Why Does My Ac Only Works When Driving?

Have you been in situations where you jump into your car, turn on the air conditioning system, expecting cool air only to get warm air? Now you hit the road, and the air conditioner starts working. But wait a minute, does my car ac only works when driving?

If this repeats several times, it shows your ac only works when driving. This can happen for several reasons. In this short post, I will explain the possible causes and how to track and fix the underlying problem. But first, let’s start with the probable causes.

car ac only works when driving

What Causes ac only works when driving?

The air conditioning system in cars consists of several components that work in harmony to provide cool air in your cabin. Any issue with any of these components will affect the overall air conditioner’s performance. Here are the potential causes why your ac only works when accelerating.

Damaged condenser fan

A damaged condenser fan is the most common cause of air conditioner that only works when driving. The condenser is like the radiator fan. It dissipates heat from the condenser while the engine is running, helping to reduce the refrigerant temperature as it runs through the condenser.

Car manufacturers typically design condenser fans to activate once the engine reaches 195 to 220 degrees Fahrenheit. If the fan does not turn on, it won’t reduce the refrigerant temperature as it runs through the condenser. So, it’s okay to ask why AC will work when driving fast since the condenser fan is damaged.

Here’s why. The condenser relies on the fan to dissipate heat when the car is not moving. But once the vehicle is in motion, the ambient air cools the refrigerant passing through the condenser. Since the fan is faulty, there’s no air to cool down the refrigerant moving through the condenser when the vehicle is stationary.

Low refrigerant levels

The air conditioning system is a closed-loop system. This means the refrigerant is supposed to stay within the system. It shouldn’t go anywhere. However, cracks may occur on the refrigerant lines or the condenser, leading to leakages in the system.

Plus, the ac condensers have a high risk of damage than other system parts since they sit in front of the vehicle. This is especially true when the car does not have under guard. Aside from that, the condenser tubes and seals can age off and cause leakages. However, it can take up to 10 years for this to happen.

Leakages will cause low refrigerant levels within the system. The air conditioning compressor will struggle to pump enough refrigerant to keep you cool in the cabin while the car is idling. But the ac will only work when driving slow or faster because the engine turns along with the ac compressor at a higher revolution per minute. Sometimes, it’ll cause heat, and ac only works when driving.

Clogged compressor or condenser

Since the ac is a closed-loop system, it is hard for junk, debris, and other contaminants to get inside it. This, however, does not mean the system cannot clog. Blockage often happens after replacing old parts with used ones or when internal parts of unit components are wearing off.

For example, if the internal parts of the compressor wear off, the debris will travel to other unit components along with the refrigerant. This will eventually block components like the condenser or the compressor itself. If this happens, the air conditioning system will struggle to circulate refrigerant.

The blockages may form a paste-like substance in the system. This will prevent adequate refrigerant circulation when idling, causing the ac to only work when driving fast.

Other faulty system components

Blockages will not only cause my car ac only works when driving fast. The contaminants may also damage other system components. And when a single unit is not working, it may affect another unit.

For instance, a broken wire in the clutch coil will prevent the compressor clutch from cycling. And if the clutch isn’t working, the compressor will not work. In such cases, the air conditioning system will not work whether you’re idling or driving.

As reiterated above, the condenser itself can develop issues over time, which could lead to cracks and refrigerant leaks. The Evaporator can become faulty as well. A defective evaporator can manifest itself in several ways.

First, it could cause leaks or blockages, which can cause the air conditioner to work only when driving fast. I published an article that explains how to clean ac evaporator without removing it. Check it out if you suspect the evaporator is clogged.

Overheating engine

Firstly, you need to understand that overheating engine does not directly affect the air conditioning system. However, the engine compartment temperature will rise if the car is overheating. This will invariably affect the ac system since they are located in the engine bay.

When an engine is overheating, the condenser fan may not be enough to dissipate the heat from the refrigerant traveling through the condenser, preventing the ac from working on idle. However, the ac may start working once you hit the road since the ambient air will help the condenser fan to cool the refrigerant.

You have seen the potential reasons why VW Jetta, Nissan Versa, Ford F150, or G37 ac only works when driving. Any of the issues described above can prevent the ac from working on idle on any car model. With that in mind, let’s see how to fix a car ac that only works when driving.

How does fixing ac only works when driving?

