Why Going on Vacation Can Lead to Mold Growth in Your Central Air Conditioner

July 21, 2014

Before leaving for vacation, most homeowners go down a checklist of “to-dos.” One of those to-dos includes turning off their central air conditioner.

No need to cool your home when you’re not there, right?


Turning the air conditioning off allows the humidity level to get too high (above 60%), which can hurt wood flooring, doors and cabinets.

Not only that, but high humidity will promote mold growth in your central air conditioner’s evaporator coil in the inside unit.  That’s bad news for anyone in your home with allergy or asthma issues.

Why does high humidity promote mold growth in the central air conditioner?

Mold spores easily reproduce when they have these 4 things:

  • Moisture
  • Food (dead organic matter like dust)
  • Darkness (UV light from the sun kills mold and other bacteria)
  • Warmer temperatures (80 degrees is best)

Your air conditioner’s inside unit already has 2 of these factors: darkness and food (dust often builds up on the evaporator coil when it’s never cleaned, and you don’t ;change the air filter, when it’s dirty).

So now all mold needs is moisture and warmer temperatures.

When you don’t run the AC for over 24 hours during a humid summer, condensation forms on the dirty evaporator coil and drain pan underneath. And the evaporator coil is now warm because there’s no cold liquid refrigerant running through it like usual.

Now all 4 factors are there. Say hello to mold growth!

Turn it up, but don’t turn it off

So if you do go on vacation, turn your temperature setting up. Just don’t turn your air conditioner completely off.

Sure, you’ll pay more for electricity than just leaving the AC off. But it’s better than paying money to repair parts of your home or paying a pro for pricy mold remediation services.

Want to catch or kill mold spores before they grow?

To prevent mold spores from getting into your air conditioner in the first place, you can either get a(n):

  • Air filter with a MERV rating of 5-6 (>learn more about MERV ratings)
  • REME whole-home air treatment system which can kill 99% of bacteria, viruses and mold found in your home