Just noticed this leak stain around my AC vent - HELP!

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Background: Last year we bought this condo, we are first time home owners. The condo is on the middle level of a 3 floor garden style condo building (we have neighbors both upstairs and downstairs). It has been raining very heavily on and off in our area for last around a month so moisture level is pretty high here,
The problem: This evening after returning home from work, we noticed this stain(picture) on ceiling around the AC vent. We don't use this area of the house that frequently so I can't say for sure when this stain first came to be. Also we have hardly used AC in last couple of months since this spring and summer so far have been cooler in our area (but of course the HVAC worked overtime during winter for heating).
My preliminary internet research tells me that, there is something wrong with my HVAC system around that vent. Can anyone take a guess from the attached picture and help me call right contractor to look at this more closely?
just noticed this leak stain around my ac vent help, diy renovations projects, heating cooling, home maintenance repairs
  8 answers
  • Gregory Ervin Gregory Ervin on Jun 07, 2014
    That's probably a condensation leak from water building up around the A/C ducting. Where is your blower/evaporator unit? Once you determine the source of the leak and get it stopped, you can you KILLZ to prime the area and the leak will not show through the new paint.
  • Jeanette S Jeanette S on Jun 08, 2014
    Re-enforcing tip: When you paint this, make sure you paint this lower secton all the way from wall to wall so it won't look patched. Also KILZ any part of ceiling you want to paint because if you do not, the spot will bleed back through your paint! NEVER paint a thing on a ceiling without KILZ! Good luck
  • This is often a sign that the ducts behind or above the ceiling are not properly insulated and have proper vapor barrier installed. Ducts located in hot areas that are exposed to attics will condense water on their surface. Much like a glass of ice water on your table will get wet on the outside. This happens a lot with poorly installed and insulated ducts. The result is often water leaks and stains that surround the air discharge.. Another cause can be a plugged condensate drain. These drains that are built into the ac unit often plug due to poor service on filters as dust begins to collect and becomes flushed into the drain pipe where they cause backups on the condensate drain. All overhead AC systems should have an emergency overflow pan installed just for that reason. Any water that leaks out of the system would first collect in the emergency drain where it goes outside where you will see the water draining. lastly a low refrigerant charge will cause these stains. It happens because the inside coil ices up when refrigerant leaks out and the coil before it gets warmer, it gets really cold freezing the water that normally drains our of the pipe system. The leak happens when the system turns off and the ice melts faster then the drain can take the water away.
  • Jay Taylor Jay Taylor on Jan 17, 2015
    I think the HVAC system needs maintenance though there may be other reasons as well. You should consult a AC service. If you want to fix it yourself then you can get a little help from my blog as well, the link to it is: http://blog.specialtyairinc.com/troubleshoot-window-ac/ Hope you find it useful.
  • Rald Smith Rald Smith on Jul 14, 2015
    This is what I am seeing where the duct work runs in my garage which I have turn into a walk in closet
  • Rald Smith Rald Smith on Jul 14, 2015
    This is what I am seeing where the duct work runs in my garage which I have turn into a walk in closet
  • Deanna Nassar Deanna Nassar on Jul 17, 2016
    When was the system last cleaned? If the fins get clogged with dust it can ice up and then leak when it thaws. When re-painting the area I agree with Jeanette, use Kilz over the stained area and slightly beyond, allow to dry and repaint the whole ceiling.
  • Deanna Nassar Deanna Nassar on Jul 17, 2016
    Ps. There could be a leak from upstairs. Our apt had a similar spot on the ceiling from a stopped up drain upstairs.
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