Asked on Dec 5, 2011

A/C smells.

Jay TaylorAce Solves It AllWoodbridge Environmental


I had a new HVAC system installed 3 years ago. Going back between heat and AC this time of year. When I turn on the AC, it get this 'Dirty Sock" smell. I've used the spray "Dirty Sox", as the HVAC people use. It works. Just wondering if there was a more permanant solution? It's a new system, should not do this. It's a heat pump, Trane Seer 16 (Lxi I think). We replaced everything both outside and inside, except the duct work.
5 answers
  • The smell your getting is from the dirty water and dust collection on the coils of the AC system when it drys out when the heat turns on. You need to check your filter system for by passes and proper cleaning. If you use a throw away filter its not trapping enough dust to help prevent this from happening. What your smelling is mold development. Its important that the condensate drain system as well as the coil inside the plenum that sits on top of the furnace, nor next to it in some cases. Is pitched properly and is draining not leaving any standing water in it once the AC turns off. As far as the duct work being at fault. The return side can be an issue if its leaking air that could be bypassing the filter system. Many homes have filters placed on walls or ceilings and quite often have many leaks that allow air to enter after the filter system itself. When this occurs the dusty air gets onto the damp wet coil when the AC is running then sticks to the fins. Once heat turns on this burns off and creates the odor. The smell will not really hurt you, unless you have mold allergies or are sensitive to smells. But its a sign that your filter is not working quite as well as it should.

  • Clay B
    on Dec 8, 2011

    I'm surprised to hear the filter may not be working as well as it should; when system was installed, we got Trane Clean-Air Effects system on both upstairs and downstairs. I will have to check the draining pan under coils. I see water coming out outside, but maybe it's not fully draining, if it's not, I will call back the installers. If not that, maybe we should replace the return ducting. The installers 'supposadly' checked and retaped any ductwork during the install. I do not smell anything when the heat is on, just when I run the AC after it's been off a while (days/week). Based on what you said, and what I know, I'm betting on the drain pan has standing water, I'll repost once I check it.

  • The filter can be bypassed if its located in the living area and ducted down or up to a furnace/AC system. Quite often panning is used to create ducts out of the framing system within the wall. If this is the case your getting dust from leaks in this cavity. You can check for sure if your having a dust issue that may be collecting on the coil by simply opening up the fan compartment on the bottom of the furnace after turning off the safety switch. Then carefully reach around into the blower itself. You will be able to feel the cupped shaped fins of the blower wheel. Now carefully rub your finger inside one of these cup shaped fan blades and then check your finger for dust. If you are getting any on your finger the filter is not doing its job, Be careful when doing this as sometimes the edges of the fan blades can be a bit sharp.

  • Ace Solves It All
    on Dec 9, 2011

    hi Clay, contact the contractor who installed it Trane and others have had this problem once in a while. the solution most of the time is remove the coil and install a new one and it should be covered under warranty. good luck charlie

  • Jay Taylor
    on Jan 17, 2015

    There may be a number of reasons that lead to a weird smell coming out of your air conditioner. There may be fungus growth in or around the unit or it may be possible that there is some drainage issue and moisture is retained in the unit. For more information you can visit the link: . Hope you get your answer there.

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