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  1. #1
    Join Date
    May 2007
    Posts
    35

    A-coil totally iced up

    A/C unit was running, but noticed no air was coming out of the vents. Went in the basement and found the A-coil was a solid block of frost and ice. What causes this? It ran fine all of the weekend when it was very hot out. Only difference today is that a thunderstorm passed through and it is very humid outside. The ice goes from the A-coil and entire insulated line all of the way outside and to the compresser. Could this be as simple as the A-coil needing to be cleaned? Here is a pic, hope it shows up well on this post.
    Last edited by VincentR; 06-11-2007 at 06:37 PM. Reason: made picture bigger

  2. #2
    Join Date
    Nov 2006
    Location
    New Hampsha'!!!
    Posts
    274
    check the filters, evap fan motor, check pressures...if supicious look for a leak and then check out the metering device. lack of airflow across that coil is my geuss.
    dont worry what people think, they dont do it often

  3. #3
    Join Date
    Apr 2007
    Posts
    6,285
    Low charge or low airflow or a restriction in the line. With it being really humid out the dew point if fairly high and for whatever reason the coil is below 32F and is freezing the condensate instead of it running off. You can thaw it out by letting the fan run in the on position but you should NOT turn the A/C back on until you have someone look at it.

  4. #4
    Join Date
    May 2007
    Posts
    35
    Fitler is clean (only about a month old), evap fan was running. Guess I'll have to thaw it out and call someone. Unless I see a blockage in there somewhere.

  5. #5
    Join Date
    Apr 2007
    Posts
    6,285
    Thaw it out completely. Sometimes you can find the weirdest things stuck to the coil. If it's not a blockage it could be low on refrigerant in which case you may have a leak or it just wasn't properly charged. If the pressures are low the evaporation point is low and it causes the evap coil to become below freezing temps so when the condensate flows over the 31ºF or less coil it freezes. Are you sure the evaporator motor was running the whole time and it didn't cut out or stop while the condenser was still running? Bad fan motor or bad run cap's can cause this same problem and give the perception it's low or clogged.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,357
    Quote Originally Posted by VincentR View Post
    A/C unit was running, but noticed no air was coming out of the vents. Went in the basement and found the A-coil was a solid block of frost and ice. What causes this? It ran fine all of the weekend when it was very hot out. Only difference today is that a thunderstorm passed through and it is very humid outside. The ice goes from the A-coil and entire insulated line all of the way outside and to the compresser. Could this be as simple as the A-coil needing to be cleaned? Here is a pic, hope it shows up well on this post.

    I can see the dirt through the ice.

    If it ran fine all weekend but iced up after the t-storm, chances are outdoor temps dropped off but humidity spiked, which found its way into your house and to a coil surface temp running below freezing due to reduced airflow (via dirty coil), less sensible load from house interior (that is, until coil froze over ), and lower head pressure (resulting in better net refrigerating effect due to incoming liquid column to metering device - likely a piston - being cooler).

    In non-technical terms it means if I can see dirt through the ice, that coil needs to be cleaned. Filters only trap part of the dirt and dust that pass through them.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  7. #7
    Join Date
    May 2007
    Posts
    35
    Thanks guys. I have the fan only running now. I also used a hair dryer on the coil to melt most of it. My condesate pump is getting a bit of a workout. I'll let the fan continue to run. How do you go about cleaning that coil? There are no service panels on it. The view in that pic is where I removed the "aprilaire whole-house humidfier". Yes it was turned off!. I have it unplugged and the water valve closed to it during the summer.
    As far as the evap fan running, I am almost certain it was running fine. I had an issue a few weeks ago where it was not running, but that turned out to be a bad run cap. It was bulged. I replaced tha cap and the fan motor has been running fine since.

    .....you can see dirt through the ice? Wow. I couldn't even see it with a drop light! Guess I need glasses.

  8. #8
    Join Date
    Apr 2007
    Posts
    6,285
    Quote Originally Posted by VincentR View Post
    Thanks guys. I have the fan only running now. I also used a hair dryer on the coil to melt most of it. My condesate pump is getting a bit of a workout. I'll let the fan continue to run. How do you go about cleaning that coil? There are no service panels on it. The view in that pic is where I removed the "aprilaire whole-house humidfier". Yes it was turned off!. I have it unplugged and the water valve closed to it during the summer.
    As far as the evap fan running, I am almost certain it was running fine. I had an issue a few weeks ago where it was not running, but that turned out to be a bad run cap. It was bulged. I replaced tha cap and the fan motor has been running fine since.

    .....you can see dirt through the ice? Wow. I couldn't even see it with a drop light! Guess I need glasses.

    But what caused the bad run cap?

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