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Question DetailsAsked on 9/12/2016

Is it normal for the drain of a new AC unit to be constantly clogged?

The unit is currently 10 months old and already had three instances of clogged drain. The technician is from the same business that sold and installed the unit and says that clogging is common with humidity and during hot months - it clogged in June, July, and now in September. Every time he comes over I am charged $168. I was wondering if there could be another underlining problem that I am not being informed of, such as installation or faulty unit, or if this is a common issue. I live in South Florida and did not have this problem with my previous unit. Thank you!

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1 Answer


Common, like he said especially in humid warm climates - but should not be occurring that often - should make it from annual unit servicing to next service without clogging up.

Condensate colection pan should drain toward the drain tubing, so it does not pool in the pan and form sludge and grow a fungal farm which blocks the inlet of the drain.

Drain line should also go as direct downward to the drain (or condensate pump if needed) so the water drains out rapidly without stagnating in the tubing.

There are some types of drain tubing that crud up quicker than others - generally speaking, the "softer" the drain line material, the quicker it cruds up. If it is plugging up in the tubing rather than at the pan, there is also condensate tubing impregnated with fungicide to reduce this. Also, larger diameter tubing will clog off slower.

There are condensate pan fungicide tablets which kill off the algae and fungal/mold growth - be sure it says it is safe for the metal you have in your pan (some corrode copper or aluminum pans). Calgon is one brand name which has made these for scores of years - called Pan Treat or something close to that. These type tablets are available at box home improvement stores, plumbing supply places, Amazon, etc. Have to be placed in a location where the condensate wets them, and last from a month or two to up to 6 months depending on amount of condensate your unit generates (and in your locale, more condensate quantity means your unit is effectively dehumidifying your home, so that is not a bad thing). Does require (depending on installation may mean a gasketed access hatch has to be cut in the ducting for you to put them in the pan periodically) accessing the pan through a panel in the ducting or air handler.

There is also liquid fungicide kits that install through the ducting down to the pan, with a little permanent funnel mounted on the outside of the ducting, which you pour a measured amount of fungicide into every few weeks or month or so. Available at some home improvement stores, most plumbing and HVAC supply places.

One thing - there are also copper metal mesh or grid or loops of wire that you lay in the pan to act as a fungicide - use this only if plastic or copper or stainless condensate pan and non-metallic or copper tubing, because will cause corrosion and holing-though otherwise due to electrolytic corrosion.

While chlorine bleach will kill it off, generally bad idea to use in that application - corrosion potential in the pan and coil area, and bleach odor will permeate the house.

If you have him come again to clean it and maybe change to a larger or fungicide tubing, see how he cleans it too - if you have an access port through the ducting, not hard to wipe out the pan (being VERY careful not to ding or bend the evaporator coil elements) and run a cleaning swab or brush down the tubing (if the tubing is short). Also, normally real easy to pull the tubing off (if flexible) and take and clean it in the sink - running a swab or long small diameter brush through it on a string to clean out the inside.

One other thing on the three cleanings in 10 months - this is definitely inordinately frequent, so if you have a one year warranty from them on parts and labor I would be demanding my money back for the visits and tell them to fix the problem at no cost to you.

Answered 3 years ago by LCD

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