Top 5 Causes of the “ENGINE HOT AC TURNED OFF” Light

Our editors pick the products & services we write about. When you buy through our links, we may get a commission. Learn more.

Are you wondering why the engine hot AC off light keeps coming up on your instrument cluster? Are you curious about what the underlying issue might be and how to fix it?

This article highlights the problems that might cause the “ENGINE HOT AC OFF” or “ENGINE HOT AC TURNED OFF” light to flash on your instrument cluster. 

Towards the end, you will gain insight into diagnosing and fixing the fault, causing you much turmoil. Your driving experience will never be the same. 

Let’s dive into it!

What Does “ENGINE HOT AC OFF” Light Really Mean?

The PCM flashes the “ENGINE HOT AC OFF” light to indicate that the engine is overheating and that you have a dysfunctional cooling fan. At times, the two situations could be the primary source of the signal. Nevertheless, the PCM may flash the same light to indicate either of the scenarios has occurred.  

engine hot ac turned off
Malfunctioning thermostat, low level of coolant, blown head gasket, bad AC compressor, radiator cooling fan are the top causes of the light.

How Long Can I Drive With The “ENGINE HOT AC TURNED OFF” light?

There’s no specific number of miles you would drive your vehicle before damaging something that would cost you an expensive repair. You could drive for just 10 miles and end up having a whole engine overhaul, whereas someone else may drive for 20 miles, with zero implications on the engine. 

Whenever you notice the light come up on the instrument cluster, pull over your vehicle and check if the engine is overheating. In this case, it is pointless to drive as it may lead to an accident or possibly engine damage. Try figuring out the problem yourself or contact a mechanic if you’re not the DIY kind of person. 

Nevertheless, if the AC resumes normalcy and the coolant temperature drops, only then might it be safe to continue driving. 

Causes and How to Fix It

Malfunctioning thermostat, low level of coolant, blown head gasket, bad AC compressor, radiator cooling fan are the top causes of the light.

Now let’s find out the details of the problem and how to fix it.

1. Malfunctioning Thermostat (or Temperature Sensor)

A defective thermostat opens up too early, tripping a code to the PCM. Since the system no longer trusts the thermostat’s accuracy, it responds by switching the fans to high mode and turning off the AC, reducing the cooling load on the engine. The engine hot AC off light registers this change. 

In case you try switching the air conditioner on, it will flash thrice and fail to start. This condition is followed by the check engine light coming up on the instrument cluster. 

Additionally, you will notice that the coolant gauge reading would drop below 160, and nothing will register from there henceforth. 

A dysfunctional thermostat will quickly be identified by leaking coolant around it due to random temperature changes. Additionally, the temperature gauge will show high-temperature reading while the engine might overheat. 

Conversely, a problematic sensor would turn on the engine hot AC off light whether the engine is overheating or not. Other symptoms may include irregular temperature readings, poor fuel economy, and the exhaust emitting black smoke. 

A much easier way to identify the problem is using an OBD2 scan tool. The scanner will show a code P0128. The code denotes that the engine’s coolant isn’t warming up at the regular rate. Therefore, indicating that the engine is not operating at its optimal temperature. 

Here is how to go about replacing the thermostat:

  • Locate the thermostat under the vehicle’s hood and place a bucket beneath your working area.
  • Remove the clamp reinforcing the hose and pull it out. 
  • Disconnect the 10mm bolts securing the thermostat. 
  • Replace the thermostat with a new one and reinforce it with the bolts. 
  • Change the hose and its clamp.
  • Replace the spilled fluid from the hose. 

Why is the Light Still On After Replacing the Thermostat?

The light should go off on its own after replacing the thermostat. Nevertheless, if this fails, you will need to disconnect the negative battery terminal and reconnect it to reset the PCM. 

In case the problem persists, then it’s time to replace the temperature sensor. 

Below is how to do it: 

  • On purchasing a new sensor, release the system cooling pressure to your vehicle.
  • Locate the coolant temperature sensor and disconnect its electrical connector. Usually, it is next to the first spark plug. Therefore, it is prone to heat damage resulting in the wires to the plug being highly resistive to current flow. 
  • Replace the sensor with a new one. 
  • Ensure you reinforce all the parts you had let lose to access the sensor. 
4 signs of a bad or failing thermostat and how to check and test

2. Low level of coolant

If you’re running on low coolant levels, you’ll probably have zero or minimal control over the car’s heating system. You notice surging temperatures in the vehicle with alarming temperature recording on the instrument cluster. Next, you’ll have an extremely hot bonnet, and you’re likely to notice billowing steam. 

