How To Bypass Evaporator Temperature Sensor [Is It Possible?]?

Are you having issues with the evaporator temperature sensor in your car, and do you want to know how you can bypass it? You’ve come to the right place, because we have researched this question and have the answer for you.

Yes, it is possible to bypass the evaporator sensor in your car. To bypass the sensor, look for the sensor and connect a jumper wire across its two connectors.

We'll talk more about the evaporator and how it works with the other parts of the air conditioning system of your car in the succeeding sections. Read on to learn whether it is a good idea to bypass the evaporator temperature sensor.

How Does A Car's AC System Work?

A car's AC system takes advantage of the changes in the state of the refrigerant. A refrigerant changes from one state to another very easily. The slightest shift in temperature can cause the refrigerant to change from liquid to gas or vice versa.

The AC Compressor

The workhorse of the AC system is the compressor. This is where the air conditioning cycle begins.

The compressor uses the rotary power of the engine to do what it needs to do. The compressor has a pulley that connects to the serpentine belt, and the serpentine belt draws power from the crankshaft.

When you turn on your engine, the crankshaft starts to turn. The crankshaft’s rotation also rotates the serpentine belt that rotates the compressor’s pulley.

However, your AC is not always on.

The compressor’s pulley will always spin with the spinning of the crankshaft. However, unless you turn on the AC, the compressor’s pulley will spin without affecting the compressor.

Mechanic checking the evporator of a car

There is an electromagnetic clutch that engages and disengages the compressor. Turning on the AC will activate the magnetic clutch and allow the compressor’s pulley to engage the compressor.

Once the compressor activates, the pistons inside it will start to compress the refrigerant inside that is in gas form and increase its pressure. The increase in pressure will also increase the temperature of the refrigerant.

The refrigerant enters the compressor with a pressure of 43.5 pounds per square inch. When it leaves the compressor, its pressure goes up to around 232 pounds per square inch, and its temperature becomes 120 to 140 degrees.

Brand new car evaporator, How To Bypass Evaporator Temperature Sensor [Is It Possible?]?

This super-hot gaseous refrigerant goes into the condenser.

The tube coming from the compressor is also the start of the high-pressure side of the AC system.

The Condenser

The condenser looks like a small version of the radiator. It has small tubes that snake around its surface. The tubes absorb heat from the refrigerant and spread it.

Thin fins connect the tubes to each other, making it easier to distribute heat from the refrigerant. When the air from outside blows through the fins, the heat transfers to the air and exits to the other side of the condenser.

The movement of air through the fins of the radiator drops the temperature of the refrigerant so much that it turns to liquid that bears the same high pressure. Thus, the refrigerant leaves the condenser as a liquid under high pressure.

The Dryer

The high-pressure liquid refrigerant travels from the condenser to the dryer. The dryer traps debris, contaminants, and moisture from the refrigerant.

It is also responsible for trapping any remaining refrigerant gas that did not turn into liquid.

The AC’s dryer looks like a metal canister that you’d find between the condenser and the expansion valve.

The dryer also serves as a reservoir for coolant and oil when your AC system is cooling at a lower capacity. The reservoir side of the dryer is where the gas form of the refrigerant stays.

Since the dryer is responsible for trapping contaminants, you should replace it whenever there is work done on your AC system.

High-Side Service Port

The high-side service port or the high-side charge port is a quick access fitting where mechanics access the high side of the auto AC system. It has a valve and a valve cover that manufacturers use to charge the AC system at the plant.

Expansion Valve

The expansion valve receives a completely liquid refrigerant.

It is responsible for converting a high-pressure refrigerant liquid into a low-pressure refrigerant liquid. The pressure drop rapidly cools the liquid refrigerant.

The expansion valve also serves as a regulator of the flow of refrigerant as it leaves the expansion valve.

Car mechanic holding an old car expansion valve

The tube exiting the expansion valve is the start of the low-pressure side of the AC system of your car.

The movement of the liquid refrigerant from the expansion valve causes it to spray the refrigerant into the evaporator.


The low-pressure refrigerant in liquid form exits to the evaporator. The evaporator also looks like a small version of the radiator.

