Why does my a/c keep freezing up?

The two main reasons for lines freezing are lack of refrigerant and air obstructions. It sounds like you have ruled out clogged filters. Can you get under your air handler to look at the "wet" side of the evaporator coil? If it is clogged with mold and/or debris it will cause your unit to freeze. Likewise, rule out a collapsed or obstructed return or supply duct. If you are getting lots of air flow out of your ducts, but it just isn't cool air, it's safe to say that you are low on refrigerant and it's time for a service call. Hopefully, it is a very slow leak and a simple recharging will get you through the summer. Good luck!

My window unit just did the same thing and the repairman told me that the line that supplies the freon was partially stopped up and not getting the freon to the coils. My unit would shut down completely. He told me it would cost about $200 just to take the line out, put a new one in, and replace the freon. That may be your problem. If so, you need to call a repairman. I just decided to buy a new and bigger unit. You might try raising the thermostat so it does not have to work as hard, or even turning the whole unit off for a few minutes to let it deice and cool down. I am not a repairperson, but that is what I was told.

Check the A coils (the cold coils inside the air handler that are frosting up) for blockage of dirt and grime. I did not see anyone mention the condenser coils being blocked with dirt, dust or grass clippings or leaves as this being blocked could very well be the problem also make sure that the condenser fan is turning properly. If you cannot find anything wrong with these or the air flow through the system then it may be low in refrigerant.

You said it all. Its 100 degrees. If your system is not up to par, it cannot do the job when it gets really hot outside. Your system was probably not designed with consideration being given to an outside temperature much above 90.

If it has been working until now then there are for the most part only three things that can cause your problem.

#1 - LACK OF AIRFLOW

#2 - LOSS OF REFRIGERANT

#3 - OBSTRUCTION INTERNAL TO THE REFRIGERANT LINES.

I hate to tell you, but you probably need to pay the $100, and get some help.

In short, you may have to pay for that service call. Sounds like you light be a little low of coolant (freon). Not something you want to mess with yourself unless you have the equipment and experience.

A service call shouldn't be that much, Maybe $50 -$75 depending on where you live. But at 100 degrees, won't it be worth it?

You probably have it turned down too low. It should be set for no more than 15 - 20 degrees cooler than outside.

Also, you should have one or two windows cracked. That is the biggest cause of A/.Cs freezing up.

You need to check under the filter (unfortunately, on hands & knees)

to make sure the airway isn't clogged or dirty. Especially if you have

pets. Defrost the unit, climb under with a flashlight & check.

make sure your filters are clean, the return air vents are not blocked. If these are all ok you have a leak and need it repaired and your unit recharged up.

the humidity is too high, set the thermostat higher so it has a chance to thaw

You need to have freon added. A professional must do this.