Ice on Outside unit
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  1. #1
    Join Date
    Feb 2007

    Confused Ice on Outside unit

    Sorry if I am not using professional terms. I am just starting to learn about HVAC, by learning about my home unit first. The unit outside of my home has ice on it. I have 2 friends who have received their license but giving me different answers. 1 said that it is due to low freon. There might be a leak somewhere. So, I told my cousin to come and fill the freon, but he said that freon cannot be measured when the temperature is cold outside. I live in Charleston, SC and the weather is around 50-65 degress. Is that true? Please help!!

  2. #2
    Join Date
    Aug 2004
    Kentucky, Michigan, Ohio, Arizona, Colorado, Nevada, and Califormia

    Red face

    More info. Is it a heat pump or straight ac ? If straight ac... yes that could be true. Most charging charts do not allow for low ambient operation (barring commercial, or systems equipped with low ambient controls). If it's a heat pump there are more likely causes for freeze up. You didn't mention how long they have had licenses. I'd call an established company for service. For too many years the solution to everything was "add freon". This is the last thing that should be done. If it is indeed low, you have a leak or it was never charged properly to begin with. Adding "freon" without knowing the root cause of your problem will lead to much bigger problems.
    "Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
    Clark Griswold

  3. #3
    Join Date
    Apr 2005
    NE PA
    Icing on outside coils of a heat pump is a common, normal condition. Assuming that your filter and outside coil is clean, icing usually is part of the normal operation. When the outside humidity is up, and the temperature of the outside coil is below the dew point, frost and ice will form on the coils. It is more common in weather that is not too cold, and humidity is high (damp weather).

    This ice is controlled by the heat pump defrosting, which reverses the cycle to use house heat to melt the ice, while supplemental heat keeps the house warm. On lower cost units, defrost is a function of run time and coil temperature (called time-temp defrost). Higher end models use demand defrost which measures several temperatures and determines if the coils have lost capacity to pick up outside heat.

    In either case, if the ice is not that significant, it is normal. If it continues to build, it will eventually defrost and clear the coil. If the ice builds up to completely cover the coil, there is likely an issue with the defrost controller or sensor and may need a service technician.


  4. #4
    Join Date
    Feb 2007

    Ice on outside unit

    Thank you for your info. Is it true that freon level cannot be measure when the temperature is cold outside?

  5. #5
    Join Date
    Mar 2001
    No it is NOT true. Inside there should be a charging chart, subcooling and superheat readings can be used as well as weighing in the charge. Call a licensed established company before your friends or family damage your system.

  6. #6
    Join Date
    Nov 2004
    SW FL


    Quote Originally Posted by agt View Post
    Thank you for your info. Is it true that freon level cannot be measure when the temperature is cold outside?
    Heat Pump or A/C unit.

    Cold is relative, you mean < 32'F?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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