How to test ac pressure switch (bad ac pressure switch symptoms)

Are you facing issues with your car AC? Is it having trouble cooling off? Then maybe there are problems with the AC pressure switch. To be sure of this problem, you will need to be aware of your car’s failing AC pressure switch symptoms.

Don’t know anything about it? No need to worry. Here, I will go through all the symptoms of a bad AC pressure switch. I will also take you through how you can test a switch and how you can bypass it.

So, without wasting any more time, let’s get right into it.  

Bad AC pressure switch symptoms

Usually, there are some common symptoms that you may notice when you have an AC pressure switch issue. If you come across any of these, then you should consider the possibility of a bad AC pressure switch.

Irregular air conditioning

What this means is that sometimes your AC will work just fine, and sometimes it will fail to work. One common scenario of this symptom is that the AC starts up, then immediately cuts out. And after a short while, it comes back again.

When this happens, you will feel the heat inside your car more often. So, if you are finding your car getting hot, then keep track of the air conditioning. This is a clear sign of issues with the AC pressure switch.

AC completely stops working

Unlike the previous one, here, your AC may completely stop working. Well, when it works, sometimes it’s hard to determine the problem if you are not aware. But in this case, the problem is pretty evident as you will have no air conditioning in your car.

Now, something to consider here is that this problem can occur for various reasons. So, when you see this sign, it doesn’t always mean that the AC pressure switch has issues. Several other components are responsible for running your AC.

For determining the exact cause, you can run a test on the switch. I will be discussing that later on in the article.

AC starts blowing warm air

Naturally, an AC should put out cold air. But if your AC is blowing out warm air, then there is undoubtedly a problem with your ac. However, there are two possible reasons for this symptom.

It can be due to a bad AC pressure switch, and it can also cause by a lack of refrigerant in your ac. In this case, it’s better to check the refrigerant levels first because it’s much easier than testing your AC pressure switch.

Noises from your ac

Whenever your compressor activates, you hear a clicking noise. While that is normal, the continuous clicking noise isn’t a regular thing at all. When your AC pressure switch goes bad, you will hear the same noise from your compressor going on and off constantly.

This is an indication that the switch is turning the compressor on and off, which shouldn’t happen like that. It should either turn on or off at a time.

If you see these symptoms in your car, you should run the test on your AC pressure switch. These are symptoms of problems that are usually caused by a bad AC pressure switch.

Related: How to Purge the Air from the Heater Core

How to test AC pressure switch

Before you go ahead with this, let me tell you that you can do this test yourself with some basic mechanical knowledge. It doesn’t involve any complicated work, so you don’t need to be afraid. Just follow the steps below, and you are good to go. Let’s get going then.

  1. First of all, you have to turn your AC on and take it to its most absolute limit. Then, you have to open all the doors and windows of your car. It’s essential to do that because that way air won’t cycle inside. This stops the problem of irregular air conditioning.
  2. Next up is to check the condenser tubes. So, pop the hood of your car and then look for the condenser. It’s like a block connected to the compressor using tubes. You will also notice a belt and pulley system there.

Now, you have to check on the tubes and see if they are cold or not. If they are not cold, this means that refrigerant isn’t passing through them.

  1. Another test you can do is check the AC pressure. You can use a gauge for that. It’s pretty simple; you just attach the low end of the gauge to the low-pressure fit and do the same for the high end.

Typically, in a 90-degree environment, you should have 30 PSI on the lower end. For the higher end, it should be double the ambient temperature and an additional 50 PSI. If the pressure doesn’t seem legit to you, there is undoubtedly a problem with your AC pressure switch.

  1. If you have a code scanner and your car has an OBD II port, you can scan for any DTCs. If you don’t have a scanner, you can always go to servicing shops to provide this facility for free. Doing this will surely let you know if there is a problem going on with your AC pressure switch or not.
  2. Now, for the last test, you will need a multimeter. What you will be doing here is, have to test the electrical connections of your ac. To do that, you have to remove the pressure sensor and test the electrical connection that heads to the sensor. Keep in mind that the key is turned on toward the accessories spot while you are doing all this.

In the multimeter, you should get a reading of 4 to 5 volts. This reading means the connections are working fine.

So, these are the different tests you can run on your car to check up on the AC pressure switch. As you can see, they aren’t too complicated. Once you run them, you can quickly determine whether your AC pressure has gone bad or not.

Related: AC pressure too high in the car

How to bypass the AC pressure switch

Here’s the thing, if your AC pressure switch isn’t working but your system is all okay, then you can bypass the switch to make it work for a while. But make sure to do this temporarily because it’s not a permanent solution. Just do this until you get your AC pressure switch repaired or replaced.

Let’s check out how you can bypass AC pressure switch –

  1. Firstly, you will need two resistors of 1000-ohm. The color code for such resistors is brown, black, red, and gold. You have to join the one brown end of the resistor to the other gold end of the resistor.
  2. Now, connect the other two ends of each resistor on each side of the 3-pin sensor. As for the middle pin of the sensor, you have to use the resistor parts that you joined earlier.
  3. Once you do all this, your AC pressure switch should come live.

Something you have to keep in mind is that this is a method for a 3-pin sensor. For cars with a different sensor, you may need to consult a professional before doing anything. Or you can simply contact your dealer for solutions.

Bypassing the AC pressure switch tells you if there is a problem with it or not. This is an excellent method for those who don’t have a scanner to scan their cars for codes.


Here are some common questions people often ask about AC pressure switch –

  • Can I bypass my AC pressure switch?

Usually, when the pressure switch goes bad, it will stop cycling the compressor. But if you see your system working, then you can try out bypassing it. You can do that for a while until you replace the switch.

  • Can I test the AC pressure switch myself?

Yes, testing an AC pressure switch isn’t that difficult. You can do it yourself if you have some basic mechanical knowledge. Moreover, if you have an OBD code scanner, then the job becomes much more accessible.


To sum up, knowing the bad AC pressure switch symptoms is crucial to fix the problem. As you have already seen, there are several reasons for AC failure. So, when you can determine the cause of AC pressure switch failure, you can quickly fix it without going through too much trouble. And it’s the easiest one to solve as well.

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