A frozen central air conditioning unit is an annoyance that can turn into an expensive problem if you don't handle it properly. You need to thaw the unit before you can use it or risk causing serious damage. The thawing process takes time, giving you a perfect opportunity to catch up on maintenance tasks like changing the unit's air filter. Doing so should prevent the air conditioner from freezing again after you defrost it unless you have another issues, such as a refrigerant leak, that requires a professional repair.
Defrosting a Central A/C Unit
Step 1: Turn Off the A/C
Turn your air conditioner off at the thermostat, and leave it to thaw for several hours. If your unit gives you the option to do so, turn on the fan while leaving the cooling off. This shortens defrosting time and helps dry out the unit. The amount of time your unit needs to defrost will vary based on the temperature and how badly frozen the unit was. You could have to wait up to 24 hours before using your air conditioner again.
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Step 2: Turn Off the Circuit Breaker
Turn off the circuit breaker that feeds the A/C once it's thawed so you can safely perform a few basic maintenance tasks.
Step 3: Replace the Filter
Remove and replace the unit's air filter to prevent the unit from freezing again. Clogged filters block airflow and can cause freezing. The air filter will be inside the air conditioner's indoor unit or behind the cold air return.
Step 4: Clean the Evaporator
Clean your air conditioner's evaporator by carefully vacuuming away any debris using your vacuum's soft brush attachment. You'll find the evaporator coil in the indoor part of your air conditioning unit near the main duct. Made of copper piping, it sits in an A-frame configuration at the top of the air conditioner. In some cases, the copper pipes are covered in metal fins. Depending on your unit's construction, you may not have access to the evaporator. If you can access your evaporator coil, your air conditioner user manual should tell you how. If you don't, simply move on to the next step.
Step 5: Clean the Condenser
Grab your vacuum cleaner and head outside to clean your air conditioner's condenser. The A/C condenser consists of a series of delicate metal fins and is located in the portion of your air conditioner that sits outside. You'll have to remove the unit's outer cover to reach the condenser. Vacuum your condenser using the same brush attachment you used to clean the evaporator. Be very gentle, as the metal fins of the condenser are delicate and easily bent.
Step 6: Clean Around the Unit
Pull any weeds or grasses that are growing around your outdoor condenser unit. If any bushes are present, trim them back to leave at least 12 to 18 inches of clear space around the condenser on all sides.
Step 7: Clear Indoor Vents
Head back inside and take a tour of your home. Make sure that no curtains, furniture pieces, or other items are blocking your air conditioning vents and that they're all in the open position.
Step 8: Turn the Power On
Restore power to your air conditioner by flipping the circuit breaker. Turn the unit on, and enjoy the cool breeze.
When to Call a Pro
If your unit freezes again, call an HVAC technician. The problem could be a refrigerant leak, which requires a professional repair.