4 Symptoms of a Bad AC Pressure Switch (High or Low)

How can you tell if your car has a bad AC pressure switch? Read on to learn the most common symptoms.

ac pressure switch

When the weather gets hot, you want to know that your car’s air conditioning will run the way it should. However, when there is a bad AC pressure switch, it can become difficult to cool off.

We look at the symptoms of a bad AC pressure switch and help you find the location. Plus, our guide reveals how to test a bad AC pressure switch and discusses the possible replacement cost. 

Some of these symptoms are easier to diagnose than others. Plus, there are a few AC system trouble codes that might lead you in the right direction. Let’s take a look at the most common signs of a bad AC pressure switch:

The most common symptom of a bad AC pressure switch is a faulty or intermittent air condition function. In most cases, you will notice this during hot days when there is not blowing any cold air through the vents.

To find out how to solve the problem, let’s take a look at a more detailed list of the most common symptoms of a bad AC pressure switch.

Bad AC Pressure Switch Symptoms

1. Intermittent Air Conditioning

ac blowing air

This AC system symptom can show up in numerous ways. You might notice that the system starts up and cuts out for a short time. Or, it might only work occasionally, leaving you hot most of the time. 

Either way, when the air conditioning only offers intermittent usage, it’s a good sign that the AC pressure switch is faulty. To become comfortable again, you will need to have the switch replaced.

RELATED: 9 Causes Why Your Car AC is Not Blowing Cold Air 

2. Air Conditioning Stops Working

What’s worse than the air conditioning working intermittently? How about when it stops working at all? If your AC doesn’t run, the refrigerant pressure switch sensor might be defective.

However, many components make up the air conditioning system, so your problem could be entirely different. 

3. Warm Air is Blowing

When you turn on the air conditioning, you expect to feel cold air pour out. However, when the AC pressure switch goes bad, warm air might be all you get. 

However, this problem is also caused by low refrigerant levels, which should be checked regularly. 

4. Strange Air Conditioning System Noises

If the compressor is clicking off and on, you are going to notice some strange sounds. It will sound like the clicking occurring when the compressor normally activates, except the air won’t work. 

Listen for the distinct clicking noises, telling you that the switch turns the compressor off and on. 

RELATED: 6 Symptoms of a Bad AC Compressor

AC Pressure Switch Location

ac pressure switch location

The AC pressure switches are located on either side of the AC unit. You will find one switch on the high side and another on the low side. 

The low-pressure side switch is found before the AC compressor, while the high-pressure switch comes after the compressor. 

Most AC pressure switches are found within the engine compartment, but some manufacturers put them elsewhere. A look in your service manual will show you the appropriate location for your model. 

AC Pressure Switch Function

ac high pressure switch

The AC pressure switch function is to provide a safety monitor over the system. It is responsible for monitoring refrigerant levels on both the low- and high-pressure sides of the AC unit. 

That’s why you have two separate AC pressure switches on your vehicle. One monitors the high-pressure side, while the other is evaluating the low-pressure aspects. 

The low-pressure switch ensures that the pressure never drops too low. This problem is caused when a leak occurs. When the AC compressor pumps out refrigerant without the right pressure, it can cause significant damage to the compressor, leading to higher repair costs. 

The high-pressure AC switch monitors any blockages in the system that would lead to more pressure. If the pressure builds up too high, there could be an explosion in the system. That’s why the switch tells the system to shut off power to the air conditioning, so no more pressure builds up.

As you can see, both of these switches operate as safety sensors, protecting not only the AC system but also you and your occupants from danger. 

How to Test an AC Pressure Switch

mechanics diagnose car

If you have some basic mechanical knowledge, you can follow these AC pressure switch diagnostic steps to figure out what’s going on.

1. Turn On Air Conditioning

Leave the engine running and turn on the air conditioning full blast. Make sure you have the windows open, so the air doesn’t cycle itself.

The first sign that the air conditioning pressure switch is bad is when the system shuts off intermittently. This shouldn’t happen with the windows wide open. 

2. Feel the Condenser Tubes

Pop the hood and look for the condenser. It is a grille-shaped or block component that connects to the compressor with tubes and hoses. It also contains a belt and pulley system.

Feel both tubes coming from the condenser, moving toward the firewall. They should be cold to touch because refrigerant should be flowing through them. 

If one of the tubes doesn’t feel cold, there is no refrigerant moving through the line. 

RELATED: 5 Symptoms of a Bad Car A/C Condenser

3. Check AC Pressures

Use your air conditioning gauge set to check for adequate levels on both sides. You will attach the low-pressure gauge to the low-pressure fitting and vice versa. 

On the low-pressure side, you should see readings near 30 PSI when the temperature outside is 90 degrees or less. The high-pressure side should be around twice the ambient temperature with 50 PSI added. 

If the low or high pressures are off, there is a larger problem with the system. 

4. Scan for Trouble Codes

With the OBDII port on your vehicle, you can use a code scanner to check for DTCs. You can also use the code scanner to erase codes once you repair the problem. 

If you don’t have an engine code reader, consider stopping at your local auto parts store, where they might offer the service for free.

5. Test Electrical Connections

Take the pressure sensor off and test the connection heading to the sensor from the electrical harness. Make sure your key is turned on to the accessories spot. 

When the electrical connection is working as it should, the multimeter will read between 4.0 and 5.0 volts. 

AC Pressure Switch Replacement Cost

The average AC pressure switch replacement cost is between $50 and $300. To buy the AC pressure switch, you will likely spend between $20 and $100, while labor can cost $30 to $200, depending on how difficult it is to reach the sensors. 

Written by:

Magnus is the owner and main author of MechanicBase. He has been working as a mechanic for over 10 years, and the majority of them specialized in advanced diagnostics and troubleshooting. He has also been a motorsport (drifting) driver for over 5 years.