Car Overheats When AC Is On – How to Fix

When the sun beats down on a hot summer’s day, drivers worldwide are thankful for their car’s air conditioning (AC) systems. The press of a button. The twist of a dial. That’s all it takes to create a cool, refreshing cabin, helping you escape the heat and feel fresh, even at the height of summer.

Unfortunately, AC units can have negative side effects. Some drivers have even noticed their cars overheating when they activate the AC. In this guide, we’ll look at why that happens and how to fix it.


How to Know When Your Car Is Overheating

Before we dig into causes of AC-related overheating, it’s important for drivers to know how to spot this problem in the first place. So, let’s dig deeper into some of the most common symptoms of an overheating vehicle:

  • It Feels Hot: Obviously, an overheating car will feel hot to the touch and excessively hot inside, even with the AC active.
  • The Engine May Shut Down: In the worst cases, an overly hot engine may fail to start or suddenly stop while you’re on the road.
  • High Temperature Gauge Reading: Keep an eye on your dashboard’s temperature gauge. If it gets too high, that’s a clear sign that the engine is excessively hot.
  • Strange Sounds: You may hear odd ticking or knocking sounds from the engine area if your car’s overheating.
  • Burning Smells: Along with weird sounds, drivers may also notice unpleasant smells, like burning, if the engine is too hot.
  • Steam: An obvious sign of an overheating engine is when you see steam coming out from under the hood.
  • Sluggish Performance: You might also notice your car struggling to accelerate or maintain high speeds.

Reasons Why Car Overheats When AC Is On

There are lots of reasons behind overheating engines. It’s not always connected to the AC. However, if you notice that the overheating symptoms only seem to appear – or are more prevalent – with the AC active, there’s likely to be a connection. Here’s why.

A Faulty Compressor

The compressor is, in many ways, the beating heart of the AC system. It pressurizes the liquid refrigerant to cool down the car’s interior. However, it has to draw some energy from the engine to do so.

If it isn’t working as it should, it may leech more energy than necessary, putting a huge strain on the engine. Under that kind of pressure, engines are bound to overheat.

Problems with the Fan

Fans are also critical components of the AC system. Powered by their own dedicated motors, they spin to propel air into the cabin or over the engine to cool it down. However, a problem with a fan motor, switch, or the blades themselves can all cause the fans to work incorrectly.

There may also be blockages preventing air from flowing where it should. If that happens, the fans may struggle to cool the engine or fail to turn on at all. Without active, reliable fans, overheating is inevitable.

Blocked or Dirty Condenser Fins

Yet another crucial piece of the AC puzzle is the condenser. This is the part that receives high-pressure refrigerant gas from the compressor. There, the refrigerant loses heat and changes back to liquid form, before flowing onward to the evaporator.

The condenser is made up of lots of little “fins” that help to extend its surface area and make it as effective as possible. But dirt, dust, and grime builds up on and around those fins. This negatively impacts the condenser’s efficiency, which can also contribute to engine heating.

A Malfunctioning Water Pump

The water pump controls the flow of coolant and water through the radiator, keeping the engine nice and cool. But if that pump isn’t operating correctly, nothing will cool down. The cabin will get hot, the AC will fail to have any impact, and the engine will heat up too.

Broken or Damaged Coolant Sensor

Last but not least, AC-related overheating can also be linked with coolant sensor problems. The coolant sensor tracks the engine temperature and essentially lets the car know when it needs to turn on the cooling fans.

If the sensor isn’t tracking the temperature properly, it won’t send the right signals. As a result, the engine can reach extremely high, potentially dangerous temperatures.

How to Fix the Problem

Car Overheats When AC Is On - How to Fix 1

We’ve seen why it happens, now let’s look at what you can do about it. Here are some simple DIY solutions you can try at home to resolve your AC overheating issues.

Inspect the System

First and foremost, take a look under the hood. Inspect the radiator, fans, and other related components. Look for obvious problem signs, like kinks in the radiator hose or rust and damage on the radiator. This can help you figure out exactly what’s causing the overheating in the first place.

Top Up the Coolant

If your car is low on coolant, it will naturally struggle to stay cool. Check the coolant level in the reservoir and fill it up if it’s running low. Additionally, you should change your coolant entirely every couple of years.

Replace or Repair Damaged Parts

Upon inspection of your AC components and cooling system, you may find that one or more parts are damaged. You’ll need to repair or possibly replace these damaged parts to prevent any worsening of the issue. Some repairs can be done solo. For others, it’s best to let the pros handle it.

Check and Refill Freon

The Freon, or refrigerant fluid, of the AC may also be running low. With the engine cool, use an appropriate gauge to check the levels. If the pressure and level of fluid is low, top up with some additional refrigerant to recharge the system.

Flush the System

Old or dirty coolant fluid could also be impacting your AC and causing your engine to overheat. If so, you’ll want to flush it out and refill the system with clean fluid. To do so, remove the coolant reservoir cap and open the drain valve to drain it out. Pour in a cleaning flush solution to clean the inside of the radiator, and follow the instructions on the container to complete the process.

If All Else Fails, Contact the Pros

These quick fixes might be enough to solve your AC overheating issue. But there’s also a chance that the problems may persist. If so, don’t delay – call in the pros. They’ll be able to carry out more advanced diagnostics and repairs to optimize your AC and prevent any further damage.

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