Why is My HVAC Leaking?

As summer blazes along in the Phoenix area, one of the things that can badly affect an HVAC system is dirt and algae in the drain line. The problem can manifest itself in the form of a leak from the drain pan at the drain pump. A leaking HVAC system inside the home can cause water damage, and even mold, before the homeowner realizes what is happening.

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The refrigerant coils in the air handler unit contain freon, which cools the blowing air from the intake vent. Intake vent filters are designed to keep dirt and debris out of the system; however, if the filter isn’t installed correctly, is allowed to get very dirty or is poor-fitting, this will allow debris to get into the system. This dirt can adhere to the coils, which develop condensation from the freon.

The water from the condensation can be dirty as a result. The dirty water then travels through a condensate drain line, which is pumped out of the house. But, the system doesn’t pump the water at a steady pace. If the water in the drain pan or in the lines has time to sit, it can grow algae. 


Algae and debris can cause problems for an HVAC pump and lines. The pump line and drain lines can become clogged with algae, which results in an overflow of water into the home. There are several ways to deal with this.

If the condensation line doesn’t have a cleanout pipe, the condensation drain pipe has to be cut, and the line cleaned out with a wet/dry vac if the clog is in the air handler, itself, in the primary drain line. The system may require several cleanings before the lines run clear. 

If there is a cleanout pipe, oftentimes the homeowner can open it and pour a little bleach or vinegar in the line so algae and mold doesn’t have the opportunity to grow. The line from the air handler to outside the house still needs to be cleaned out, preferably with a wet/dry vac.

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If the homeowner gets a Spring a/c checkup, the technician can find the problem and clear it up before it ever becomes a leak. This isn’t always the case, though, because these types of clogs are tricky in the same way plumbing problems are tricky: the drain works until it doesn’t. In some cases, the leak may be small enough that it traps moisture and causes mold before the homeowner realizes there is a leak. 

Because of this, a wise homeowner will take a moment to check the drain pan and pump area once a month when they change their air intake filter. If a homeowner detects a musty odor near the air handler, it may well be that it has started to leak and mold and should be checked out.

 If the condensate pump fails, this will also result in the condensation water leaking in the home. We will talk about the condensate pump more in our next blog.


911 Heating, Cooling, and Plumbing can service all commercial and residential HVAC and plumbing needs. Call 602-795-2900 today!