When we got home from vacation, our upstairs A/C was on, but no air coming out the registers...
I thought "The A coil is frozen" and shut the unit down for 24 hours...
Fired it back up, and all is well. Until the next morning. "POOP, frozen again" and shut it down.

This time I thought maybe the air filter was clogged, so I removed it. Nope, this morning itsa solid block of ice. I've had this happen before but it was always an isolated incident and back to normal after thawing it out.

Why would this keep happening?

Usually means unit is low, time for service

I'd be willing to bet it's a low charge.

If you attach your A/C manifold and read the low side for R22, there is a corresponding temperature scale per pressure indicated. This temp scale tells the temp of the evap coil.

Other suggestions would be the cleanliness of A-coil and fan blades, and ductwork on the discharge side.

Website:

www.chillercity.com/Refrigerants/Press_Temp/hspc.pdf

Hi Jim, coil freezing is usually due to not enough air across the coil. Like you said, ck the filter first. Also, are all your registers open? Sometimes when it cools down at nite and your ac is running the refrigerant returning to the evap. coil can be "too cold" Your system may not have frozen up before but may have been on the "edge" of it, The fan speed may have to be bumped up one. Make sure none of your flex ducts have been colapsed.
Let me know, Gary 315-730-9420

Yup, blocked coil air flow (not enough vents open too), blocked filter or low on refrigerant. Had this same problem recently and had both dirty A-coil and low on R-22

If it is a system several years old, the coil gets gunked up-no matter how often you change the filter. No air flow then freezes.

If it is all clogged, you will have to clean it out, blow it out, vaccuum.

Thanks guys. This is "the little system" for the upstairs, about 10 years old, troublefree until now. It was frozen when we got back from vacation, and has frozen twice more this week.

I pulled the filter yesterday and it froze again anyway. Filter is an air bear, 6" thick pleated, it looks like new. Ducts are fine, and she flows plenty of air when not frozen into a solid block of ice.

I let her thaw today and cleaned the outside coil, which was disgusting btw, if it freezes tonight, I guess I'll have to "call the man"

I would say it is low on refrigerate / freon.

If it is low on refrigerant you probably have a leak,if it is an r-22 system you should consider a new system,r-410,and take advantage of the energy tax credit.r-22 is going away,price going up like r-12 did.I deal with these situations everyday,you can pm me if you have any questions.

blocked condensate line will cause freeze up

Seems like it's the evap coil is dirty...usually is the cluprit...or low charge...a quick hook up of the gauges might tell the story...

blocked condensate line will cause freeze up

Um,...no

Jim, is the Evap motor belt driven? If yes and you have not changed the belt out in the 10 years you have had the system then it could be the culprit. Not enaough CFM blowing across the coil could freeze it up. Another lead would be the motor could be going out on an internal overload switch. You mention the blower works well. But sometimes those internal overload switches shut the motor down and then reset themselves. They will shutdown long enough that the coil would freeze over.

Did you call "the man"?

Did you call "the man"?

Andy to Aunt Bee, right??