Car Overheats When AC is On

The good feeling that you get when a blast of cool air on a hot summer afternoons hits your body as you drive down the highway is second to none. But what happens when your air conditioner malfunctions and releases both cold and warm air in alternating sequence?

It is a huge inconvenience when your car air conditioner is not consistent in blowing cool air. You need to get to the bottom of this problem soon and restore your car’s AC to normal functioning. To do this, you have to understand the causes of this problem, how to troubleshoot and repair it.

How Does a Car Air Conditioning System Work?

Your car’s AC works like your home or office air conditioning system. The car air conditioner has different components working together to achieve its end goal. These components are the compressor, condenser, evaporator, receiver, refrigerant, and expansion valve.

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The compressor pressurizes the refrigerant and turns it from gaseous state to liquid. This liquid then circulates through a chain of tubes situated in the condenser. By doing this, the air flowing from outside into the vehicle comes to contact with the refrigerant. A temperature gradient exists between the fresh air and the liquid because of the condenser’s higher temperature liquid. In essence, heat transfers from the liquid into the air.

The refrigerant, on the other hand, moves into the receiver driver or the accumulator. A desiccant eliminates moisture in the refrigerant, thus creating a consistent supply of cooler refrigerant without compromising the air conditioning system’s integrity.

The cold refrigerant liquid then flows to the expansion valve or the orifice tube, which reduces fluid pressure and allows it to flow into the evaporator with ease. The cold refrigerant then moves via the evaporator. Air flowing from the passenger area is drawn into the evaporator and blown through the AC’s evaporator core. Given that the refrigerant is cooler, warm air flows into the refrigerant. Therefore, while warm air goes into the evaporator, cold air flows out of it.

The AC fan helps the cold airflow from the evaporator through the vents into the cabin, thus cooling everyone. Apart from cooling the cabin, this process also reduces moisture in the air by making the air drier. The AC system accumulates the condensate and drains it out of the car. Given that the refrigerant is now hotter, it converts into a gaseous state.

The low pressure fairly hot gaseous refrigerant moves back to the AC’s compressor to start the cooling process again. The cycle continues in a never-ending loop unless your car air conditioning system breaks down.

What Causes Your Car Air Conditioner to Blow Cold then Warm

Your car air conditioner blows cold then warm for many reasons, all of which indicate a faulty car AC system. These reasons are:

Low Car AC Charge Causing Evaporator Freeze Up and Low Airflow

When the system charge is low, it forces the evaporator coil to become very cold to the point of freezing the condensation occurring on the fins or the evaporator. The ice builds over time to the point of blocking the airflow. Your car AC system will then switch off is a compressor, which causes warm, humid air to flow into the cabin instead of cool air.

This happens because when the liquid refrigerant flows into the evaporator, it absorbs heat from the cabin air that flows over the coil. The heat from the cabin forces the liquid refrigerant to boil and turn into gas. In the process, the heat is removed from your cabin, thus making the car feel cool.

The right amount of refrigerant charge will ensure the evaporator maintains a steady temperature slightly over the freezing temperature. It will also ensure that the evaporator releases a steady air temperature of 40°F. When the refrigerant changes from a liquid state to a gas, it should achieve a maximum temperature of 50°F and flow out through the evaporator into the accumulator or the compressor to complete its cycle.

When a system is has a low charge, the gas refrigerant stays longer in the evaporator. It, therefore, removes more heat found in the cabin air flowing over the coil. The refrigerant fluid exiting the evaporator is overheated by over 10°F. The extra heat that the refrigerant absorbed from the cabin air causes the evaporator’s temperature to dip below the freezing point. In turn, the humidity found within the cabin air freezes on the surface of the evaporator. After a while, the ice formed from the moisture in the air builds up to the point of blocking the airflow across the evaporator, which turns off the AC and stops cooling air from flowing to you.

A Leak in the AC System

A small leak of the refrigerant is the most popular reason why a car’s air conditioning system slowly loses its cool. The leak usually arises from corrosion by the mixture of refrigerant and moisture. When the two combine, it results in a corrosive acid that destroys seals, hoses, and valves in the air conditioning system. When there is a leak, your air conditioning system, your air conditioning unit, could blow warm air because it lacks sufficient refrigerant within the system for cooling everything down.

If there is acid corrosion, the inside part of your air conditioning unit, such as the air compressor, is likely to be damaged. It may spread harmful fragments of metals all over your air conditioning system, which causes extreme damage, component failure, and damage to your air conditioning unit.

