How to Fix a Frozen AC Unit Outside?
If you think about it, a frozen AC when it’s ultra hot outside is peak irony.
However, as it turns out, ice buildup on AC outdoor units is one of the most common AC problems people encounter. Ice formation on the evaporator coils can affect the airflow and heat exchange, resulting in discomfort.
If left unattended, it can put excess strain on the compressor, causing serious damage to your HVAC system. A compressor replacement can set you back around CAD 1,700 to CAD 3,300.
On the bright side, in most cases, troubleshooting a frozen outdoor AC unit is fairly straightforward and DIY-friendly if the culprit is dirty air filters. All you have to do is replace them.
On the not-so-bright side, there could be plenty of other reasons why your outside AC unit is freezing up, from pinhole refrigerant leaks to faulty blower motors. These serious issues demand expert help.
In this post, we will discuss the most common reasons behind ice buildup on outside AC unit and how to unfreeze it.
Signs of a Frozen AC Unit
Apart from the very obvious visual cue of ice on any part of the outdoor unit, here are two other signs that your AC is in trouble:
- A hissing sound coming from the unit.
- Lack of cool air even after the AC has been on for a good few minutes. Put your hand in front of the supply vents. If you feel warm air coming out of it, look for ice buildup on the outdoor unit.
What to Do If Your Outside AC Unit is Frozen?
Okay, the first thing you need to do when your AC is frozen is thaw it out.
Follow the instructions below to defrost your frozen AC unit outside:
1. Turn Off the AC
Not an easy thing to do when it’s burning outside. But keeping a frozen AC on can cause compressor overload, leading to costly repairs, or worse, a full replacement.
Immediately switch off the AC unit at the thermostat and the circuit breaker.
2. Change the Thermostat Setting
Set the thermostat from “COOL” to “OFF” so that the system does not continue sending cold refrigerant to the outdoor unit. Keeping it on will only exacerbate the freezing issue.
3. Turn the Fan On
Change the fan setting on your thermostat to “ON” (not “AUTO”). This will allow the indoor fan to blow warm air continuously over the evaporator coils. This helps speed up the defrosting process.
4. Wait for the Ice to Melt
Wait for the ice to melt naturally. This process can take anywhere from an hour to a whole day, depending on the extent of the freezing. If the ice doesn’t melt even after 24 hours, please contact an HVAC technician immediately.
While you are waiting for the ice to melt, do keep an eye on the following as well:
- Condensate Drain: Check the condensate drain line for clogs. As the ice melts, water will flow into the drain pan and then out through the drain line. If the line is blocked, it can cause water to back up and overflow. If you see a clog, please clear out the condensate line.
- Drain Pan: Make sure that the drain pan is not overflowing. If it is, place towels around the unit to absorb any excess water and prevent damage to flooring or surrounding areas.
Important: Turn your AC back on only when all the ice is gone and both the indoor and outdoor units are completely dry.
Common Reasons Why Your AC Unit Might Be Freezing Up
Thawing the AC is only a temporary solution. The problem can come back if it’s caused by a serious mechanical issue.
Whether it’s a simple case of a clogged air filter or something as serious as a refrigerant leak, only a thorough diagnosis can tell.
Here’s how to look for the underlying cause:
1. Restricted Airflow
What to Look For: Check your air filter, coils, and vents. Is the filter clogged with dust and wet to the touch? Is there any furniture or curtains in the way of the vents? Are the evaporator coils and surrounding parts full of dust?
What It Means: When airflow is restricted due to dirt buildup on the filter or evaporator coil itself, less warm air passes over the evaporator coil. This causes the coil to drop to freezing temperatures. No warm air equals no heat absorption. The result is ice formation on the outside AC line.
Solution: Can’t remember the last time the AC filters were changed? Then it has probably been too long and you should change them quickly. If the vents and evaporator coils are dirty, clean them thoroughly, including the cooling fan fins.
2. Refrigerant Leak
What to Look For: Check if your AC isn’t cooling as well as it used to or if it takes longer to reach the desired temperature. If you have an electronic leak detector on hand, then great. Otherwise, you can use a leak detection spray. We don’t recommend bubble testing due to the high chances of false negatives.
What It Means: The most common cause of ice formation is low refrigerant levels due to leaks in the system. If your air conditioner has a leak, the amount of refrigerant (the cooling agent) inside the system will gradually decrease. The low refrigerant charge will cause the system to overwork. This can cause it to produce excessive moisture.
This extra moisture can freeze on the evaporator coils (inside the unit) if the system is cold enough. If the outdoor condenser coils are also frozen, it is because the system is extremely overworked due to a leak.
Solution: A tiny leak is hard to detect and even harder to fix on your own. So, if this is what you suspect, call for professional help.
3. Collapsed Ductwork
What to Look For: Visually inspect your ductwork, especially in less accessible areas like attics or crawl spaces. Look for sections that appear crushed, bent, or flattened.
What It Means: When ductwork is collapsed or obstructed, it restricts the flow of warm air to the evaporator coils. If not addressed on time, this can result in damage to the AC system, including the compressor and fan motors
Solution: If you find a section of ductwork that’s collapsed or compromised, it needs to be repaired or replaced. This is usually a job for an HVAC technician, as improper handling could cause more damage.
4. Malfunctioning Blower Motor
What to Look For: Listen for unusual noises from the blower motor, or notice if airflow from your vents is weaker than usual. A weak blower motor usually makes a hissing sound.
What It Means: The blower motor is responsible for pushing air over the evaporator coil. If it’s not working correctly, the coil won’t get enough airflow, causing it to freeze. This can be due to motor failure, worn belts, or electrical issues within the motor.
Solution: Inspect the blower motor and its components for any obvious issues like frayed belts or loose connections. However, since this involves electrical components, it’s best to have a professional handle the problem.
While you are checking under the hood for such mechanical issues, also make sure the filter dryer, expansion valve, and refrigerant lines are in good shape.
Not Sure What’s Wrong?
If you are unable to diagnose the problem yourself or defrosting the AC doesn’t make a difference, it’s time to call an HVAC technician for expert repair.
That said, prevention is better than cure, any day. To prevent icing issues and other HVAC troubles in future, schedule professional HVAC tune-ups once a year. This will not only keep your system running optimally but also help you keep your energy bills under control.
