Air Conditioner Freezing Up: Here Are the Causes and Fixes

air conditioner freezing up

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Has your air conditioner frozen up? It always seems to happen at the very hottest time, leaving you in a bit of a panic, forced to scramble and sweat and try to figure out what in the world happened – and without even your air conditioner to keep you cool!

Worrying is understandable, since air conditioners – and air conditioner repairs – can be very expensive. But don’t panic yet – it might be something quite simple and inexpensive. So let’s get into the most common causes of an air conditioner icing up, and what you can do to fix it!

Why Do Air Conditioners Freeze Up?

The number one reason an air conditioner freezes up and stops working is because of insufficient air flow

An air conditioner uses an evaporator coil which holds very cold refrigerant, and this coil cools the air in your home so that the AC’s fans can distribute the cooler air into your space.

The evaporator coil cools warm air, but it also needs that warm air to keep functioning properly. If there is not enough of this air flowing across the coil, it will get too cold, and the evaporator coil will freeze up, causing the whole system to stop working.

There are a lot of different reasons this can happen:

Collapsed or Blocked Ducts

If any of the ductwork, which brings your home’s warm air into the air conditioner, is blocked up, that warm air can’t reach the evaporator coil, which will in turn become too cold and freeze up.

  • This is more of a concern with central air, and does not really apply to in-window or portable ACs.

Dirty Air Filters

Dirty air filters can also greatly impede the flow of warm air to the evaporator coil, and you should make sure to clean or replace those coils every three months or less, depending on the amount of dust in your home.

Besides, clean filters will keep your home’s air cleaner and healthier!

  • This applies to all types of ACs.

Other Air Blockages

Basic window-mount or portable air conditioners will not have extensive ductwork – portables may have a single air hose to allow the warm air to go outside – but they both will have vents to let warm air into the evaporator coil, and these vents need to be given proper clearance and not blocked by anything – curtains, for example, can cause problems.

  • An important and easy thing to check and fix with, again, window-mount/through-wall and/or portable air conditioners.

Blower Motor Problems

Even if your filters are clean, and there is no blockage to ducts or vents, there are still reasons why an evaporator coil may not get the warm air it needs to keep from freezing, and the main problems will lie with the blower motor, which works to move that warm air.

This is a much less common issue, which can be caused by insufficient voltage reaching the motor (because of faulty wiring, electrical or electronic problems or other things), or simply a bad or worn out motor.

  • This can be an issue with all kinds of ACs – central air, portable, in-window and others – and is the first problem we’ve mentioned where you should consider getting professional consultation and repair.
air conditioner freezing up

What Else Could it Be? Other Causes of Air Conditioners Freezing Up

Cold Air

We’ve looked at reasons why warm air might not be reaching the evaporator coil, but there might be another – if much less common – reason your AC keeps freezing, and that is that the air blowing across the evaporator coil is itself too cold.

This is a lot less common because it means that the air in your home is already cold, and so it would be highly unlikely that you are running the air con in the first place! 

When this does happen, though, it is usually a simple matter of turning the AC off completely and letting it thaw out in its own time. Really, though, it is crucial to shut down the AC immediately, as to prevent any damage to the compressor, evaporator coil, motors or other parts.

If you ever notice that the AC unit is turning on by itself when it is too cold inside – assuming you yourself aren’t silly enough to use it when it’s already freezing in the house – you might have a problem with a faulty thermostat or control unit – or poltergeists. Either way, call an expert for a help.

Faulty Compressor or Evaporator Coils

Refrigerant that cannot be compressed and heated up, too low of refrigerant levels, leaking refrigerant lines, low pressure and other issues might lead to your AC unit freezing up, and these can be due to broken tubes, a faulty or worn out compressor or a broken coil, among other things.

Any of these issues definitely need to be handled professionally – although if your AC is quite old already, it might literally be cheaper – or at least make a lot more sense – to purchase a new air conditioner instead – why throw good money after bad – or cold cash after a hot mess, for that matter?

Clogged Condensate Lines or a Faulty Condensate Pump

Evaporator coils create condensation – excess water – and this condensation must be moved away in order to prevent freezing. If the lines are clogged, or cannot for whatever reason cannot rid the coils of this excess water, the system may freeze over.

This may not be a difficult repair, but given the fragile – and expensive! – nature of the components involved, it is highly recommended to let an HVAC professional handle it.

Dirty Evaporator Coil

Less likely than other issues, and sometimes connected with the issue of dirty air filters (or the silly and unwise practice of running an AC with no filters in place), evaporator coils which get covered in dirt, dust or other stuff will not be able to get sufficiently warmed no matter how much warm air moves across them, and so will freeze up.

