The car’s air conditioning allows the driver to control the temperature of the car’s interior. On the other hand, the radiator fans cool the engine when the car computer detects overheating.
But why does a car overheat when the AC is off? A faulty thermostat, radiator fan, or coolant can cause the car to overheat when the AC is off. Because when the AC is on, both fans help keep the engine at optimal temperatures. So, to fix the problem, you should replace the failing part.
Car overheating risks damage to the engine and its parts if not solved soon. Read on to learn more about why the car overheats when AC is off and some possible solutions.
Why Does a Car Overheat When AC is off?
The scene where the car overheats when the AC is off is less common but frustrating and time-consuming to diagnose. The car engine and interior will remain optimal when the air conditioning is on but start heating when it’s turned off.
Most cooling systems involve a radiator, a thermostat, and fans. These parts are responsible for keeping the engine and the car interior at an ideal temperature. If one or two parts of the cooling system malfunctions, it can cause it to overheat.
However, a vehicle overheating when the AC is off is not the same as the engine generally overheating. The table below shows reasons why your car might be experiencing this type of overheating.
| Causes | Solutions |
| A faulty thermostat | Replace the thermostat |
| Faulty Radiator Fan | Repair or replace the fan |
| Coolant Problems | Fix leakages and refill it |
| Faulty temperature sensor | Replace the temperature sensor |
In the following section covers the points in the table in depth
1. Faulty Thermostat
A thermostat controls the coolant by holding it when the engine is warming. When the engine reaches operating temperatures, it opens up and allows the coolant into the radiator.
If the thermostat is stuck or doesn’t open completely, it might be the reason for the overheating. When you turn on the AC, the fans might provide enough air to cool the engine. However, when the AC is turned off, the radiator fan is overwhelmed and unable to cool the engine.
Solution
Most times, you must replace the thermostat to fix the overheating problem. A thermostat costs between $20 and $100, and the installation cost is between $150 and $300.
2. Faulty Radiator Fan
Most vehicles have two fans to help keep them cool when running in high temperatures. These fans include the air conditioning fan and the radiator fan that run together or one at a time. The car also has a blower fan that provides air to the interior when AC is on.
If the radiator fans are off when the AC is off, the fan’s ECT switch might be faulty. The engine coolant temperature (ECT) sensor sends a signal to the car’s PCM to activate the fan. Moreover, the fan might fail due to a blown-out fuse or a broken wire.
Solution
Test the fan by using jumper cables from your battery directly to the connector. If the motor doesn’t spin, replace the fan with a new one. If it works, check for a blown fuse or a faulty relay and replace it.
3. Coolant Problems
The coolant runs through the hoses that connect the engine to the radiator. It helps cool the engine by running through its interiors before exiting and cooling down at the radiator. The coolant might have any of the following problems, causing it to remain warm and cause overheating.
- Low pressure on the coolant – Low pressure in the coolant minimizes liquid-to-metal contact, and the coolant cannot cool the engine.
- Air in the coolant – Due to leakage or age, the coolant might develop air bubbles that can trap heat. These bubbles are not entirely cooled at the radiator and can cause the engine to overheat.
- Low coolant level – Low coolant level cannot effectively cool the engine because it has low pressure.
Solution
To fix coolant problems, drain the old coolant and replace it with a fresh one. However, you must ensure that there are no leakages in the hoses.
4. Faulty Temperature Sensor
The temperature sensor is installed in a thermostat or beside it to measure the temperature of the coolant. If it malfunctions, it can send the wrong signal to the ECU and the cooling system, causing the engine to overheat.
Solution
One way of fixing the problems is by replacing the temperature sensor with a new one. If your kind of sensor is inside a thermostat, replace the thermostat too. Drivers with this problem have also reported fixing their problem by changing the coolant temperature sensor.
How Do You Troubleshoot Car Overheating When AC is Off?
Like most problems, you can troubleshoot the overheating issues using an OBD-2 scan tool.
- Most vehicles have a port where you can connect the scan tool and check for faults in the system.
- Also, confirm that all fans work when the AC is on and off. The fans should also be running when the engine starts overheating.
- Check the condition of the fans and if there are any bunt motor fuses and replace them.
- Also, check for leakages in the hoses and if the coolant has air bubbles.
However, it’s best to take your car to a mechanic for a complete diagnostic. Running the engine while this problem is still on risks damaging the engine. Also, keeping the AC on is fuel-consuming and overworks the engine.
How To Avoid Overheating Problems When AC is Off
Troubleshooting and repairing an overheating problem is time-consuming. Most people have changed almost every part of the cooling system to no avail. You can avoid the overheating problem by following the tips shared below.
1. Avoid keeping The AC on all the time
Other than affecting your health and fuel economy, running an air conditioner constantly overworks the engine. Thus, the engine and its parts, including sensors, can become faulty, causing the overheating problem.
2. Regularly service Your Car
Servicing the car helps keep it in good shape and identify a problem early. You can identify a failing fan on time and replace it before it burns the motor.
3. Avoid Idling the Vehicle for Too Long
When the vehicle is idling, there is low air circulation through the engine, unlike when moving. Idling encourages overheating, damaging the engine and other parts.
FAQs
In this section, we have gathered some frequently asked questions related to the vehicle overheating problem.
Diagnosing an overheating car can range between $100 and $500, which varies with the vehicle. However, diagnosing and troubleshooting can be done at home using a scan tool.
Yes, it’s ok, but don’t drive for long using the AC because it strains the engine. Since running the AC keeps the engine cool, you can drive the car to the repair shop.
The cost of repairing an overheating car is between $200 and $1500, depending on the faulty parts. High-end vehicles might cost more if their replacement parts are expensive.
Bottom Line
The problem of vehicle overheating when AC turns on is the most common compared to when AC is off. However, despite being less common, the problem can be time-consuming to diagnose and fix. Luckily, with the idea of the part that is causing the problems, repairing is less complicated.
The article covers some of the reasons why your vehicle might be experiencing this problem and the solutions. Also, you can avoid the vehicle overheating when AC is off by following the given tips.