How to clean coils on hvac unit

To clean coils on an HVAC unit, turn off power and spray the coils with commercial coil cleaner, then rinse with water after the cleaner foams and dissolves dirt buildup. This guide covers cleaning both outdoor condenser coils and indoor evaporator coils to restore proper heat transfer and improve system efficiency.

What You’ll Need

• Garden hose with spray nozzle
• Soft-bristle brush
• Screwdriver set
• Flashlight
• Commercial coil cleaner
• Safety glasses
• Work gloves
• Shop rags

Step-by-Step Guide

Step 1: Turn off power and access the coils

Switch off the HVAC system at the thermostat, then turn off power at the electrical disconnect switch near the outdoor unit and at the main breaker panel. For the outdoor condenser unit, remove the top fan grille by unscrewing the fasteners and carefully lifting it out with the fan motor attached. For indoor evaporator coils, remove the access panel on your air handler or furnace using a screwdriver.

Warning: Never work on HVAC equipment with power connected, as motors and electrical components can cause serious injury.

Step 2: Inspect and prepare the coils for cleaning

Use a flashlight to examine the coil surfaces for dirt, debris, and bent fins. Note areas with heavy buildup that will need extra attention. Clear away any leaves, grass, or large debris from around the coils by hand. Check that the coil fins are not severely bent, as this will require professional straightening tools.

Step 3: Apply coil cleaner to the dirty surfaces

Spray commercial coil cleaner evenly across the coil surface, working from top to bottom to ensure complete coverage. Focus on heavily soiled areas but avoid oversaturating electrical components nearby. The cleaner will foam and begin dissolving grease, dirt, and organic buildup on contact. Allow the cleaner to work for the time specified on the product label, typically 5-10 minutes.

Step 4: Rinse and remove loosened debris

Rinse the coils thoroughly with a garden hose, spraying from the inside of the coil outward to push debris away from the fins rather than deeper into the coil. Use gentle water pressure to avoid bending the aluminum fins. For stubborn spots, use a soft-bristle brush to gently scrub the fin surfaces, then rinse again until water runs clear.

Warning: Avoid using high pressure settings that can bend delicate coil fins and reduce heat transfer efficiency.

Step 5: Dry and restore power to the system

Allow the coils to air dry completely before reassembling the unit, typically 15-20 minutes in normal conditions. Replace all access panels and fan grilles, ensuring fasteners are properly tightened. Restore power at the disconnect switch and main breaker, then turn the system back on at the thermostat to verify normal operation.

Frequently Asked Questions

How often should I clean my HVAC coils?

Clean outdoor condenser coils at least twice per year, typically in spring and fall. Indoor evaporator coils should be cleaned annually or when you notice reduced airflow or ice formation on the coil.

Can I use household cleaners instead of commercial coil cleaner?

Avoid household cleaners as they can damage coil materials and leave residues that attract more dirt. Commercial coil cleaners are formulated specifically for aluminum fins and copper tubing used in HVAC coils.

What happens if I don't clean dirty coils?

Dirty coils reduce heat transfer efficiency, causing your system to work harder and use more energy. This leads to higher utility bills, reduced comfort, and potential compressor damage from overheating or liquid refrigerant returning to the compressor.

Is it normal for coil cleaner to foam heavily?

Yes, foaming action is normal and indicates the cleaner is working to break down dirt and organic buildup. Heavy foaming usually occurs on very dirty coils and will subside as the cleaning agents dissolve the contamination.

Should I clean both indoor and outdoor coils at the same time?

While not required, cleaning both coils during the same maintenance session ensures optimal system performance. However, outdoor coils typically need more frequent cleaning due to exposure to environmental contaminants like pollen, dust, and lawn debris.