Help! Sense helped identify when AC flakes-out & gets iced-over


I’ve had a problem for the past few summers where my AC chiller/exchanger inside my blower ices-over.
I was working outside and noticed Nest was trying to cool the house but the house temperature kept rising.
I checked Sense and the AC bubble was missing, but the Other bubble was showing 1.1Kw (half power).
I turned off the AC via the Nest app and the other bubble disappeared.
Went into home and turned on the AC, no air was coming out of the vent (blocked by frost or ice). And only the Other bubble would show up about 100W less than the AC would normally operate at (normally operates at 2200W), but steadily drop in wattage every second.
I turned off the AC. I’m glad to save energy of the stupid AC is broken, but I could’ve identified this without Sense, but it was an interesting find on how the AC drops power steadily after turning it back on.
On the side, If anyone knows where my problem lies, I’d be grateful for a solution on why my AC air handler ices-over I’ve tried new filters, different filters, cleaning my condenser fins… My AC freezes up a few times per year. Each time, we let the AC thaw-out for a couple days before running it again.


Freezing indicates one of two problems. Either there is an airflow issue, or your refrigerant charge is low.

Make sure you’re using a filter rated for the airflow you need, and have the system checked by a qualified HVAC technician.


Hey MachDrone, good use of your Sense! Now to your inside handler. Could be lots of things. A dirty filer is the first and you checked that. Is the filter of a kind that does not restrict air flow? Heat pumps are designed to run with good air flow. Are all of your registers open? When you thaw the inside air handler is it dirty? You can thaw it with a hair dryer and not wait all day. If it is dirty, a can of coil cleaner will help this and a cheap fix. If it is clean and you have good air flow everywhere then most likely you are low on freon. A freon leak can be difficult to locate. If it is a big leak you will see a greasy spot. This is best done by a qualified technician. There are leak detectors available but most servicemen just add freon. Sometimes they add stop leak too. How old is the unit?


I jumped the gun on calling-out the iced-over. I’ve had that case many times… Imma needing a professional. lol
I have tried many types of filters off the shelf, but didn’t think of cleaning the chiller exchanger… I don’t know what filter CFM is required by my unit.
I don’t know the age since it was installed by previous owner, but will look up model number on Google to see the era… I know it’s over 10yrs old.
Registers are open.
The work-around I have, which I may continue for remainder of this summer, is to run AC for an hour and have only the fan run for an hour.
This has been keeping the AC reliable and keeping house at the temp I aimed for.
Something else that may be making my work-around successful is that I’ve been shading the long South wall of my house since 4th of July.


Icing is also a problem with oversized A/C units. This is really common in the U.S. Techs are too lazy to correctly size the A/C unit according to the needs of the house. The is a formula in manual J (google A/C sizing manual J )for getting this correct. It can also be an issue for a house that had the correct size but was then well insulated. Then the unit can be too large, especially if the house had little or no insulation in the past.

Another problem is that the return line is too small for the A/V unit. Not enough air is passed over the coils so they get too cold and freeze the humidity in the air. The A/C owners manual should have information regarding the minimum duct inlet and outlet sizing.

If the air comes out really cold, then it could be that the system is too large for the house. I think there are also valves that can help with this. They are called TXV and are default in later systems. Here is some info on them

I use the Nest thermostat. It has a system called “Airwave”. All it does is run the fan for a few minutes after the compressor has been turned off. It can help a little with iced over units, however, the root cause of the problem should really be addressed.


It could be ANY of these problems mentioned by each of you… Are there any of these problems that could be hurting the life of my equipment? I’d want to start there first or act quicker with an expert…


I was told by an AC installer when I lived in Colorado to keep the fan blowing, even when the AC isn’t running. There’s just enough humidity to ice the coils, and keeping the fan going helps prevent it - it’s even more common in more humid environments.

I’m sure the other ideas are valid, too.