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Where I live, it’s already pushing 90 in the heat of the day, so a/c is your first, last, and only line of defense against sweating your ass off.  Unfortunately, this frosty image means that my a/c unit wasn’t cooling much of anything, despite the ice on the outside of the coil.  In this case, ice is not cool.

There are tons of reasons an evaporator coil will freeze over like this — one of the most common is restricted airflow across the coil.  This allows the temperature of the coil to drop below 32 degrees, causing the humidity/condensation to ice over.  It’s also why the repairman will ask you how long it’s been since you changed the filter, since a clogged filter is often one of the root causes.

If this happens to you, shut off your system immediately.  Running it while the return can’t get enough air to the system will damage the compressor if you leave it for too long.

Lucky for me, it turns out the filter in the return was too restrictive, and as soon as the unit thawed and a slightly less restrictive filter was popped in, all was right with the world.

Note: Keep in mind that if you’re not sure about what to do with your a/c unit — never guess.  Just call a pro.

Furnace Filter Tips [Healthy House Institute]


7 Responses to Ice Isn’t Always Cool

  1. FredB says:

    Call a pro? What fun is that?

  2. My parent’s professionally installed AC/Furnace system didn’t have enough return airspace to ever properly move air across the evaporator and it would freeze over all the time. My dad ended up building additional ducts into the walls so that they could have a functional central air system that doesn’t need to be tended to constantly to prevent freeze up.

  3. george says:

    most times this is an indication that the evap sensor is not working properly. the comp should be cycling on and off to prevent this.

  4. Brice says:

    Most home ac units don’t have an evap sensor. They are most commonly used on zoned system. They are cheap but can often mask a more serious problem and should not be added until all possible problems have been checked.

  5. SunnyDHVAC says:

    most of the time a frosted ac coil will me a airflow or pipe obstruction and or low refrigerant causing the liquid to flash into a gas to early. clean your return air coil and change your filter. if you come across a frosted coil such as this turn off a/c and set t sat to fan on to defrost coil, clean your coil change filter, then when all the simple stuff is down check the outside coil for leaves sand etc clearance then you put on the gauges.

  6. arby says:

    When checking out your A/C, don’t forget to check the drain hose from the catch pan. If it is obstructed, then the water will sit higher in the panand start to rust out anything it contacts.

    The “professionals” that installed my system forgot to program up most of the energy saving functions. Good thing they left the manuals so I could finish their job. 🙁

  7. kyle says:

    half the time pros only do half the job do it yourself and lear somrthing new

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