Everyone who has walked to their indoor unit on a hot summer day and noticed a block of ice forming on the unit’s pipes or coils, will understand the frustration. One of the most frequent issues that homeowners experience in the GTA, Mississauga, Oakville, Hamilton and beyond during the cooling season is an ac freezing up and it can wreak complete havoc on your home’s comfort system.
On the face of it, if you’re supposed to keep the temperature down, a smidgen of ice should be a positive! Not at all. When ice begins to build up on your unit, it’s an indication of an issue. If not taken care of, it can harm your system, increase your energy bills and transform a minor ac problem into a costly repair.
We explain here the reasons why your air conditioner freezes, what you can do to fix it immediately, and when you should call a professionally licensed HVAC expert. If you are in Brampton, Etobicoke, Cambridge, Milton and anywhere in Southern Ontario you’ll find that this article is for you.
How Does an Air Conditioner Actually Work?
It is helpful to understand what your AC is doing under the hood before getting into the cause(s) of the problem. This system circulates warm air through your house and brings it in contact with a set of cold coils containing refrigerant. That refrigerant sucks up the heat and you get cool conditioned air.
The correct operation of such a process requires proper balance of the flow rates, pressures and temperatures of both the air and the refrigerant. If any of these factors are disturbed, the evaporator coil can freeze, which will allow moisture in the air to freeze on the surface of the coil. The thin layer of frost can soon grow into a thick layer of ice that smothers the system, this is referred to as air conditioner “frozen coils.
Top Reasons Your AC Unit Keeps Freezing Up
1. Restricted Airflow The Number One Culprit
The most common reason for an ac unit freezing up is poor airflow over the evaporator coil. If the warm indoor air flow stops, the coil will become extremely cold. If this flow is prevented, the refrigerant has less ability to absorb heat and temperatures drop drastically below freezing.
Typical blockers of airflow are:
- Dirty or clogged air filters (change every 1-3 months) Closed or blocked supply vents Furniture, curtains or boxes obstruct return air grills Dirty evaporator coils
- The solution can sometimes be as straightforward as changing out a clogged filter. If you are a homeowner in Toronto’s GTA and have your AC system run during the wet and humid summer season in Ontario, it is strongly recommended that you check the filter every month.
2. Low Refrigerant Levels A Leak You Need to Fix
Refrigerants are not used up, unlike fuel. When a system is low on refrigerant, it is due to a leak somewhere. As the refrigerant is depleted, so is the pressure, allowing the remaining R-134a to be refrigerated even more below its normal operating temperature. This directly results in ac frozen coil problems.
Symptoms of a refrigerant leak can be hissing or bubbling noises, the development of ice on the ac lines, frozen or refrigerant pipes, decreased cooling ability and an increase in hydro bills. Just re-filling refrigerant with no attempt to fix the leak is a band-aid. A furnace technician who is trained and licensed must find the leak, seal it and refill the system.
3. A Malfunctioning Blower Fan
Your blower fan is responsible for pushing air across the evaporator coil. A fan motor that is failing, has dust build-up or is not moving the air fast enough will not move sufficient warm air across the coil. This causes the condensation to accumulate faster than it can drain eventually leading to ac pipes freezing and ac lines freezing throughout the system.
If you hear unusual noises from your unit, like grinding, squealing, or rattling, this may mean that your fan is having an issue. A faulty blower is not something that can be fixed by a handyman, it needs to be diagnosed and fixed by a licensed HVAC technician.
4. Dirty Evaporator Coils
Dust, pet hair and debris will cover the evaporator coil over time. This coating of dirt is like insulation; it does not allow the coil to absorb heat as it should. This then causes the coil to become cold and cold and finally freezes your system! Regular coil cleaning is a standard part of annual ac service and is one of the best ways to avoid this issue.
5. A Faulty Thermostat
If the AC periodically only freezes at night or during cooler times, it could be an issue with the thermostat. The thermostat can malfunction and not communicate to the system when to turn it off at the correct temperature, so the system will keep running. Cooler night time temperatures and longer run cycles may cause ice to build up on coils. If that doesn’t solve the issue, use new batteries first; if it doesn’t work, the thermostat may need to be replaced.
