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DISCLAIMER: AS AN AMAZON ASSOCIATE I EARN FROM QUALIFYING PURCHASES. THIS POST CONTAINS AFFILIATE LINKS THAT WILL REWARD ME MONETARILY OR OTHERWISE WHEN YOU USE THEM TO MAKE QUALIFYING PURCHASES. FOR MORE INFORMATION, PLEASE READ MY EARNINGS DISCLAIMER.

Running the air conditioner adds to the engine’s mechanical strain. This added load increases the heat load produced by the engine. At the same time, this heat load must be shed into the atmosphere by the radiator in order to keep the coolant temperature under control.

If your automobile overheats when the air conditioner is turned ON, it’s likely that the cooling system or engine is malfunctioning. A slight increase in engine temperature is to be expected when you turn on A/C, but a significant increase in engine temperature indicates a lack of coolant or a problem with the water pump.

When you first switch on your vehicle, the air conditioning after a long day of parking in the heat will blow hot air. This is because cool A/C air is trying to move through the hot ductwork of your vehicle.

The car’s air conditioner also marginally increases engine load, resulting in an increase in heat production. Here is a list of problems that could contribute to your car running hot with A/C being ON:

  1. You have a cooling fan problem
  2. Your cooling system is clogged, dirty, or needs to be bled.
  3. Your compressor just quit on you!

Now, let’s dive into detail:

Broken cooling fan or fans

It is a very common problem in cars and if the cooling fans are malfunctioning, your car will be overheating once the air conditioner starts working. The majority of new vehicles today usually have two electric radiator cooling fans.

Since the air conditioner adds to the engine’s workload, when the coolant temperature exceeds a specific degree, one of the fans will come ON. This usually happens when you get good airflow through the radiator, in situations where you are stuck in traffic, for example.

The other fan will turn ON when the compressor starts running and if it doesn’t, your engine could start overheating. If the second fan fails (or the power relay, that is used to turn ON the second fan, has failed), your engine will not be able to keep up with increased engine heat load.

It could also be the result of a combination of two or more problems. If you have a defective A/C electric fan, along with a neglected cooling system, the result could be disastrous for your engine.

Single cooling fan

Many vehicles on the road right now have only one cooling fan for both the condenser and radiator cores, electrical or mechanical. The speed of the fan is something you may want to pay attention to and the common problem with a dual-speed electric fan is:

When the A/C is turned ON, the extremely hot air from the condenser will be too much for a single fan to handle at low speed.

If the car only has only one single-speed electric fan and it works properly, the only reason that your car is overheating while turning ON your air conditioner would be:

You have a partially clogged cooling system that can’t handle the increased heat from the A/C condenser.

If you have a mechanical fan (which is connected to the engine’s water pump and rotated by the drive belt), then you should not overlook a fan clutch. This fan is operational depending on whether cooling is required or not.

Increasing the load on the engine will engage the clutch and allow the fan to be powered by the engine to move air for cooling down the engine. If the clutch fails, you will have an overheating problem.

The most straightforward way to determine whether you have a fan is the issue is paying attention when your overheating starts. If it starts in slow traffic or idling, then it is highly likely that you have a cooling fan issue.

If this is the case, it is time to visit your mechanic to check out cooling fans, fan motors, or the whole electrical connection.

Dual cooling fans

If your car has two electric cooling fans (one for the A/C condenser and the other one for the radiator, then check if they are both working properly.

Radiator and cooling system

A radiator is a set of fins behind the automobile grille. It is part of the car cooling system and its jot job is to pull heat away from your car and into the fins. This is how your engine stays cool.

Since the condenser lies in front of the radiator, if the radiator becomes blocked and inefficient, and the extra heat that is coming from the A/C condenser will overload the system. If your cooling fans are working properly but the car still overheats when idling, the radiator could be the source of the problem.

With time, the radiator grille can become clogged with dirt and corrosion, or something can get sucked in into it which could cause the airflow abstraction. If your radiator can no longer able handle the additional heat load supplied by the A/C system, and the engine overheats.

To solve this issue, look through the grille and if you see anything that is restricting the airflow, remove it. You may discover that the radiator is broken or too old and this is what is giving you problems with overheating.

An insufficient amount of coolant and a problem with a water pump (that moves it through tubes) could also lead to an overheated engine. A water pump is an important component of the cooling system in your car, as its primary function is to circulate coolant from the radiator to the engine block.

Very important point! The engine’s coolant has a shelf life and this is why the radiator can become filthy and clogged. Coolant can serve you for a long period of time, but it requires regular changes to keep your radiator clean.

Flushing the radiator, as a regular part of your car maintenance program, is also required to keep the system in good working order.

Air in the cooling system

Most cars on the road right now have pressurized cooling systems that use the closed circuit of hoses to move coolant around the engine. When air enters this sealed system, air pockets can form, causing clogs and bubbling.

If your cooling system has formed air pockets, your coolant flow is not consistent and the engine will start to overheat. This commonly happens after a coolant refill or flush.

What to do? After flushing, you need to bleed any excess air from the radiator and cooling system by running the engine for about 15 minutes with the pressure cap OFF.

Low pressure in the tubes

If the cooling system’s pressure is compromised by a leak, blown head gasket, or faulty pressure cap, the boiling point of the coolant will fall as the pressure inside the system drops. This will cause coolant to boil inside the system and the car will overheat.

What to do? In the case of a blown head gasket, the pressurized air from the cylinders enters the cooling system quickly, and that will cause the reservoir to bubble along with antifreeze seeping into the cylinder head.

All the leaks must be inspected by a specialist and fixed in a timely manner. A faulty pressure cap needs to be replaced before more damage is done to a radiator.

A/C compressor has seen better days

This is one of the most common causes of AC overheating and is especially true if the car only overheats while the air conditioner is switched ON.  An air conditioner compressor will put an additional strain on the motor engine if the pulley is worn out or bearings are damaged.

In this case, the engine will be working harder and overheating may result. The compressor itself could also be old and “out of shape”, which means that it is time to replace it.

If your engine runs normally with A/C being OFF but overheats when the engine is turned ON (while fans are working and the radiator is clean) then ask your mechanic to check out a compressor issue.

Here is a GM compatible compressor (paid link) and yes, more compressors are conveniently sold on Amazon:

Hope this helps to solve your problem.

 

This article is for informational purposes ONLY and is NOT a replacement for professional advice!


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