Low refrigerant level means that the radiator will run on insufficient coolant to keep the engine’s temperatures in the bay. This information is relayed to the PCM, which alerts you by switching the engine hot AC off. 

First, you should confirm from the car’s manual the most appropriate coolant for your vehicle. The oil should be added to the reservoir and not the radiator. Add the coolant to the recommended level. 

Keep your hands and clothes away from the fan as it may rotate even though the engine might be off. Ensure to fill the coolant to the cold engine line in the reservoir if the engine is cold. Both undiluted and diluted coolant may be used. 

Low Coolant Fluid Signs And Symptoms For A Car

3. Blown Head Gasket

The engine’s head gasket is responsible for sealing between the cylinder head and the engine block. It prevents hot gases and engine coolant from leaking. 

Having to disassemble the engine to see the head gasket makes it hard to diagnose its associated problem. In most cases, you will require a mechanic to rule that the engine overheated due to a defective head gasket. 

Performing a visual aid may not reveal much on how damaged the head gasket is. Therefore, you’ll need to check on other secondary issues. 

You should lookout for the following if you speculate that you have a blown head gasket:

  • Leakage of coolant, especially underneath the exhaust manifold. 
  • White milk-like discharge on the engine block. 
  • Low cooling system integrity.
  • Visible bubbles on the overflow tank or the radiator. 
  • Defective spark plugs.
  • White exhaust smoke. 

During the replacement of a blown head gasket, precaution should be taken with much seriousness as it could lead to damaging the engine or causing skin burns. 

HOW TO CHECK FOR A BLOWN HEAD GASKET

4. Bad AC Compressor

A defective AC compressor will be unable to circulate refrigerant in the AC system. This causes warm air to flow out through the AC vents. Check whether the vehicle’s interior has higher than average temperatures or you’re receiving hot air flows within the car. 

Although the AC might be on, a failing AC compressor may cause the engine to heat up due to the increased load. The compressor might be adding rotational engine load, and if it is continuously wearing out, it might become harder to turn, making the engine overheat. The best solution is to have a mechanic have a look at the problem and fix it. 

Symptoms OF A BAD A/C Compressor

5. Failing Radiator Cooling Fan

A faulty radiator fan produces a whirring or clicking sound. This noise results from bent compressor blades touching other components or a bearing that is out of place. 

A stalled or low-speed running radiator fan could cause the engine to overheat. Fans are designed to run by electric motors. Mechanical issues with the motor could lead to a complete stop or a low-speed turning fan. 

This means that the fan cannot provide the required cooling airflow to maintain the engine’s temperatures. The best way to handle the situation is to stop driving and let the engine cool on its own. After that, you could drive to the nearby repair shop or have a mechanic come to you and check the malfunctioning radiator motor issue. 

Engine Hot AC Turned Off Solved Suburban Tahoe Silverado

Can I Fix It Myself?

Yes. You can fix it yourself if you’re experienced enough.

While most problems are easy to fix on your own, others require some prior mechanic knowledge to perform the repairs effectively and quickly without any repercussions. Issues related to defective thermostats and temperature sensors are easy to fix while using little DIY techniques. 

However, a blown head gasket, dysfunctional AC compressor, and a defective radiator motor may require specialized skills. Have your mechanic repair them to avoid overly tedious work that could adversely affect your vehicle or yourself, especially if you’re only beginning to explore the car’s anatomy. 

How Much Does It Cost to Fix The Issue?

Resetting the lights after the fix won’t cost you a dime. Nevertheless, you cannot get rid of the light if at all there is a system problem. Some issues could be overly expensive to fix, while others may be a bit cheaper. 

For example, fixing a blown head gasket would cost you about $1,400 to $1,600. Temperature sensors may be worth $65 to $90, whereas radiator motors could cost you anywhere from $100 to $1,000 to fix. When all the fixes are made, only then will the engine hot AC off light be eliminated. 

Tips to Avoid the Light in The Future

The best practice to avoid this problem is always to ensure that your vehicle runs on sufficient oil. Service your car regularly, and don’t push your vehicle beyond the specified limits. 

Conclusion

Defective thermostats, temperature sensors, problematic radiator fans, low coolant level, and a damaged AC compressor are the primary reasons for the engine hot AC off light coming on your instrument cluster. Replacing them may require professional intervention, but some fixes could be done by yourself. 

Leave a Comment

Your email address will not be published. Required fields are marked *