Most car owners don’t think about their AC pressure switch until something goes wrong, and if you’re not lucky, that may be stressful.
We’re going to look at the signs of a bad AC pressure switch and help you find the location. In addition, our guide covers how to test a bad AC pressure switch and discusses potential replacement costs.
Some symptoms are easier to diagnose than others, and there are some AC system trouble codes that can help point you in the right direction. So, what are the signs of a bad AC pressure switch?
4 Symptoms of a Bad AC Pressure Switch (High or Low)
The most common symptom of a bad AC pressure switch is a bad or inconsistent air conditioning operation. Most of the time, you will notice this on hot days when there is not cold air coming out of your vents.
To see how we can remedy the problem, let’s turn to a more detailed list of the most common symptoms of a malfunctioning AC pressure switch:
#1. Intermittent Air Conditioning.
This symptom with the AC system may appear in many different ways. You could notice that the system will turn on and shut off a little while later. Or, it may just be working sometimes, meaning you are hot most of the time.
Regardless, when the air conditioning is only working intermittently, that is usually a good indicator the AC pressure switch is malfunctioning. You will need to have the switch replaced to be comfortable again.
#2. Air Conditioning Stops Working.
What’s worse than your air conditioning only sometimes working? When the AC doesn’t function at all. If your AC isn’t working, then the problem may be with the refrigerant pressure switch sensor.
However, there are a lot of parts to the air conditioning system, which means your problem could be something entirely different.
#3. Warm Air is Blowing.
When you turn on the air conditioning, you expect to feel cool air pouring out. But when the AC pressure switch is bad, you might only feel warm air.
Another cause of this problem can be low refrigerant, check refrigerant levels regularly.
#4. Strange Air Conditioning System Noises.
If the compressor is cycling, you will hear some odd noises both from the engine and under the dashboard – it will sound like the clicking that happens when the compressor would normally turn on, except it won’t blow air.
Listen for the clicking sounds both from underneath of the dashboard and from the engine compartment, indicating that the switch is cycling the compressor on and off.
Location of the AC Pressure Switch
The AC pressure switches can be found on the AC pipes on each side of the AC compressor with the low side AC switch on the low side (smaller pipe) and the high side switch on the high side (large pipe).
The low side switch is located before the AC compressor, and the high side switch is located after the compressor.
Most AC pressure switches are found under the hood, but some manufacturers do not place the switches under the hood. You can look in your service manual for the exact location for your model.
Function of AC Pressure Switch
The AC pressure switch functions for safety monitoring of the AC system. It is responsible for monitoring refrigerant pressure on the low and high-pressure sides of the AC compressor. One switch is for the high-pressure side and the other is for the low-pressure side.
The low-pressure switch ensures that the system never gets too low. If it does, it is usually due to a leak. If the refrigerant is being pumped out of the compressor at an incorrect pressure, the compressor can be significantly damaged, requiring repair.
The high pressure switch monitors any blockage in the system that would cause more pressure on the high pressure side. If the pressure gets too high it can cause a rupture in the system. This is what the switch is supposed to do; tell the system to cut power to the air conditioner, so no more pressure builds up.
How To Test An AC Pressure Switch?
To verify your A/C pressure switch, the easiest way is to use a multimeter. Simply set your multimeter to Ohm mode and measure between the signal and the ground pin.
You should get 0 ohm when the switch is closed, and no open circuit when it is open; however, you will want to reference a repair manual for your year, make, model and proper specs.
Here’s a few more detailed steps on how to test an A/C pressure switch:
1. Crank the Air Conditioning.
With the window wide open, leaving the engine running, turn the air conditioning on full blast.
The first warning sign of a bad A/C pressure switch is if the system shuts off intermittently. That should not happen with the window wide open.
2. Scan for Trouble Codes.
With the OBDII port on the vehicle, the easiest way to check for DTCs is to simply use a code scanner for the OBDII port. You can then use that same code scanner to erase the codes once you correct the problem.
If you do not have a engine code reader, consider stopping at the local auto parts store, they may perform that service for you for free.
