Car Dies When I Turn On Heater AC: 6 Reasons Why This Might Be Happening

What should I do if my car dies when I turn on heater? In this article, we explain why this happens and what you should do about it.

You usually turn on the heater of the car during cold winter months. The heater core provides warm air inside the car cabin. But what should you do if your car dies when you turn on the heater? You can’t just sit inside without a heater in the freezing cold!

Thankfully, there are only a few reasons why it could be happening. For instance, the idle air control valve or throttle body may have become dirty or have carbon deposits on them, making the car die. Sometimes, the compressor might have a problem, affecting the engine performance and leading to a stalled car. 

Let’s explore all this in more detail in the article below.

Car Dies When I Turn On Heater

What is a Car Heater AC?

When you feel cold, you turn on the car’s heater. The hot air starts flowing through the AC vents, which keeps you comfortable during the journey. In short, the car AC helps increase air temperature inside the car cabin compared to the outside air. 

But no car has a furnace to keep you warm throughout the journey. The cold air outside has to go through multiple steps and finally convert into warm air.

A thermodynamic process goes on inside the car, which helps remove cold from the cabin, and helps you feel warm and comfy. The air filters even absorb dust and dirt and provide clean air to breathe, which is vital for your health.

Also read – What to do if air is blowing only through the defrost vents?

How Does it Work?

The car AC works exactly as that of the room air conditioner. But a car is relatively small compared to your room. So certain modifications are done inside the car to fit the air conditioner in the car space.

The car AC heavily depends on refrigerant and is either in a liquid or gaseous state. The refrigerants are nonflammable and nontoxic to human beings. In earlier days, people used R-12 or Freon as the refrigerant. But it has chlorine atoms, damaging the ozone layer and thus permitting ultraviolet rays to enter the Earth’s atmosphere. 

Now, R-134 a is used in Car ACs. The best thing about R-134a is that it does not have ozone layer-destroying properties like R-12. The car AC mainly has four components, i.e., compressor, condenser, throttle valve, and evaporator.

The refrigerant enters the compressor at low pressure and temperature. It is compressed to high pressure and temperature, and then the refrigerant moves to condenser tubes. The condenser acts as a heat exchanger. 

The refrigerant discards the cold air outside and converts it to gas. While the temperature and pressure do not change, the refrigerant changes its phase, i.e., from liquid to gas.

Now the refrigerant moves to the drier. The drier has two significant functions. It acts as a filter and removes all the impurities from the air. Secondly, it absorbs all the moisture from the air so that only dry air goes to the expansion valve and evaporator. 

The liquid refrigerant moves to the expansion valves, drastically reducing the pressure and temperature. Now the refrigerant will move to the evaporator tubes.

It absorbs the cold air from the car cabin, converts it into a liquid state, and finally moves to the compressor. You get hot air as the refrigerant in the evaporator tubes sucks the heated air from the cabin.

Why Does The Car Stall if You Turn A/C on?

Below are a few possible reasons why the car stalls when AC is turned on.

#1. Idle Control Valve Malfunction

Idle mode is when the engine is in running condition, but the car stands still. The idle RPM of the car is between 600 to 1000 rpm. The engine has sufficient power on this rpm so that the car stands smoothly but does not stall.

But when you turn on the AC, it starts drawing a lot of power. The engine may not produce sufficient power in an idle RPM. So, it needs to increase the RPM, so the car will stand without stalling or dying out. 

The idle control valve helps to reduce these RPMs. It controls the amount of air that will pass the throttle valve and further changes the idle speed or RPM as required. 

So, whenever you turn the car into idle mode, the idle control valve helps to keep it running. But this builds up carbon in the valve, which can eventually cause a malfunction. The controller may send the wrong information to ECM and cause the car to stall. To solve this, you need to clean the idle valve from time to time.

Car Dies When I Turn On Heater

#2. Faulty Electronic Controlled Throttle Body.

The electronically controlled throttle body can have carbon deposits with time, which may result in the car stalling or shutting down. You need to clean the electronically controlled throttle body every few months.

