How Does The AC Work in an Electric Car

Electric cars are growing in numbers all over the world. Word around is that they are cheaper to run and maintain. One of the few systems carried over from gas-powered cars is the AC. Many have been wondering, how does the AC work in an electric car?

Just like a traditional vehicle, the air conditioning system in an EV is designed to provide both heating and cooling. Instead of an engine, a battery pack acts as the powerhouse. Here’s how electric car air conditioning works.

How does the AC work in an electric car?

Cooling

An ordinary gas-powered car comes with an AC compressor that is powered by the engine. Its job is to pressurize the refrigerant (Freon) and pump it to the condenser.

The condenser turns the refrigerant from a gas to a liquid. This process allows it to flow to the evaporator where it turns into a gas again. The changes in state help to lower the temperature of the refrigerant.

A heater fan then blows warm air from outside through the evaporator for cooling. The cool air then enters the cabin.

The AC compressor is the power unit of the system. It is driven by an accessory belt that is connected to the engine.

In an electric car, an AC compressor is powered by a battery pack rather than an engine. Tesla uses a compressor similar to the one found in a domestic fridge. It works off 400V.

The compressor sits at the front of the car while the battery pack is located in the rear. Tesla uses the term Energy Storage System (ESS) to refer to its battery.

Similar to an internal combustion engine vehicle, the compressor in an EV pumps the refrigerant to a chilling unit where it cools the air going into the cabin.

Heating

An internal combustion engine generates a lot of heat during normal operation. It has passageways inside that allow coolant from the radiator to flow through. The coolant provides cooling and prevents overheating.

A thermostat monitors the temperature of the engine and regulates how much coolant is flowing inside. The water pump pressurizes the coolant for it to flow.

Once the coolant gets hot after absorbing heat from the engine, it flows to the heater core where it transfers that heat to the car.

When you turn on your heater, a blower motor spins to force air through the core. The air gets heated and flows into the cabin through the vents.

An electric car has none of these parts. So how does the air conditioning work? A Tesla Model 3 and other Teslas come with an electric heater in place of a heater core.

To prevent the heater from draining too much energy from the car’s battery, engineers went for a positive temperature coefficient (PTC) heater that comes with a resistor.

The resistor regulates and limits the flow of electric current when there’s an increase in heat. This in turn helps to control the amount of power the heater draws from the battery pack. It also ensures that the car doesn’t get too hot inside.  

Related: How to turn on the heat in your car

Heat Pump in Electric Vehicles

The Tesla Model Y and other EVs such as the Nissan Leaf use something called a heat pump to heat and cool the cabin. It’s more efficient and comes with a reversed order of operation.

For starters, it features a compressor, a condenser, an expansion valve, and an evaporator. The compressor is powered by the car’s battery. The refrigerant first enters into the compressor for compression at low temperature and pressure.

It gets compressed then travels at high pressure and temperature into the condenser where it cools down slightly but remains warm. This changes it to a liquid.

A blower motor blows air through the condenser for heating. The air draws the heat from the hot refrigerant and warms the cabin.

The high-temperature and high-pressure liquid then leaves the condenser and goes into the evaporator. It passes through an expansion valve that controls how much of it is flowing.

This helps to slow down the rate at which the liquid is getting into the evaporator, hence, reducing its temperature and pressure.

Outside air blows through the evaporator, heating and boiling the liquid up. The outside air is warmer than the evaporator and refrigerants typically boil at a very low temperature.

As the liquid boils, it absorbs a bunch of energy and changes into a gas. The gas finds its way into the compressor and the cycle continues. That’s how the AC gets to work in such an electric car.

Heat Pump Vs Electric Heater in EVs

At the time of writing this article, the heat pump is available in the Tesla Model Y but not in other Teslas.

It replaces the electric heater and resistor method used in other EVs because the latter affects the range of an electric vehicle.

It sucks power from the battery, reducing the amount left for your trip. Your electric car will not be able to hold as much charge when the AC is running.

A heat pump is 300 to 400 percent more efficient than an electric heater. It has a coefficient of performance of 3 or 4 compared to a coefficient of 1.

This is thanks to the pump’s ability to take the energy from outside the vehicle and stick it inside the car.

Energy flows in at two places (outside air as it passes through the evaporator and the battery which powers the compressor). The energy only leaves only at one place (condenser).

A resistive electric heater takes energy from the battery and moves it to inside the car, making it less efficient. A heat pump uses energy that already exists from the outside air.

However, it’s good to note that the colder it is outside, the less effective a heat pump will be. There will be less energy the pump can pull in.

At a certain temperature, the coefficient of performance will be the same as that of the resistive heater. This is due to the small difference in temperature between the evaporator and the outside air.

But this is less likely to happen since most places, other than Antarctica of course, have ideal driving conditions.

Radiators in Electric Cars

It’s good to note that electric cars have radiators. So why not use them to heat the car?

The first reason is that EVs are very efficient overall. This means that they generate less heat and will take forever to heat the coolant.

The second reason is that electric cars tend to have lower peak temperatures with their coolant.

The difference between the cabin’s temperature and the coolant temperature is small, thus providing very little benefit in heating the cabin. The AC would, therefore, not work as it should in an electric car.

Final Thoughts

I hope this article has helped you figure out how the AC works in an electric car. The controls are pretty much the same as those you’d find in a gas-powered engine. The only difference is the mechanism used to provide the heating or cooling and the designs of the vents.

Below are some additional resources that you can check out regarding air conditioning systems in vehicles.

How does defrost work in a car?

Why does my AC and heat only work on high?

How to replace the evaporator temperature sensor