Electrical Issue

Your car is made up of interconnected wires, relays, fuses, and switches that allow it to function properly. In ideal situations, these different parts work in harmony to supply electric power to your car’s air conditioning unit that cools you. If anyone of these parts does not perform its functions well, your air conditioning’s ability to deliver cool air consistently will be affected. In most cases, the AC shuts and begins to blow warm air into the cabin. Even though this is meant to stop the possibility of fire breakouts, a single faulty fuse will cause a failure in your car’s entire air conditioning system.

Broken Compressor Clutch

Your car’s air compressor clutch is among the essential components of your vehicle’s AC system. It compresses the air conditioning system and maintains a steady flow of the refrigerant, which allows every component of the AC to work properly. Due to its continuous working process, the AC clutch is prone to wear and tear. This happens each time that you use the air conditioning unit to supply cool air to your car.

A faulty compressor will not sustain a consistent flow of cool air for a long period. A worn-out, failing, or damaged air compressor cannot control the flow of refrigerant into the air conditioning system to supply the cool air into your cabin.

Clogged Cabin Air Filter

A clogged cabin filter has the same effect on the evaporator as the low refrigerant charge. A clogged cabin air filter (view on Amazon) causes the refrigerant to eliminate too much heat, resulting in the freezing of the evaporator. Check the condition of your cabin air filter once you notice that your evaporator has frozen. Clean the air filter by removing debris and all the other clog forms that might be blocking the air filter.

Failing Expansion Valve

If your expansion valve is failing, there is a very high likelihood of your air conditioning unit to switch from cold to hot repeatedly. The work of the air conditioner’s expansion valve is to distribute the right amounts of refrigerant to the evaporator. However, if it is blocked, it restricts the flow of refrigerant. It could also allow the excess flow of refrigerant.

The slightest form of refrigerant restriction causes the hardware to become extremely cold. It can be very cold to the point where frost builds on the outer part of the hardware. Ice build-up also makes the air conditioning unit’s operation even worse from the inside, thus forcing your air conditioner o blow warm air.

An unregulated flow of refrigerant, popularly known as flooded refrigerant, to the evaporator, does not yield cooler air. Instead, the flooded evaporator leads to the supply of warmer air into the cabin by the AC.

When your system tries to regain control over the expansion valve, the rate of refrigerant flow will normalize, and you will notice the temperature of air beginning to cool once more. If you notice puddles of water below your car, you should inform your technician because this may be an indicator of frosting.

Poor Maintainance – Failing to maintain your AC can result in the AC failing and having problems. You need to make sure that the components that allow the AC to function are being looked after unless they can start to fail overtime. This can cost a lot to repair so it’s best that you prevent this from happening.

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How Do You Overcome These Problems?

Even though the problems named above are likely to increase, they can also be solved. As the car owner, you should be able to perform some corrective processes and repairs that will restore your car’s AC back to normal. Here are some of the solutions that you can implement to correct a faulty air conditioning unit.

Carry out regular inspections of your air compressor to avoid ending up with a broken air conditioning unit. Most air conditioners break down because of the worn-out compressor. Regular checks and maintenance will ensure that the compressor is in its perfect working condition at all times.

Your air conditioning unit may produce some strange sound indicating a fault in your AC’s expansion valve. When you fix the expansion valve annually, you will be able to have an air conditioning system that works at its optimum. Therefore, always visit your mechanic every time you hear your air conditioning unit making strange sounds.

Inspect your car’s air cabin regularly. Sometimes, during a long trip, your AC may blow air with a foul smell or high moisture content. Replace the cabin air filter as soon as possible.

When your air conditioner starts and stops, it may be as a result of the pressure sensor or the ejection of relays on your system. It is also important to inspect your AC switches properly because they may not be getting enough power from relays or fuses attached to the system.

Take your car to your local mechanic as often as possible. Regular inspection of your car means fewer problems with the car and a high-quality driving experience for you. Sometimes when a small problem is left unchecked, it may lead to a bigger issue that is not good for your car.

When your car air conditioner blows cold then warm, you should not be surprised. It could be one of the many reasons mentioned above. Luckily, there is a remedy to all of these problems. Always fix the issue within the shortest time possible. Involve your mechanic in areas beyond your scope. Most importantly, do not dismiss a small issue. Instead find a solution for the problem.