The liquid refrigerant cools the fins of the evaporator. A blower fan pushes air through the evaporator, and its temperature drops. It will then enter the cabin as cold air and cool the cabin.

The warm air inside the cabin that the blower fan pushes through the evaporator transfers heat to the fins of the evaporator. This heat raises the temperature of the refrigerant. 

The rise in the temperature of the refrigerant is enough to turn the refrigerant back into a gas form.

Detailed photo of a car evaporator on a white background

Thus, refrigerant exits the evaporator as a gas. Once it leaves the evaporator, it passes the low-side service port.

The low-pressure gaseous refrigerant travels to the compressor, and the AC system’s cycle starts once more.

Evaporator Temperature Sensor

The evaporator temperature sensor is a thermistor that activates at low temperatures.

Thermistors are sensitive to changes in ambient temperature. They are a type of resistor whose resistance changes as the temperature changes.

The type of thermistor in an evaporator temperature sensor increases its resistance with the drop in temperature.

When the temperature becomes too low, the resistance becomes so high that electrical energy will stop passing through the circuit of the evaporator temperature sensor.

This circuit supplies electricity to the compressor’s electromagnetic clutch. Without electricity, the compressor’s clutch will not engage, and the refrigerant cycle will not start. As a result, your AC system will not produce cold air.

This gives the evaporator time to thaw.

The sensor prevents the AC system from overexerting itself while the evaporator is frozen. This protects the compressor and other components of the AC system from damage and premature wear.

Why is a frozen evaporator bad?

A frozen evaporator pushes the system to work harder. The blower will have a hard time pulling air from a frozen evaporator because the ice will block the airflow.

Ice in the AC system will also cause corrosion on the components of the system.

If the cabin air filter is dirty, the airflow to the evaporator might not be enough to transfer the heat from the cabin air to the evaporator, causing it to freeze. This is a sign that you need to replace the cabin air filter—an easy DIY repair.

Additionally, if your evaporator freezes, there is water buildup outside the AC system. This would mean that the condensate drain has a blockage that prevents water from escaping the system. The low temperature of the evaporator freezes the water.

The last reason why an evaporator would freeze is when the AC system is low on coolant.

Can You Bypass The Evaporator Temperature Sensor?


Bypassing the evaporator temperature sensor is easy. You just need to install a jumper cable to bridge the circuit that the evaporator temperature sensor is guarding.

The evaporator temperature sensor is like a switch that is on most of the time. But it turns off when the temperature gets too low.

If you insert a jumper cable to bridge the two ends of the temperature sensor, then you would effectively bypass the sensor—an easy modification.

However, you will need to determine the location of the two wires that go to your evaporator temperature sensor.

Brand new car eveporator in a box

The first step is to determine if your car’s AC system has an evaporator temperature sensor. This is a new component. Not all new cars have it.

Once you’re sure that you have the sensor in your car, determine its location. It needs to be close to the evaporator or on the evaporator itself so that it will be able to monitor its temperature.

After you find the sensor, get a jumper cable to connect the two wires that connect to the sensor.

Why Bypass The Evaporator Temperature Sensor?

The only reason to bypass the evaporator temperature sensor is when it fails. A bad sensor will prevent the compressor from activating because it will block the flow of electricity to the electromagnetic clutch.

If you need to do a long drive on a hot summer day, a bad sensor will be the last thing you want.

However, you need to remove the bypass after you replace the failing sensor.

Old and used car evaporator compared to a new one

Leaving the bypass on and not replacing the sensor can lead to bigger problems.

The evaporator temperature sensor helps protect your AC system by preventing the compressor from activating when there is something wrong with the system, like when it’s low on refrigerant.

Some of the problems manifest in the evaporator, which is why the temperature sensor monitors the evaporator’s temperature.


Bypassing the evaporator temperature sensor is simple. However, it can lead to costly problems down the road.

If you enjoyed reading this article, you might find the articles below helpful:

How Long Can A Car Battery Run An Air Conditioner?

Does Check Engine Light Come On For Air Conditioner?

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