The compressor of an air conditioner has a clutch connected to the engine of the car to draw power. The power is used only when the compressor needs it. If the pulley or clutch is stuck, the compressor will not work because it won't be able to get power. The clutch can't be replaced if it gets stuck. The only option is to change the compressor.

How Do I Know I Have A Faulty Condenser?

The AC in a car has several components, including a condenser, compressor, and evaporator. Any of these components can fail or be affected by blockages. Clogs in an AC can cause some parts to function poorly. Here are some signs that indicate that you have a blocked or faulty condenser: 

  • Automatic shut-off: If you notice that the compressor is cycling on and off, it could be traced to the feature that detects lower pressure in the system. Low system pressure is caused by air or contaminants in the condenser. 
  • Compressor freeze: This means that dirty lubricant has jammed the compressor. You can try turning the outer part of the clutch manually to see if it rotates.
  • Intermittent cooling prompts the flow of cool and warm air from the vents. When air and moisture combine, they can form ice that blocks the condenser. 

Why Does My AC Get Stronger When I Accelerate?

It is normal for a vehicle's AC to get stronger during acceleration. This is because the alternator increases the battery voltage, which in turn boosts the fan voltage, making them run faster. 

Closeup of hand driver man checking adjusting air from conditioning the cooling system with flow of cold air in car. Leave space for writing text.

Why Does My AC Get Hot At Idle?

This happens at some point in most vehicles, and the leading cause of this problem is poor maintenance. The following are the possible reasons why your AC gets hot at idle:

Blocked Condenser

The condenser in a car AC compresses the refrigerant. It can be found in front of the car, so the debris gets trapped there easily. When the debris blocks the condenser, it fails to compress the refrigerant. Hot refrigerant can't blow cold air when idle.

Low Refrigerant

The cold air that comes out of the AC is the refrigerant gas. So if the gas starts to leak, the air conditioner won't be able to blow cold air.

Why Does My AC Start Blowing Warm After Driving For A While?

Driver hand tuning air ventilation grille, fresh air is coming out

As a car owner, you may have noticed that your AC blows warm after driving for some time. This could be a result of the following:

Refrigerant Leak 

An AC can start blowing warm when there is the refrigerant is leaking. This happens when refrigerant and moisture mix, forming ice in the system.

Blown Fuses

Your car's AC system comprises wires, fuses, and switches. Usually, these three work together to provide cold air. But if one of them fails, your AC may start blowing warm air. 

Faulty Compressor Clutch

The compressor clutch plays a significant role in keeping your car cool. If the compressor clutch is faulty, your vehicle's AC will keep blowing warm air, as a damaged compressor cannot properly compress refrigerant into the air conditioning system to give off cool air.

How Do I Maintain A Car AC?

Closeup female hand adjusting air ventilation grille

Maintaining your car's AC is recommended so it can function correctly. Here are some things you can do to keep your AC in working order:

  • Run the AC at least once a week for about 10 minutes: This is needed to maintain the gas pressure to keep the compressor working perfectly.
  • Run the defrost mode for 10 minutes: This is done to eliminate excessive moisture that can cause odors in your car.
  • Recharge: Make sure to recharge your AC every two years.
  • Clean the air filter often.

To Wrap Up

Various problems can be avoided when an AC in a vehicle is maintained correctly. You can detect potential issues that may cause an air conditioner to function only when the car is moving, saving yourself time and money.

If you enjoyed reading this post, here are similar articles you may like:

How To Bleed Off An Overcharged Car AC?

Why Does My Car Air Conditioner Only Work On High?

Share this article

Leave a Reply

Your email address will not be published. Required fields are marked *