Again, though this isn’t difficult to deal with, these coils are expensive and fragile, and it is best to get a professional AC cleaning and maintenance.

So, what can you do about all of this?

How to Fix a Frozen Air Conditioner

If you’re already hot and bothered, and heading into yet another 90+ degree day, you’re not going to like this next bit – but remember, don’t kill the messenger!

You see, the internet is filled with “helpful” advice on what to do when your AC unit freezes up inside, how to unfreeze your AC system, how to get the cold air moving again – but much of it is unwise and possibly dangerous.

I personally would not use a hair dryer or any kind of heater to try to thaw the evaporator coils – for one thing, too fast of a temperature shift can cause them to crack.

And NEVER (sorry for shouting…) try to chip away the ice! NEVER (there I go again…)! This definitely will, 101 times out of a hundred, puncture the coils, and can lead to all kinds of other problems – and will cost more money than you can imagine.

So, what’s a poor, hot homeowner to do?

Step 1: Shut Down Everything 

Before you even try to deal with the situation, shut down the entire AC system, to prevent damage to motors, the compressor, the evaporator coil, the condensate pump, your wallet and other valuable bits. Really, first thing and right away!

Step 2: Let the Heat Work to Your Advantage

Here, as I’ve already intimated, I’m going against common internet “wisdom,” and possibly making myself a bit unpopular with you, gentle reader, but I do not advise trying to somehow thaw out your evaporator coil, or any other part of your AC system.

Really, any mechanical or physical attempts can seriously damage the fragile parts of the system – no matter how careful you are or how steady your hand – and fast or extreme temperature shifts can do the same.

So, yeah, sorry, it really is best to let the completely shut down air conditioner thaw out on its own – but in this heat, how long can that take, really?

Step 3: Find and Fix the Root Cause

Your natural (if slightly overheated) tendency is going to be to immediately turn everything back on and let the cold air flow as soon as you can see the ice is all gone, but if there is some problem that you haven’t seen or dealt with, this can also cause real and permanent damage – sometimes, even, things that didn’t break during the initial freeze and failure might well break during start-up and continuous running.

So, explore all of the possibilities, before you restart the system.

  • If you can see problems with the ductwork – especially blockages – and you can deal with them yourself, great!
  • If there is an obvious blockage or impediment to the flow of air into a window-mount or portable air conditioner – either to the air coming in or the air being moved outside – by all means remove it.
  • Replace, or at least thoroughly clean, the filters, whether they seem dirty or clogged or not – really, why not? Your lungs and your evaporator coil will thank you!
  • If you somehow determine that there are problems with the functionality of the blower fan, the condensate pump, the compressor or the evaporator coils and related tubing, unless you are a licensed HVAC technician (or fabulously and unconcernedly wealthy) call an expert.
  • Between fragile and expensive components, possibly dangerous chemicals and electrical shock (not to mention working without an air conditioner running!), trying to proceed on your own is a fool’s errand.
  • Also, if you simply cannot determine what’s wrong, or cannot find any blockages, impediments or other problems with air flow that you can easily fix yourself, call an HVAC technician and let them perform a complete diagnostic.

Step 4: Restart

If you have found a simple problem – blockages in vents or ducts or a very dirty air filter – and have been able to right the situation, you can restart your AC.

But please, if you notice ice building up again, or it’s not cooling well, or if there are any strange noises or other things you notice out of the ordinary, shut it down right away and get some professional advice.

air conditioner freezing up

Conclusion: Is it Worth It to Repair an Old Air Conditioner?

This is a good and frequently asked question – when should you fix, and when should you replace?

And of course there isn’t a simple and straightforward answer…

Central air conditioning is quite expensive, and while expert repair by a qualified HVAC technician can also be pretty pricey, it is usually nothing compared to replacing the whole system and reinstalling the new components.

Even in-window or portable air conditioners can be a bit expensive, and if your unit is not too old, and has been working well up to the freeze-up, it probably makes sense to get it fixed rather than throwing it out.

And of course if the repairs are as simple as unblocking air flow, it’s a no-brainer!

On the other hand, if your central air, or your smaller AC unit, has been having performance issues anyway – not really cooling like it used to, making weird noises or having other problems – it might be time to move on. After all, this repair may not be the last, and they tend to come more and more frequently as the end nears.

At any rate, you might find a HVAC specialist in your area who will give free, or low cost, estimates and informal diagnoses, and even just talking to an expert on the phone can reveal a lot of information about what may be wrong, how deep and serious the problem actually is, how much it might cost to fix – or replace – and what your next step is.

If you do decide to buy a new air conditioner, I really hope you will visit our site – Know the Flo – for information and excellent buyer’s guides – on air conditioners and all of your home heating and cooling needs.

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