4 Symptoms of a Bad AC Pressure Switch [High or Low] (2023)

If you're like most car owners, you probably don't think about the AC pressure switch until there's a problem, and if you're unlucky, fixing it can be a real headache.

Today, we'll look at the symptoms of a bad AC pressure switch and help you find the spot. Plus, our guide reveals how to test a faulty AC switch and discusses the potential cost of replacement.

Some of these symptoms are easier to diagnose than others. Additionally, there are some AC system trouble codes that may point you in the right direction. Let's take a look at the most common signs.

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Symptoms of a Bad AC Pressure Switch

The most common symptom of a bad AC pressure switch is a faulty or intermittent air conditioning function. In most cases, you'll notice this during hot days when cool air isn't blowing through the vents.

To find out how to resolve the issue, let's take a look at a more detailed list of the most common signs of a faulty AC pressure switch:

1. Intermittent air conditioning

4 Symptoms of a Bad AC Pressure Switch [High or Low] (1)

This AC system symptom can appear in many ways. You may notice that the system boots and goes offline for a short period of time. Or it might only work occasionally, leaving you warm most of the time.

Anyway, when the air conditioner only offers intermittent use, it's a good sign that the AC pressure switch is bad. To get comfortable again, you will need to replace the switch.

RELATED:9 Reasons Why Your Car's Air Conditioner Doesn't Blow Cold Air

2. Air conditioning stops working

What's worse than intermittent air conditioning? And when does it stop working? If your air conditioner is not working, the coolant pressure switch sensor may be faulty.

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

3. Blows hot air

When you turn on the air conditioner, you expect to feel cool air coming out. However, when the AC pressure switch fails, hot air may be all you get.

However, this problem is also caused by low coolant levels, which need to be checked regularly.

4. Strange noises from the air conditioning system

If the compressor cycles off and on, you will notice some strange sounds from the engine and under the dash. It will sound like the clicking sound that occurs when the compressor turns on normally, except that the air will not work.

Listen for the various clicks under the car's dashboard and in the engine compartment, telling you that the switch has turned the compressor on and off.

RELATED:6 symptoms of a bad air conditioning compressor

AC Pressure Switch Location

4 Symptoms of a Bad AC Pressure Switch [High or Low] (2)

AC pressure switches are located on the AC tubes on either side of the AC compressor. You will find the low pressure AC switch on the low pressure side (smaller pipe) and the other on the high pressure side (large pipe).

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

Most AC pressure switches are located inside the engine compartment, but some manufacturers place them elsewhere. A look at the service manual will show you the proper location for your model.


4 Symptoms of a Bad AC Pressure Switch [High or Low] (3)

AC pressure switch function

The function of the AC pressure switch is to provide safety control over the AC system. It is responsible for monitoring the refrigerant pressure on the low and high pressure sides of the AC compressor. One monitors the high pressure side, while the other evaluates the low pressure side.

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

The high pressure switch controls any blockage in the system that could generate more pressure on the high side. If the pressure gets too high, an explosion can occur in the system. That's why the switch tells the system to turn off the air conditioning so there's no more pressure.

How to test an AC pressure switch?

To test an AC pressure switch, you can use amultimeter🇧🇷 Use the ohms setting on your multimeter and measure between the signal and ground pin. The ohm should be 0 when the switch is closed and no open circuit when it is open. However, check arepair manualto the correct values ​​for your car model.

Here are some more steps on how to test an AC pressure switch:

1.Turn on the Air Conditioning

Leave the engine running and turn the air conditioning on full blast. Make sure you have the windows open so the air doesn't circulate on its own.

The first sign that the A/C pressure switch is bad is when the system intermittently shuts off. This should not happen with open windows.

RELATED:5 symptoms of a bad air conditioning condenser

2.Look for trouble codes

With the OBDII port on your vehicle, you can use acode scannerto check for DTCs. You can also use code scanner to clear codes after fixing the issue.

If you don't have an engine code reader, consider stopping by your localauto parts store, where they could offer the service for free.

