If you’ve got a musty smell coming from your air conditioner or you’re worried about organic growth around your indoor AC coil, you may have seen a simple DIY solution online: spray it with bleach.

Please don’t.

Bleach might be something you use to clean around the house, but your air conditioning system is a completely different environment. Your indoor coil contains metal components, sits directly in the path of the air circulating through your home, and is surrounded by other parts that weren’t designed to be sprayed with household bleach.

I recently came across a video recommending bleach as part of cleaning an AC system, so I broke it down from an HVAC professional’s perspective.

​Watch my full reaction below:

Why Do People Recommend Bleach for an Air Conditioner?

I understand where the idea comes from.

Your air conditioner removes moisture from the air as it operates. Warm, humid air from your home passes across the cold indoor evaporator coil. Condensation forms on that coil and drains into the condensate pan before leaving your home through the drain line.

Here in North Carolina, we deal with plenty of heat and humidity. That means the indoor portion of an air conditioning system can spend a lot of time damp during cooling season.

Combine moisture, darkness and dirt or other material that gets past the filter, and you've created conditions where organic growth can develop.

So somebody sees that growth and thinks, “Bleach kills stuff. I'll spray some bleach on it.”

That's where we have a problem.

Your AC Coil Isn't a Shower or Kitchen Counter

An evaporator coil is a piece of mechanical equipment.

Depending on the system, you've got aluminum, copper and other materials and components in and around that coil assembly. Using a chemical that wasn't intended or approved for those components can create problems of its own.

Bleach is corrosive. I don't want homeowners spraying it onto an evaporator coil, into the equipment cabinet, or around electrical and mechanical components.

And remember where this equipment is located.

The air your family breathes is moving across that coil.

That's another reason I'm not a fan of randomly spraying household chemicals inside an HVAC system.

When an evaporator coil actually needs to be cleaned, we use products and procedures intended for HVAC equipment.

What If Your AC Smells Musty?

This is where we need to fix the cause, not just cover up the symptom.

Your air conditioner naturally produces condensation. That water should collect properly and drain away from the system.

If you're getting a recurring musty smell, excessive organic growth, standing water or other moisture problems around the equipment, I want to know why it's happening.

Is the condensate drain restricted?
Is the drain pan staying wet?
Is the coil excessively dirty?
Is the air filter doing its job?
Is there another source of moisture?
Are we dealing with an indoor air quality issue?

Those are the questions we should be asking.

Spraying bleach might make you feel like you've treated the problem, but it hasn't necessarily addressed what caused the condition in the first place.

And around here, band-aid repairs are never acceptable.

Should You Pour Bleach Down Your AC Drain Line?

You'll also find plenty of advice online telling homeowners to regularly pour bleach into their AC condensate drain.

I would be careful with that advice as well.

Different systems, drain configurations and materials can require different maintenance procedures. I don't like giving every homeowner a blanket recommendation to pour a strong chemical into an HVAC system without knowing how that particular system is designed.

If you're having repeated condensate drain clogs, the better question is:

Why does this drain keep stopping up?

It may simply need proper cleaning and maintenance, or there could be another issue contributing to the problem.

What CAN a Homeowner Safely Do?

There are plenty of things homeowners can do themselves that really do help their air conditioner.

Change your air filter regularly. A dirty filter restricts airflow and allows more contamination to accumulate where you don't want it.

Keep your return-air grilles clear. Don't block them with furniture, boxes or other household items.

Look around the indoor equipment for water. If you notice standing water, wet insulation, staining or water where it shouldn't be, don't ignore it.

Keep the outdoor unit clear. Grass clippings, weeds, leaves and debris can restrict airflow through the outdoor coil.

Pay attention to changes. New smells, unusual noises, longer run times and changes in comfort are often your HVAC system telling you something has changed.

Those are good homeowner habits.

Spraying bleach onto an evaporator coil isn't one of them.

What About UV Lights?

If recurring organic growth on the indoor coil is the concern, there are products specifically designed to address that environment.

One option we use is a UV system positioned to shine ultraviolet light on the indoor coil.

Instead of waiting for growth to develop and repeatedly trying to clean it away, UV treatment can help prevent organic growth in the area where it's installed.

That's a much different approach from opening up your air conditioner and spraying household bleach inside it.

Not every home needs UV, either. The right solution depends on what we're actually finding inside the system.

Be Careful With HVAC Advice You See Online

This is one reason I've started reacting to more HVAC videos online.

There is some good information out there.

There is also advice that sounds good in a 30-second video but leaves out some pretty important details.

I've been working in the HVAC industry for more than 20 years, and one thing I've learned is that the easy answer isn't always the right answer.

Before you pour, spray, cut, bypass or modify something on your heating and cooling system because somebody online told you to do it, find out what that recommendation could do to the rest of the system.

Sometimes a $5 DIY solution can turn into a much more expensive repair.

Here’s the Takeaway

Don't spray household bleach on your AC evaporator coil.

If you've got a dirty coil, recurring musty odors, organic growth, drainage problems or excessive moisture around your HVAC equipment, let's figure out what's causing it.

Fix the cause instead of treating the symptom.

If you're in Fayetteville, Pinehurst, Laurinburg or the surrounding Sandhills area and you're concerned about your air conditioner or indoor air quality, Simmons One Hour Heating & Air Conditioning can help.

Always On Time Or You Don’t Pay A Dime!®

​And if you've got an HVAC question and aren't ready to schedule a visit, you can also ask Derek AI on our website at SimmonsOneHour.com. I've loaded it with more than 20 years of my HVAC experience so homeowners can get answers to their heating and cooling questions 24/7.