There will be more than one feasible solution to this problem since several possible causes exist. Firstly, you need to diagnose the system to detect what’s happening within the ac unit.

my ac only works when driving

Repair system leakages

System leakages are one of the most common causes of this problem. Therefore, check if there is leakage on any of the ac system components. Check the seals around the ac units and ensure they are in good condition. If there are any loose seals, tighten or replace them as needed.

Examine the refrigerant lines, the condenser, the expansion valves, and the compressor, and ensure there’s no leak anywhere. If you detect any leaks, patch them with sealant or repair them accordingly.

Recharge the ac unit

Check the ac refrigerant in the system and ensure it is okay. If you finish repairing the leaks or find low refrigerant, you must recharge it with the recommended refrigerant. I published a well-detailed article on how to recharge ac refrigerant. Follow the simplified guide in that article to recharge your ac system.

Check and fix the condenser fan.

Inspect the condenser and ensure it is working correctly. If the fan is not blowing, track the cause and fix it. This could be all you need to rectify the underlying problem.

Check and clean the cabin filter.

Locate and inspect the cabin air filter. Usually, a clogged cabin filter should prevent adequate airflow when idling and driving. But don’t rule it out. It could be the culprit in this case, especially if the compressor is weak.

Inspect and repair compressor clutch issues

Turn on the ac and examine the clutch to see if it engages properly. Listen to a grinding or whining noise from the clutch. A damaged clutch will cause AC not to blow cold air. To fix clutch issues, check the electrical wires and connectors to ensure they are adequately secured and free of corrosion.

Clean the clutch with a toothbrush to remove the debris on it. Check the oil and top up as needed. Also, if the clutch is not spinning, disassemble it to find out what is wrong. You may need to replace it.

Examine the compressor and condenser

Inspect the compressor and condenser and ensure they are not clogged. If any of these system components is clogged, it’ll prevent the ac from working on idle or stop it from working at all.

Fix overheating issues

Check the temperature needle on the instrument cluster and ensure it is in the middle of the gauge. Next, check for other signs of overheating. After that, diagnose and resolve the root cause of the engine overheating.

Contact an experienced HVAC technician.

If you don’t have HVAC experience, you can only recharge the system, fix minor leaks, and proffer feasible solutions to other minor problems. However, if the problem persists, contact an experienced HVAC technician to thoroughly diagnose and resolve the underlying issues.

Sometimes, the system may leak, and you cannot access it unless you know your onions. Also, there could be minor issues that require the technical experience.

Frequently Asked Questions – FAQs

Q: Why is my car AC cold only when driving?

The air conditioning system in your car should be blowing cold air when idling and driving. Suppose the ac stops blowing cold air when idling. In that case, you likely have issues like blockages in the system components, a faulty condenser fan, a clogged cabin air filter, a clogged condenser or compressor, or low refrigerant levels. You must track and rectify the leading cause before you can start receiving cool air when idling.

Q: Why does the AC in my car work better when I’m driving?

Whether your car ac only blows cold air when driving or works better when driving, it shows something is wrong with the system. It could mean you have a defective condenser fan, a clogged compressor or condenser, blockages in the system, low refrigerant levels, or a clogged cabin air filter.

At first, the ac will work better when driving. But as the problem expands, the ac will only work when driving. Finally, depending on the severity of the problem, the ac unit may stop working completely as you drive for an extended period.

Q: How much does it cost to fix ac that only works when driving?

It is impossible to estimate the exact amount to repair ac that only works when driving because several factors can be the leading cause. In essence, the repair cost depends on what’s wrong with the system.

For instance, if a faulty compressor is the root cause, then you should budget between $200 and $800, depending on your vehicle type. Likewise, if a lousy condenser is the root cause, it’ll cause between $300 and $500 to replace it; however, if the leading cause is a clogged cabin filter or low refrigerant level, budget to spend $20 to $50 to replace the filter and $100 to $200 to get a professional ac recharge.

Final Words

Several factors can be the culprit if your ac only works when driving. It could be a clogged air filter that needs replacement, low refrigerant levels that needs a recharge, a faulty condenser fan, blockages within the system, a clogged condenser, or a lousy compressor.

If you’re experiencing this issue, follow the above guides to fix it. Contact an HVAC expert if you are unfamiliar with the cooling system working principles.

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.

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