#3. Seized Compressor

A seized air compressor is another significant reason the car stalls or shuts down when you turn on the heater or AC. The main work of the compressor is to convert low-pressure and-temperature refrigerant into the high-pressure and high-temperature refrigerant, for which it consumes almost 6 to 10 horsepower. 

This power is enough to reduce the engine RPM. Sometimes the compressor can seize because of a jam in the bearings, putting more effort on the belt, which may cause the engine to shut down.

#4. Damaged Belt

The belt connects the compressor to the engine, which draws power from it. But when the belt wears down with time, it causes fluctuations in the engine speed and leads to the car getting stalled.

#5. Overfilling Of Refrigerant

The refrigerant should not be too high or too low. If it is too high, it puts pressure on the engine, affecting its performance.

#6. Electrical Issue

If a fuse has blown or the relay switch has been damaged or become corroded, this can be another reason why the car shuts down.

How Does AC Impact The Car’s Engine?

The engine supplies power to the HVAC system of the car. So, turning on the AC significantly affects the engine performance. Below are a few factors that AC impacts on the car’s engine.

#1. Compressor Speed

You may have noticed that whenever you turn on AC there, the compressor immediately starts working, increasing the car’s RPM. This puts a load on the engine. Whenever the compressor speed is high, the engine will become more loaded.

#2. Climate Control

If the difference between the outside air temperature and the inside temperature of the car is high, the compressor will have to work more, putting more load on the engine.

#3. Conditions Inside The Cabin

The conditions inside the cabin also affect the car AC. If more occupants are inside the car, the AC has to work lesser to warm, affecting the engine performance. Other factors inside the cabin, like clothing and the metabolic rate of occupants, affect the car AC and thus affect the engine performance.

What Can You Do To Solve It?

  • You need to clean the idle control valve and electronic throttle body from time to time so that carbon will not get deposited on them.
  • Check the compressor belt from time to time. If the belt is worn out, then replace the belt with a new one.
  • The relay switch and the fuse must be in good condition.

Car Dies When I Turn On Heater

Frequently Asked Questions 

#1. Why does my car shut off when I have my AC on and I am at a complete stop?

If you have turned on your AC and your vehicle is in an idle state, the car may completely shut off. There can be numerous reasons. For example, if an idle control valve does not work effectively, your car will shut off. Similarly, if the compressor belt gets worn out, you will face the same problem.

#2. Does using the heater in your car drain the battery

The car draws energy from the high-voltage battery if you are driving an electric vehicle. So, it drains out the battery charge as long as you turn on the heater. You may experience car stalling if the battery dies or loses charge.

#3. What are the symptoms of vapor lock?

Vapor lock mainly occurs when the ambient temperature is relatively high, or you are driving at a high altitude. Additionally, if the fuel lines are near the exhaust system, it creates a vapor lock issue. The common symptoms of vapor lock include

  • Car stalling
  • The engine becomes too hard to run.
  • Poor acceleration

#4. Can a dirty air filter cause a car to stall?

The air filter helps get clean the air in the engine. But if the air filter is clogged with dust and dirt, it will interfere with airflow and may cause the car to stall. You will face the following problems when your vehicle has a clogged air filter

  • Decrease in engine performance
  • Lack of acceleration
  • Strange noise comes from the engine
  • Mileage gets reduced
  • Illuminates check engine light

#5. What are the symptoms of a weak fuel pump?

The fuel pump provides gasoline from the tank to a vehicle’s engine. But if the fuel pump does not work properly, then it can affect the engine’s performance. The symptoms of a bad fuel pump are as follows

  • The engine will run poorly
  • The engine will get overheat
  • The engine cannot maintain its speed
  • Fuel efficiency is reduced 

Wrap Up 

The Car AC and heater are essential in providing comfort to occupants sitting inside the cabin. But sometimes the car stalls when the AC or heater is turned on because it exerts extra pressure on the engine.

We have discussed above various possible reasons for which this problem occurs. You need to check the idle control valve and throttle body from time to time. Similarly, you should also check that the compressor is running smoothly.

Thank you for reading this article.

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Sean Mendez

Hi, I am Sean, a self-confessed petrolhead. I live in Boise, Idaho with a busy family of four and our energetic Labrador retriever. Thank you for visiting my website. You can find my email on the contact page.

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