If you find a trouble code in the AC pressure switch circuit, you should measure the switch wires, and if they appear to be OK, you should replace the AC pressure switch. If the error code indicates that the pressure is too low, it could also be due to a low coolant level.

Many modern vehicles have an electronically controlled AC system and in this case you can view the values ​​coming from the pressure sensors with the scanner. Connect your OBD scanner, activate the AC system and check the values ​​coming from the AC pressure switches.

3.Test electrical connections

If your car does not have the ability to check the AC system with a scanner, then you will have to do it manually. The first thing to do is check a wiring diagram and repair manual for your specific car model.

Check if your AC pressure switch has two or three wires. If there are two wires, it's usually just a signal and ground wire. If there are three wires, you probably have a 5 volt, signal, and ground wire. However, you need to confirm this with a wiring diagram.

Measure between the signal and ground pin with a multimeter and check the ohms. You should see 0 ohms when the switch is closed and an open circuit when the switch is open. Normally, the AC pressure switch is closed when the pressure is correct and works correctly.

You can also measure 5 volts, ground, and an engine control module signal at the AC pressure switch connector. If there are any problems with the values, you should check the wiring. However, you need a wiring diagram for this.


4.Check AC pressures

If your AC pressure switch looks good, use the AC gauge set to check that the levels are adequate on both sides. You will connect the low pressure gauge to the low pressure fitting and vice versa.

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

If the low or high pressures are off, then the coolant may need to be replenished or there may be a larger problem with the system.


AC Pressure Switch Replacement Cost

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

When you replace the AC pressure switch, in most cases it is not necessary to drain and refill the cooling system, because there is a check valve inside the AC pipe that does not allow the refrigerant to leak even if you remove the AC pressure switch.

However, carefully remove the AC pressure switch to confirm that this is the case for your car model.

common questions

What does the AC pressure switch control?

AC pressure switches monitor the low and high pressure sides of the air conditioning system. If the pressure on either side gets too high or too low, it will shut off power to the AC compressor and turn off the air conditioning system.

How do you bypass an AC pressure switch?

It depends on what type of AC pressure switch your car uses, but if it's an old two-pin switch, you'll just have to run a wire between the pins instead of the switch to get around it. However, this is not recommended as it can cause damage to the system. Check a wiring diagram and repair manual first.

Are the AC pressure switches normally open or closed?

The AC pressure switch circuit is normally closed during operation, so if a wire is damaged or a circuit opens, it will shut down the AC system to prevent further damage. However, you should consult a repair manual to confirm this for your specific car model.

How do you bypass an AC pressure switch?

To bypass an AC pressure switch, if you have an older two-pin switch, simply remove the connector and connect a wire between the connector pins. However, only do this if you know what you're doing and check a wiring diagram as it could seriously damage things.

How often do AC pressure switches fail?

In older cars, it was more common for the AC pressure switches to fail. However, on modern car models they look quite reliable, even if they are more advanced than before. Generally, an AC pressure switch will fail once or twice in the life of a car.

Can you drive with a faulty AC pressure switch?

Yes, you can drive your car with a faulty AC pressure switch without any problems, but the AC system will not work. When the AC pressure switch is bad, it will shut off the power sent to the AC compressor, which then will not activate and cool the air conditioning system.

Conclusion - AC Pressure Switch

The AC pressure switch is an important part of your air conditioning unit. If it doesn't work properly, you could end up with an expensive repair bill, so it's important to get it fixed as soon as possible.

The main symptoms of a bad AC pressure switch include:

  • intermittent air conditioning
  • Air conditioning stops working
  • blow hot air
  • Strange noises from the air conditioning system

However, working with air conditioning systems can be difficult and even illegal in some countries due to the fact that releasing refrigerant into the air is very harmful to the environment and there are some dangers in handling refrigerant. Therefore, taking your car to a mechanic is recommended if you feel like you don't know what you're doing when fixing AC systems.

To know more:

  • How much does it cost to repair a car's air conditioning?
  • How much does an AC recharge cost? (Average per model)


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