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

If your AC pressure switch is not working, it can cause your whole AC system to malfunction. Here's how to tell if your AC pressure switch is bad

Symptoms Of A Bad Ac Pressure Switch

If you’re like most car owners, you probably don’t think about your AC pressure switch until there’s a problem, and if you’re unlucky that problem can be a real headache to fix.

Today we are going to 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 first.

What Are The Symptoms Of A Bad AC Pressure Switch?

The most common symptom of a bad AC pressure switch is a non-functioning air conditioning system in your car. You may notice that only warm air is blowing from the vents. In some cases, you may also hear strange noises coming from behind the dashboard.

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.

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 from the engine and under your dashboard. It will sound like the clicking occurring when the compressor normally activates, except the air won’t work. 

Listen for the distinct clicking noises from both under your car’s dashboard and in the engine compartment, telling you that the switch turns the compressor off and on. 

RELATED: 6 Symptoms of a Bad AC Compressor

Where Is The AC Pressure Switch Located?

Ac Pressure Switch Location

The AC pressure switches are located on the AC pipes on both sides 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 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. 

RELATED: Does AC Stop Leak Sealer Work? (& Is it Bad?)

Ac High Pressure Switch

What Does An AC Pressure Switch Do?

The function of the AC pressure switch is to provide safety monitoring over the AC system. It is responsible for monitoring the refrigerant pressure on both 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 out refrigerant without the correct pressure, it can cause significant damage to the compressor, leading to higher repair costs.

The high pressure switch monitors any blockages in the system that would lead to more pressure on the high pressure side. If the pressure builds up too high, an explosion can occur in the system. That’s why the switch tells the system to shut off power to the air conditioner, so no more pressure builds up.

How to Test an AC Pressure Switch?

To test an AC pressure switch you can use a multimeter. Use the Ohm setting on your multimeter and measure between the signal and the ground pin. The ohm should be 0 when the switch is closed, and no open circuit when it’s open. However, check a repair manual for the correct values for you car model.

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

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. 

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

2. 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.

If you find a trouble code on the AC pressure switch circuit, you need to measure the wires to the switch and if they seem good, you need to replace the AC pressure switch. If the error code says the pressure is too low, it could also be due to a low refrigerant level.

Many modern vehicles have an electronically controlled AC system, and in this case you can see 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 don’t have the ability to check the AC system with a scanner, you need to do it manually. The first thing you want to do is check a wiring diagram and repair manual for your particular car model.

Check if your AC pressure switch has two or three wires. If there are two wires, these are normally just a signal and a ground wire. If there are three wires, it probably has a 5 volt wire, signal and ground. However, you must confirm this with a wiring diagram.

Measure between the signal and ground pin with a multimeter and check 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 working properly.

You can also measure if there is 5 volts, ground, and a signal coming from the engine control module at the AC pressure switch connector. If there is something wrong with the values, you need to check the wiring. However, you need a wiring diagram for this.

RELATED: AC Low Side Pressure Too High – Common Causes & Repair Costs

4. Check AC Pressures

If your AC pressure switch seems to be fine, 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, you may need to refill the refrigerant, or there may be a larger problem with the system. 

RELATED: 5 Signs Your Car’s AC is Low on Freon (& What to do)

How Much Does An 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. 

When replacing the AC pressure switch, in most cases you do not need to drain and refill the coolant system, because there is a check valve inside the AC pipe that does not allow the refrigerant to pour out even if you remove the AC pressure switch.

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

What does the AC pressure switch control?

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

How do you bypass an AC pressure switch?

It depends on what type of AC push 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 bypass it. However, this is not recommended as it may lead to damage to the system. Check a wiring diagram and repair manual before.

Are AC pressure switches normally open or closed?

The AC pressure switch’s circuit is normally closed when operating, so if a wire gets damaged or an open circuit, it will switch off the AC system to prevent further damage. However, you need to check a repair manual to confirm this for your particular car model.

How do you jump an AC pressure switch?

To jump an AC pressure switch, if you have an old two-pin switch, simply remove the connector and bridge a wire between the pins of the connector. However, only do this if you know what you are doing and check a wiring diagram because you can damage things badly.

How often do AC pressure switches go bad?

On older cars, it was more common for AC pressure switches to go bad. However, on modern car models, they seem to be quite reliable, even if they are more advanced than they were before. Generally, an AC pressure switch will go bad once or twice in a car’s lifetime.

Can you drive with a bad AC pressure switch?

Yes, you can drive your car with a bad AC pressure switch with no problem, but the AC system won’t work. When the AC pressure switch is bad, it will switch off the power sent to the AC compressor, which will then not engage and cool the air conditioning system.

Conclusion

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 repaired as soon as possible.

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 bad for the environment and there are some dangers to handling the refrigerant. Therefore, it is recommended to take your car to a mechanic if you do not feel that you know what you are doing when repairing AC systems.

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