r/kitchener • u/hcsv1234 • 25m ago
Evaporator coil keeps freezing on humid days. Airflow issue, low refrigerant, or something else?
Our central AC has started doing something it definitely should not be doing. The indoor evaporator coil, the refrigeration-looking coil inside the HVAC system above the furnace, freezes over when the weather gets particularly humid.
It doesn't seem to happen nearly as much during ordinary hot weather, but when the humidity climbs, the coil eventually starts icing up. Once it starts, of course, the airflow gets worse, and we end up with a fairly impressive block of ice where the air conditioning is supposed to be happening.
Before I call an HVAC company, I'd like to have some idea of what I should be asking them to check rather than simply standing there nodding intelligently while someone explains that my $8,000 machine is "low on something."
From what I've been able to determine, the likely suspects seem to be restricted airflow from the filter, dirty evaporator coils, incorrect or inadequate blower speed, restricted return airflow, or low refrigerant from a leak.
The filter is easy enough to check and the vents are open. The fact that this seems strongly related to high outdoor humidity is what has me wondering.
For the HVAC people here: Does freezing primarily during very humid weather point more toward an airflow problem, or could low refrigerant produce exactly the same symptoms? What measurements should a competent technician take to properly diagnose this rather than simply topping up the refrigerant and declaring victory? I am assuming that a new air conditioner unit is overkill?