It’s a common misconception that if you turn the thermostat too low, you’ll freeze up your air conditioning system. That can contribute to your air conditioner freezing up, but it’s not the underlying cause.
If it freezes up once or twice, that’s not terrible news. But if it’s freezing up once a week, that indicates a systemic issue. There are four common reasons for air conditioners to freeze up, and having an idea of what’s causing yours to do that can help you figure out what next steps to take.
Reason 1 – Insufficient air flow
Your air conditioning system needs to have air flowing through it to work properly—specifically, across the evaporator coil. If it’s not blowing air over that coil, the heat exchange isn’t working right. That lack of air flow causes it to work harder and makes it difficult for it to remove heat from the home, causing ice to form on your unit.
Reason 2 – Refrigerant issue
Your unit cannot function without refrigerant. It’s what removes heat from the air in your home. A frozen unit could indicate that the refrigerant is low, or that the pressure in your system is off (usually because of a leak).
Reason 3 – Temperature fluctuations
Air conditioners are designed to work within a certain temperature range. When there is high humidity and a wide temperature range outdoors (like during most Spring months), those conditions can create a big pressure drop within your system when it turns on. That makes it freeze up.
Reason 4 – Mechanical problems
If there’s a kink in your refrigerant line, that restriction can create a problem, just like a kink in your garden hose makes it difficult to water your plants. Or if your air filters or air ducts are very dirty, that can restrict airflow and make it difficult for your system to run properly.
All four of these reasons come back to the pressure in your system and whether it allows your refrigerant to flow smoothly between your air conditioner and your furnace. When that flow is disrupted, your air conditioner doesn’t work properly and can freeze up.
What can you do?
Turn your air conditioner off! It’s not working when it’s all frozen up.
Check your evaporator coil and condenser coil, if you’re comfortable doing so. If it’s frozen, you’ll be able to see it from a distance.
Look for airflow restriction. Are your vents closed? Is there enough space around your air conditioning unit to allow air flow?
Change your air filters if they are dirty.
Check for really dirty air ducts— if they’re full of gunk, that will restrict airflow too.
If your air conditioning system is repeatedly freezing up, that can ruin your compressor. And once your compressor’s out of action, you pretty much need a new unit.
Some companies might install a new compressor, but we don’t recommend it—it’s like installing a new engine in a car. By the time you need to replace the engine, there are usually so many other issues with the car that it makes more sense to just buy a new one.
It’s important to pay attention to your air conditioner freezing up as early as you can. While it is expensive to replace your air conditioning system, a small refrigerant leak may only cost you a few hundred dollars.
If you’ve done all you feel comfortable with, and your air conditioning unit is still freezing up, you may want to call a professional to diagnose the underlying problem before it causes further damage.