Low refrigerant or a restrictive or dirty filter are the primary causes of a coil freezing. If you are convinced those are not the problem, then check to see if the condensate drainage is working properly. If the condensate is accumulating at the coil it will eventually freeze.

Has any tech tried increasing the blower speed? You said it is work but the speed setting may be too low.

A 2 ton AC is very over sized for a 650 sq. foot apartment. If is working properly it should cycle on and off frequently but the coil should not freeze.

Is there a warranty from the original installer? If so what is his plan to correct this problem?

Maybe the installer reduced the blower speed an in effort to compensate for the oversizing.

New equipment falls to the installer who installed it.

If they can't fix it they need to take it out, give your money back.

This is why it's so important who you choose to install your HVAC equipment.

Any HVAC company worth a grain of salt isn't going to touch this machine. I know that's not what you want to hear, but because only the installer knows what they've done... no one is going to stick their neck out.

There is no warranty for improper installation. Not even the manufacturer is likely to get involved in this.

Hopefully the installer will do the right thing.

It's WAAAAAAAY oversized. That will result in very poor cooling and dehumidification. Shouldn't necessarily freeze the coil but you need to get the original installer back to fix things (they can run a 1.5ton condenser with the existing 2 ton air handler/coil).

"Maybe the installer reduced the blower speed an in effort to compensate for the oversizing."

This, too.

The old unit was 1 1/2 ton and the new one is a 2 ton.

Who made the decision to increase the size? I think the blower speed theory has merit. Perhaps the tenant complained the setting on the original blower speed was too noisy because the duct work is undersized, and someone lowered the speed to reduce the noise. A competent tech should be able to figure this out.

Mike_home said "A competent tech should be able to figure this out." and I agree. If the installer refuse's to fix it you should sue him for lost rental income. Are you telling us the complete story? Let me guess,you hired some fly by night that has no bond,no money or insurance because he was the cheapest you could find. Explain this if you can. If all the bozos that tried couldn't fix it,what make's you believe strangers a thousand miles away can without ever seeing it?

The single most common reason why your AC can freeze up is lack of airflow. This can be caused by a number of different malfunctions ranging from the blower motor to the air intake. If anything in the airflow system stops warm air from flowing over the coils while the compressor continues running, your AC will start to freeze up and this only gets worse with time.