Why Does My Mini-Split Smell?

Mini-splits are energy-efficient heating and cooling solutions for entire homes as well as garages, attics, basements, and home additions. Any place that doesn’t have ductwork can benefit from a ductless mini-split system. But, like any mechanical system, they will occasionally have problems. 

Do you find yourself wrinkling your nose when your mini-split air conditioner turns on? Your Mitsubishi mini-split shouldn’t smell like anything. Neither should any other brand of ductless mini-splits. In this article, we’ll explore why your mini-split AC unit or heating unit may be giving off an unpleasant odor and what to do about it.

Spoiler alert: you may have to call an HVAC technician for help.

If your mini-split smells musty, or as some people describe it, like dirty socks or a gym bag, you may have mold growth in the unit. This is more common with mini-split air conditioning units, which produce condensation as part of the cooling process.

If the condensation doesn’t drain properly, the moisture combined with dust and pet hair, for example, provides a welcoming breeding ground for mold. Dark and damp.

The cause for the mold may be a dirty or clogged mini-split air filter, poor drainage due to a clogged condensate line, poor drainage due to improper installation, and more. DIY mini-split installation can frequently result in poor drainage.

If you smell something like white vinegar when your mini-split is running, turn it off. This smell also described as a chemical smell, can indicate that one or more internal components are overheating. This could be due to electrical problems or other issues. Contact your HVAC company to schedule a service call.

If you’ve cleaned the filters and had an HVAC professional check your mini-split system and failed to find anything wrong, the smell may not be coming from your mini-splits at all. Keep reading to learn more.

If your mini-split smells like fish or has a foul odor, it could be a dead rodent or other animal that has died in your walls. It could also be that there is an animal carcass near your outdoor condenser unit.

If you can smell it when the mini-split system is turned off, it’s not the mini-split. See if you notice that the odor is stronger near a certain area. You may need to do some sleuthing to find the source. Also, check outside by the mini-split heat pump.

If you see a dead animal, wear gloves and use a large garbage back over your arm and put the carcass in, and then pull the bag right side out. Think of what you do with a doggy poop bag. Then dispose of the trash bag in an air-tight trash container or take it to the landfill/dump.

If the musty smell or vinegar smell is coming from the mini-split, your best bet is to clean the filters and call an HVAC professional to get to the root of the problem. Depending on the problem and the source of the smell, they may do several things, including:

• Clear a clogged mini-split condensate line.
• Re-mount a wall-mounted mini-split to ensure proper drainage.
• Install a mini-split condensate pump as needed. These are more common with mini-split ceiling cassettes which don’t rely on gravity for drainage like wall-mount and floor-mount units do.
• Check for a refrigerant leak and make repairs/recharge the unit.
• Seal the hole where the refrigerant lines come into your home if it wasn’t properly sealed during mini-split installation.
• Take apart the mini-split and professionally clean each component to remove mold growth, reassemble the unit, and test it.
• Replace components that overheated or recommend mini-split replacement.

A little maintenance goes a long way toward preventing problems with your ductless mini-split HVAC system.  Clean the reusable mini-split filters on each indoor ductless unit regularly - as often as every two weeks during peak usage. Whether you have one mini-split air conditioner or a multi-zone mini-split heating and cooling system, make filter maintenance a part of your cleaning routine.

If you let your filters get clogged, they can cause a lot of problems, including

• Water leaks
• Mold and mildew
• Musty or funky smell
• Cooling problems
• Heating problems
• System damage

In addition, check around your outdoor mini-split heat pump regularly. Remove any plant debris and trim shrubbery or other plants to keep them at least two feet away from the outdoor unit.  Clear snow away from on top of and around the unit in the winter.

We recommend biannual mini-split maintenance for Trane/Mitsubishi mini-split heating and cooling systems - once before the cooling season and once before the heating season. Once a year may be enough for a cooling-only system unless you use it year-round.

If your ductless system is still under warranty, we recommend scheduling with the mini-split installer you used. For best results, work with a Trane dealer that has extensive experience with ductless mini-split heating and cooling systems.

During the maintenance visit, the HVAC technician should:

• Thoroughly inspect and clean the system including:
  • Outdoor ductless heat pump
  • Indoor mini-split units
  • Condensate drain line and mini-split condensate pump if applicable

• Test the ductless system for effective operation.
• Check for refrigerant leaks.
• Check electrical connections.
• Make minor mini-split repairs.

If your mini-split has a bad smell or you need seasonal maintenance, schedule it now.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Kimberly Sexton, Senior Systems Engineer

Understanding Your Trane/Mitsubishi Mini-Split Remote

Do Mini Splits Have Filters?

Do Mini-Splits Turn Off When Temperature is Reached?

Mini-Split Compressor Not Turning On

Mini-Split Leaking Water

Mini-Split Not Cooling

Mini-Split Not Working In Heat Mode

Mini-Split Refrigerant Issues

What Size Mini-Split Do I Need?