6. Running Your AC in Cool Outdoor Temperatures
In Ontario, we do have cool nights in summer time. The reason is that the air conditioner’s refrigerant pressure decreases when the outside temperature is below approximately 15°C (60°F) so it freezes. If nights are cool, consider using fan-only or even unplug your system!
What Are the Signs That My AC Is Frozen?
Catching a freeze early can save you from a bigger ac repair near me. Watch out for these telltale signs:
- Warm air blowing from vents even though the AC is running
- Visible ice on the ac pipe frozen or refrigerant lines
- An ac unit has ice on the outdoor condenser or indoor air handler
- Water pooling around your indoor unit (from melting ice)
- Reduced or weak airflow from supply vents
- Unusually high energy bills
If you notice any of these signs, don’t ignore them. A frozen AC that’s left running can damage the compressor, one of the most expensive components in the entire system.
Frozen AC Causes and Solutions
| Common Cause | Possible Solution |
| Dirty Air Filter | Replace the filter and restore proper airflow |
| Blocked Supply or Return Vents | Open and clear all vents and registers |
| Dirty Evaporator Coil | Schedule professional coil cleaning |
| Low Refrigerant Levels | Repair the leak and recharge the system |
| Faulty Blower Fan | Have the motor and components inspected |
| Thermostat Problems | Test, recalibrate, or replace the thermostat |
| Running AC During Cool Weather | Avoid running the system below 15°C outdoor temperatures |
While some issues can be fixed by homeowners, refrigerant leaks, electrical problems, and blower motor failures should always be handled by a certified HVAC technician.
What Should I Do Immediately If My AC Is Frozen?
If you discover ice on your unit, here’s what to do right away:
- Immediately disable the cooling mode. Set the thermostat to “Fan Only” or just turn it off. If the frozen AC continues to operate, the compressor will burn out.
- Wait for the ice to melt completely. While this process can be as quick as a few hours or up to a full day, depending on the amount of ice accumulation. Cover the indoor unit with towels to absorb any water that drips.
- Replace your air filter. If it’s dirty, the most common cause is a clogged filter; replace the filter.
- Check your vents. Make sure all supply and return air vents are open and unblocked.
- When thawed, restart the system and observe closely. When the ice begins to re-form, it’s time to call a professional.
Do not try to chip away at the ice manually this can damage the coils and make matters worse.
How Do I Prevent My AC From Freezing in the Future?
A prevention call is ALWAYS cheaper than a repair call. Here are some of the top practices for keeping your system ice-free throughout the season:
- Replace air filter every 1-3 months, more frequently if you have allergies or pets
- Ensure all supply vents and return air registers are open and unobstructed and have a yearly hvac repair or tune up schedule in the spring before the cooling season starts.
- Keep the thermostat at 20°C (68°F) or more at nighttime
- If you see decreased air flow or efficiency, book a professional coil cleaning.
- Do not operate AC with the outdoor temperature lower than 15°C
Can I Fix a Frozen AC Myself, or Do I Need a Professional?
Changing a dirt filter, unclogging blocked vents and allowing filters to thaw are definitely homey tasks. However, if you still get ice even after you’ve worked on the fundamentals, it probably needs a doctor’s diagnosis.
Any leak in the refrigerant, a problem with the blower fan motor, electrical problems or damaged coils all need a licensed HVAC technician who is equipped and certified to handle the problem. This is not a DIY job, in Ontario to handle refrigerant properly is illegal.
Looking for a hvac repair near me or fix air conditioner services? Be sure to be calling a legitimate company that has local knowledge and experience in Southern Ontario’s climate.
How Much Does It Cost to Fix a Frozen AC in Ontario?
