A/C unit freezes - no tech can figure it out - HELP!

So here’s the nightmare story of a broken A/C unit, what’s wrong with it, and the story as condensed as I can make it…brace yourselves…

3 years ago my A/C broke and we had the condenser replaced. It was very old. The work was performed by a contractor provided to me by my home warranty company. A year later it stopped working, the warranty company sent someone else, and they replaced the coil inside the furnace to make it compatible with the new outdoor unit, something that should have been done originally.

Fast-forward two years. The lines are covered in ice, the coil inside the furnace is a block of ice, and there’s ice all over the lines and middle of the condenser outside. The first tech comes out and says it’s because of poor airflow. He replaces the furnace (also about 25 years old). The A/C runs for a few days, then freezes up again. He comes back and thinks it’s a defective coil. He replaces the coil inside the furnace (even though it’s only about 2 years old). It runs again for 3 days, then the same thing…ice everywhere.

A new tech from a different company comes out next. He says it’s low on Puron refrigerant and a coil outside also has a small leak. He’ll be back soon to replace this coil and add the refrigerant. I asked him if this is what’s causing the unit to ice up, as that’s been the recurring issue over and over again, and I got a bit of a wishy-washy response of, “Well it might be what’s causing that.”

I’m worried he’ll come out, do this small fix, then everything ices up again. Any suggestions on what else could be causing this?

Do you remember what the capacity was of your old compressor versus your new one? Like if you went from a 2 ton to 4 ton or something? If the new one has much more cooling capacity, it could be that there’s not enough heat in your house to take all the cold from the AC lines. It’s not immediately obvious, but the capacity of your condenser needs to be balanced against the size of your house. A too small one will never be able to cool off the house, and a too large one won’t be able absorb enough heat from the house to warm up the freon.

If you don’t remember the capacity of the old one, look around your neighborhood and see if anyone still has the original. If your neighborhood was built by a single developer, it’s likely they used the same AC on many houses. You might find someone who still has the original.

Low ‘freon’ would cause freezeups, and would be one of the first things to check. Also this is from car a/c’s IDK about central a/c in this respect, but there is a orifice which over the years can get clogged, this also causes freezeups and can appear like low freon if you only check the ‘low’ side. The high side would read higher.

We’ve had window units freeze solid inside when they somehow have refrigerant escapes and the overall refrigerant volume drops past a certain amount. About all you can do with window units is get a new one. A new central is a little more expensive.

In an older trailer, I kept the fan running all the time to prevent the coils from icing up.

The commonest causes of freeze-ups are:
[li]low level of refrigerant gas (leak or slow diffusion)[/li][li]insufficient air flow (dirty filter or other blockage in the ductwork leading to the evaporator unit, or evaporator coils dirty due to improper filter or insufficient filter changes)[/li][/ul]
It is also possible that a mismatched condenser/evaporator could be the problem, but I don’t think it would have taken 2 years to show up.

Is it possible the blower in the furnace stops working intermittently? My furnace has glitch where, if the power goes out for a second or two, or if I turn it off and then back on, sometimes the condenser fan turns on but the furnace blower doesn’t. And if I don’t notice soon, it will freeze the coils on both ends. Then I have to turn it off for several hours to let it thaw back out, and turn it on again, making sure the blower comes on when I do.