If the trouble code points to the module that references the A/C pressure switch: then use a test meter and measure the wires to the A/C pressure switch. You can replace the switch if everything looks good on the wire side of things. If the error code states low pressure, it might suggest low refrigerant levels.
Many modern vehicles have electronically controlled A/C systems, and if that is your situation, you can see the values coming from the pressure sensors using the OBD scanner. Connect the OBD scanner, turn on the A/C system and verify the values coming from the A/C pressure switches.
3. Test Electrical Connections.
If your car cannot check the AC system with a scan tool, you will have to do it by hand. First, you will want to check a wiring diagram and repair manual for your vehicle.
Next, check to see if your AC pressure switch has two or three wires. If there are two wires, those will typically just be a signal and ground wire. If you have three, it will more than likely be a 5 volt wire, signal, and ground. However, it is best to confirm with a wiring diagram.
Using the multimeter, measure between the signal and ground pin and check Ohms. You should have 0 Ohms when the switch is closed and an open circuit when the switch is open. Typically, the AC pressure switch will be closed when the pressure is correct, and in turn, the AC system is working correctly.
You can also measure to see if you have 5 volts, ground, and a signal coming from the engine control module at the AC pressure switch connector. If the values are not correct, you could try to check the wires, but once again, a wiring diagram will confirm this.
4. Check AC Pressures.
If the AC pressure switch checks out OK, you can use your air conditioning gauge set to check for adequate levels on both sides. You will hook the low-pressure gauge on the low-pressure fitting and vice versa.
On the low-pressure side, you should see around 30 PSI when the outside temperature is around 90 degrees or less. On the high side, you should see a reading of about twice the ambient temperature, then you should add 50 PSI.
If the low or high pressures are off, either there wasn’t enough refrigerant or there is a larger problem with the system.
Cost to Replace an AC Pressure Switch
The cost to replace an AC pressure switch ranges from $50 to $300 on average; the circuitry can cost between $20 and $100, while labor can be anywhere from $30 to $200 depending on how hard it is to access the sensors.
In most scenarios, you do not have to drain and refill the coolant system, because a check valve in the AC pipe does not allow refrigerant to pour out until the AC pressure switch is removed.
You should, however, remove the AC pressure switch gently to check if it will still be in place for your car model.
What does the AC pressure switch do?
AC pressure switches monitor the high- and low-pressure sides of the AC system. If the pressure gets too high or low, the AC pressure switch will shut off the power to the AC compressor and turn off the air conditioning system.
How do you bypass an AC pressure switch?
It generally depends on what type of AC pressure switch your car uses, but, in most cases, if you had an older two-pin switch, you could just take a wire and jump across the two pins instead of the switch to bypass it.
Although, bypassing it is not a very good idea, as it could cause system damage. Check a wiring diagram and repair manual beforehand.
Are AC pressure switches normally open or normally closed?
The AC pressure switch circuit is normally closed when operating, so if a wire shorts out or there is an open circuit, it will take power away from the AC system. You might want to check a repair manual to be certain on your specific car model.
How do you jump an AC pressure switch?
You should only jump an AC pressure switch if you are aware of what you are doing, but if it is an old two-pin, you can just take off the connector and bridge a wire between the two pins of the connector.
Only do this after checking a wiring diagram first, as you can really damage someone’s system if you don’t know what you are doing.
How often do AC pressure switches go bad?
On older cars, the AC pressure switch was much more common to go bad. However, on modern car models, they seem to be much more reliable, even if they are more advanced compared to before. In general, a pressure switch would go bad once or twice in the entire lifetime of the vehicle.
Can you drive with a bad AC pressure switch?
Yes. You can drive your car with a bad AC pressure switch if you would like. The air conditioning system just won’t work. When the pressure switch goes bad, it will shut off the power to the compressor, then it won’t engage the air conditioning system.
The AC pressure switch is a very important part of your air conditioning unit. If it is not working correctly, you may end up with an expensive repair bill, so should fix your pressure switch promptly if you find a fault with it.
However, working with AC systems may prove difficult and illegal in some countries because there are pollution issues with releasing refrigerant and there are dangers with the refrigerant sometimes too.
Its probably best to take your car to a mechanic if you do not feel that you know what you are doing with AC repair work.