The cost will depend on the underlying cause. It is simple and inexpensive to replace a filter. The cost of a refrigerant recharge ($300-$800 or more) depends on how much refrigerant is lost and the type of refrigerant used. The cost of replacement for the blower motor could be between $250 and $600. When the compressor has been frozen for an extended period, expenses can escalate rapidly – hence the importance of early detection.
The first step is to get a diagnosis from a trusted local company. Good HVAC firms will provide you with a clear quote prior to performing any work.
AC Maintenance Checklist to Prevent Freeze-Ups
The best way to avoid a frozen air conditioner is through regular maintenance. A few simple preventative steps can help improve efficiency, lower energy costs, and reduce the risk of unexpected breakdowns.
✓ Replace air filters every 1–3 months
✓ Keep supply and return vents open and unobstructed
✓ Schedule professional AC maintenance every spring
✓ Clean debris from around the outdoor condenser unit
✓ Monitor your energy bills for unusual increases
✓ Address weak airflow or cooling issues early
✓ Keep thermostat settings reasonable during cooler nights
✓ Have evaporator coils inspected and cleaned when necessary
✓ Check for signs of water leaks or excess condensation
✓ Avoid running the AC when outdoor temperatures are below 15°C
Following these maintenance practices can help extend the lifespan of your system and significantly reduce the chances of dealing with frozen evaporator coils during the summer.
Your Local HVAC and Home Services Experts: BOS Plumbing and Drains
If your ac freezing up issue is not just a filter change, then you require a team that you can rely on. For more than 20 years, BOS Plumbing & Drains has been providing homeowners and businesses with highly dependable, trustworthy and professional home plumbing and drainage solutions in Southern Ontario.
From Mississauga to Oakville, Hamilton to Milton, Niagara to Cambridge, Brampton to Etobicoke, BOS is there to help you with your needs.
They provide all sorts of home comfort and maintenance services, such as:
Plumbing repair and install service, drain cleaning and hydro-jetting, air conditioner repair and maintenance, HVAC repair and tune up service, plumbing and drain emergencies, water heater install and repair
The BOS team has 20 years of practical experience in Ontario’s climate extreme humid summers, extreme winters, and everything in between. If you need BOS Plumbing and Drains to come out and repair your HVAC unit before hot summer weather hits or you have a problem with your air conditioner, we’re available to come out and help you out as soon as possible.
When ac coils are freezing up, frozen air conditioner line issues, or any other cooling system problem, BOS technicians have seen it all and fixed it all. Their transparent pricing and expert service has earned them the trust of many around the GTA and beyond.
When Should You Call an HVAC Technician?
Some frozen AC problems can be fixed by changing a dirty air filter or by opening blocked vents, but some problems can only be fixed by professional AC repair services. Timely HVAC professional contact can assist you in preventing additional damage and also pricey repairs.
If ice builds up again after the system has fully thawed out, if the air conditioner is not cooling the air as it should, or if hissing noises are heard, which could signal a refrigerant leak, a licensed HVAC professional should be called for assistance. Other indicators of trouble are poor airflow, strange sounds, burning smells from the electrical components, or water seeping through the air conditioner unit’s base.
Professional technicians are trained to use diagnostic tools and equipment to correctly identify refrigerant problems, electrical issues, blower motor problems, and damaged parts. When you’re not sure what is causing your AC to freeze, it is often the fastest and cheapest way to proceed is to schedule an inspection.
The Bottom Line: Don’t Ignore a Frozen AC
When an air conditioner freezes, it’s no ordinary occurrence. It may seem like a minor inconvenience today, but can be a big problem and a costly issue in Ontario during the hot summer months. Fortunately, most freeze ups can be avoided with routine maintenance and some care.
Do the basics: change your filter, open the vents, and allow the system to thaw. If it’s still recurring, call a reputable air conditioner repair technician that is familiar with Ontario homes. From Mississauga and Oakville, to Hamilton and Brampton, and beyond, BOS Plumbing and Drains has the staffing, expertise, and equipment needed to keep you cool and comfortable throughout the season.
Don’t wait for a complete breakdown schedule for your AC inspection today.