Car AC Cold Only When Driving? [Here’s Why And How to Fix!]

If you live in a hotter environment, your car air conditioning system is a lifesaver. Unfortunately, air conditioning systems don’t always work right, and they don’t care whether or not it’s mid-summer.

One of the most common problems you’ll face with your car’s air conditioner is the system only works when you’re actually driving. 

Some of the most common reasons a car air conditioner may only be cold when driving is because of a broken condenser fan, a blockage in the condenser, or low coolant levels.

Let’s look at what happens when each of these things goes wrong and what you can do to help fix the problem at hand. 

1. The Air Conditioner Condenser Fan Isn’t Coming On

In case you can’t tell, based on all of our potential problems being related to condensers, they are the main part of the air conditioning system. Unfortunately, various parts of the condenser system often go wrong, and the condenser fan is one of the most significant problems you can face with this system.  

The number one sign you’ll notice if you’re having a problem with your condenser fan is that the car will only cool when driving at highway speeds. The condenser fan brings heat from the inside part of the vehicle to the outside.

If you’re traveling at a higher speed, often, the condenser fan won’t need to do any real work because there will already be a lot of air circulating through the system. 

Another thing you’ll notice is that the car begins to overheat when it is idling. Often, you can help pull heat out of the engine by running the heater on full blast while idling, but I can tell you from experience that this is downright terrible in the middle of summer. 

You may also begin to notice the air conditioner has a burning smell when you turn it on. If you smell burning while running the air conditioner, you’ll want to avoid driving your vehicle and take it to a mechanic’s shop.

This can be dangerous because it usually means that the other components of your air conditioning unit are beginning to burn. 

Causes and Solutions

One of the primary reasons your condenser fan may suddenly be having problems is because of a blown fuse. This isn’t always the first thing that comes to mind, particularly when you’re sweltering in the heat, but make sure you consider this because it’s probably the easiest fix. 

If you think this may be an issue, you’ll want to find your car breaker box, usually located underneath the steering wheel on the left side of the vehicle, and look for any flipped breakers.

You’ll know that the breaker has been flipped if it’s going in the opposite direction than all the rest. You may also need to replace the fuse, a fairly simple process.

You may also find the temperature sensor isn’t working quite right, which is prohibiting the condenser fan from kicking on. One way to test this is by placing a jumper wire across the connector and observing whether or not the fan turns on. If it does, then it’s likely your temperature sensor. 

Lastly, if you hear noises from the fan, the problem is likely with the fan itself. If you hear any grinding or scraping when you attempt to turn on your air conditioner, it’s time to take your car to the mechanic. 

2. You Have a Blockage in the Condenser

Most people don’t take the time to clean some critical parts of their vehicles, including the condenser. If you suddenly find that your car’s air conditioner isn’t working quite right and you’ve already checked out the fan, I would look at blockages in the condenser next. 

Often, condensers become clogged with dirt, preventing air from properly circulating throughout the system. It’s best to take care of this problem sooner rather than later. Otherwise, you’ll end up needing to replace your entire air conditioning system eventually. 

Causes and Solutions

We’ve already talked about the cause for the most part. Over time and with usage, anything collects dirt, and since your car operates outdoors, it’s always exposed to a lot of dirt.

When driving, especially if you’re using your air conditioner, the dirt gets sucked in along with the air and eventually builds up in the coils. 

So let’s talk about how you can clean your condenser. 

1. Start with a cool engine. This should be a no-brainer, but sometimes you don’t think about it. Give your car plenty of time to cool down before doing any work. Ideally, you should let it cool overnight to be sure no parts are still hot. 
   
2. Remove the front bumper. If you aren’t sure how this works, you can read your car’s owner’s manual or look up a quick video on YouTube.
   
3. Be sure to protect the condenser with plastic. There are some parts you’ll want to keep dry, so be sure to cover these sensitive areas with some plastic. You can tape it down to get it to stay. 
   
4. Begin removing dirt with a shop vac or brush. This process will remove the majority of the dirt. 
   
5. Apply coil cleaner and allow it to sit for about 5 minutes. You can grab coil cleaner at any of your local automotive shops. 
   
6. Rinse with a hose or spray bottle. Make sure to allow the condenser to dry before putting everything back together.
   
7. Put the front bumper back on. Once everything has had the time to dry, ensure you place your front bumper back on very securely. 

3. Your Coolant Levels Have Gotten Too Low

Your car uses coolant, also known as Freon, to keep your air conditioner running smoothly and operating with nice cold air.

Over time, however, those levels drop, and usually, you end up with an air conditioner that will only produce cold air while driving. Sometimes it doesn’t even do that if the coolant levels are really low. 

Usually, if coolant levels are dropping dramatically, it’s due to a leak in the condenser itself. The components within the condenser are very prone to wear and tear and will often form holes over time. 

Causes and Solutions

As I discussed, rapidly falling coolant levels are usually due to a leak in the condenser itself. So what’s the answer? 

If your coolant levels have decreased over time, you can simply add coolant to the vehicle, and you should be good to go. Sometimes if your car only has a small leak, you can still add coolant and it shouldn’t leak out for a while. 

If you have a major leak in your condenser, the best thing to do is take your car to a professional. Condenser leaks can be difficult to fix, and if you aren’t sure what you’re doing, you might cause more harm to the vehicle. 

One Other Thing to Consider

Sometimes the air conditioner isn’t working right because it’s simply been too long since you serviced it. While air conditioners don’t need regular checkups like brakes or oil changes, they do need to be recharged at times.

Recharging the air conditioning system looks like doing a full maintenance inspection and replacing all your fluid levels, including coolant. For more information about this process, check out my other blog on how often to charge your car’s AC.