Symptoms of a Bad or Failing AC Pressure Switch

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We all love the AC, right? When you’re rolling down the freeway in the middle of summer, how nice is it to flick a switch and be rewarded with a cooling gust of conditioned air.

It’s heaven on four wheels, lets not lie to each other. But what happens when you push the switch and get nothing back? The first thing to do is maybe panic, the second thing to do is start sweating like a pig in Texas.

The third thing is to get it sorted, and that is what we are going to help you to do in this article. If your AC is not working properly there is a good chance the error lies with the AC Pressure Switch. If you can spot the symptoms of this, you can tackle the problem.

But the first question is… just what the heck is an AC Pressure Switch?

What the Heck is an AC Pressure Switch?

Actually, you know what, if you want to know what a AC Pressure Switch is, then you kind of need to know how the AC actually works.

Ok… How Does the AC System Work?

It’s not a giant ice cube with a fan blowing over it, which is what one of our old College pals honestly believed.

(He’s a doctor now, so let that thought haunt your nightmares).

The Air Conditioning system in a car is actually a pretty complex system – it is in fact one of the most complex systems on a modern car. Yeah that’s right, the thing that stops you getting your back stuck to your seat is more complex than the vehicle exhaust system.

Anyway, it works on a dual system, where one side has refrigerant (or coolant) fluid at low pressure and the other has it at high pressure. On the low-pressure side it is a gas until it passes through a compressor. It is then liquefied and flows through the AC system into a component called a receiver or sometimes a drier. Here it cools the air blown through the system which emerges into the car as a cool blast of Arctic chill.

The refrigerant then exits the system under high pressure where it can be cycled back through the low pressure side to become a gas again before starting it’s magical cooling journey all over again.

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So We Ask Again: What the Heck is an AC Pressure Switch?

Clear as mud, huh?

All you need to know is the AC is split into two halves, one is a low pressure half and the other is high pressure – and that both sides are equipped with a AC Pressure Switch.

So what does this switch do? Well it is actually a very important safety device that is built into the AC system. Its main job is monitor the pressure of the refrigerant on both the low and high-pressure sides of the system.

This is actually very important because if the pressure is too low or too high, it can cause serious damage to the AC system.

Pressure: Too Low

If the pressure is tool low, then the risk is that the compressor can burn out. It will then be unable to compress the refrigerant from liquid to fluid, which will see your AC unit grind to a halt.

Bad news.

Pressure: Too High

If the pressure is too high, it could burst the compressor causing a leak of refrigerant fluid. If there is no fluid in the system, then it’s going to grind to a halt again.

Also bad news.

So really, you can look at the AC Pressure Switch as working in the same way as a fuse in an electrical circuit. It is a cheap component that is designed to monitor the operation of the far more complex (and far, far more expensive) system that it is plugged into.

So when they sense a problem they can overload and stop the system working to actually protect the system from damage. They can also simply be damaged themselves since they are pretty fragile.

Luckily if are damaged, are failing or have even failed completely there are a few easy to read symptoms to keep any eye out for. Amongst the most obvious ones are:

The AC Won’t Turn On

As we pointed out above, one of the main purposes of the AC pressure switch is to protect the compressor from damage from pressure in the refrigerant that is too high or is too low.

Sometimes the pressure switches will detect that the pressure is incorrect. When this happens, they can override the AC control system and stop the compressor from activating. When this happens, the result will be that every time you try to turn the system on in the vehicle cabin, there will be no cool air for you.

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The trouble is of course that often the AC Pressure Switches themselves will be damaged or failing or have already failed. In this instance, the AC system won’t receive their pressure readings from the pressure switches. Again, if this happens the AC system won’t allow the compressor to be activated.

No compressor means no AC.

AC Activates And Does… Nothing

Sometimes if the pressure switch is simply failing rather than full out failed, it can still allow the AC system to activate. However remember the important role in managing the pressure of the refrigerant as it works through the AC System that the AC Pressure Switches play.

This means that if one or, even worse, both switches are failing then the AC system will be receiving incorrect pressure readings from either the high or low side of the system. That means that the AC System won’t be working at its optimal rate.

What does that mean for you in the car? Well for one thing you will know your car better than us.  One of the things that you will know, especially if you live in a hot area, is the amount of time your AC system typically takes to cool a hot car. If you are noticing that this time is getting longer and longer then it could be the fault of a failing AC Pressure Switch stopping the system working properly.

You could also see this symptom manifesting as an AC system that just feels really weak. For example if you have started cracking the AC to Max and are still just getting a little trickle of cool air, that is definitely pointing to a failing AC Pressure Switch as the cause.

AC System is Turning Off/On Repeatedly

The next symptom is also somewhat connected to the one we discussed above. That is because this one can also make its self known as a symptom of a failing AC Pressure Switch.

This is because sometimes when a Pressure Switch is failing, instead of making the AC operate underpowered, it can make it do some other weird stuff instead. One of the big examples of this weird behavior is making the AC switch on and off over and over, often in very quick succession.

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Again this is a symptom that should be easy to pick up if you are used to the way that your AC system operates. This is because most AC systems will automatically cut off for periods of time, usually when the cabin temperature reaches what you have entered into the AC settings.

What you will notice with this symptom though is that this cut off will happen far quicker and far more frequently. It will also often have no connection to the actual temperature inside the cabin of the vehicle, so you could see the AC cutting out even as you are roasting in a hot car or truck.

That’s because it’s not actually cutting out because it is doing its job. Instead it is because the AC Pressure Switch is giving incorrect readings to the AC control. That in turn stops it working properly – and leaves you sitting in a puddle of sweat in the drivers seat.

What To Do Next?

If you are noticing any of these symptoms then get your car into a pro garage as soon as possible. The AC pressure switch plays such an important role in the operation of the AC system, and yet is at the same time a component that is quite vulnerable to damage.

When it has failed, or if it already failing, it will therefore present with symptoms that are pretty easy to detect. This is especially true if, as we pointed out above, you are used to the way that that AC normally operates.

It is also worth remembering that one of the main reasons the AC Pressure Switch is there in the first place is to protect the Air Conditioning system, in particular the compressor, from damage.

We would therefore strongly suggest that if you do notice any of these symptoms, you don’t use the AC at all until the problem has been investigated and resolved. This will prevent any damage to the compressor or AC system itself that, trust us, will cost a lot more to repair or replace than a simple AC Pressure Switch!

Originally posted 2023-10-06 19:17:26.

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