The other day, we found some water on the floor in our utility room. After some research and investigation, we discovered that the drain pipe from the central air unit was blocked. We were able to use a vacuum to unplug the drain line, and since then it has drained normally.

However in the meantime, we had some water on the floor, some in the blower compartment of the AC unit, and a lot of standing water in the condensation pan in the unit. We have had some bad experiences with water damage and mold in the past so I wanted to ask:

  • Do we need to be concerned about the water that leaked from the catch pan into the blower compartment?
  • Should we try to wash out/bleach the pan or anything? (It is very hard to get to!)
  • Should we have an HVAC tech come look at the unit/blower to check for damage?
  • Should we do anything special to prevent mold growth?
  • Is it worth it to have our ducts cleaned?
  • 1
    To prevent future blockages, try adding some bleach in the drain line periodically: diy.stackexchange.com/questions/1717/…
    – BMitch
    Jul 15, 2011 at 12:10
  • @BMitch Thanks for the idea and link; I searched DIY for leak/drain-related questions but missed that one! Jul 15, 2011 at 14:09
  • I've heard suggestions to use some diluted bathroom cleaner to prevent mold/mildew within the AC unit, but I'm curious of others thoughts before actually suggesting this option. Particularly since you can't easily wash it away and I don't know if any of these would be corrosive.
    – BMitch
    Jul 15, 2011 at 14:30
  • I've heard that a cup of bleach into the drain pan every 6 months is the thing to use; the most common cause of blockage is mold/algae, and bleach works very well without being corrosive.
    – KeithS
    Jul 15, 2011 at 15:06
  • 1
    No more or less dangerous than having your washing machine giving off bleach vapor in its steam when you run a load of whites, or mopping your floor with bleach. It might be disagreeable for a few hours, but nothing serious. The fact that the pan is not heated, and the bleach should be draining out the overflow, shoudl reduce any unpleasant side-effects considerably.
    – KeithS
    Jul 15, 2011 at 18:47

2 Answers 2


What else got wet besides the pan? Did the pan drain to the outside properly?

IF you got drywall or insulation water-logged, you will want to thoroughly dry those areas. It's not really worth it to clean out your ducts unless there is a lot of debris in them... The debris is what would mold, and with the constant movement of dry air over it, it's unlikely to stay moist enough long enough. Other than that, I don't think there is any necessary work to do besides making sure it doesn't happen again!

  • There was some water on the tile floor, but mostly I was worried about the standing water in the condensation pan (backed up while the pan drain was plugged). Two months later, it seems to be okay after doing basic cleanup and drying. Sep 27, 2011 at 14:54
  • Sounds like the pan did it's job. Just to be clear -- was that the integral drain for the coils, or was it the emergency pan below? Don't forget to test the emergency drain once a year by pouring a bucket of water into it. I found last year that mud daubers or something had chosen to lay eggs in the outlet for my emergency pan. Sep 27, 2011 at 15:26
  • As far as I saw there's only one pan, that the condenser sits in, inside a large cooling chamber that leads to the house's ductwork. The pan drains via pipe to the utility room floor drain. Thus my concern was rust/mold from standing water in that pan. Sep 27, 2011 at 19:21
  • Ok, it's unlikely to get rust/mold in that pan. There should be another pan that the entire HVAC unit sits in or over, and this qualifies as the 'emergency' pan. It needs to drain directly to the outside. This is to make sure that water doesn't end up in your house when the integral, interior pan fills up... Sep 27, 2011 at 19:29

Wet/dry vac to clean up the standing water and a few fans blowing over the wet area until it is fully dry.

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