If the air flow is too low then the coil could form ice. This could be caused be a restrictive filter or the blower speed it too slow. What type of filter are you using? Have you talked to the installer about the problem?

You've answered your own question. If airflow across the indoor coil is too low, insufficient heat transfer to the refrigerant will take place. Moisture in the air will condense on the coil but will freeze. Super cold refrigerant being delivered back the the condenser will cause frost on the the low pressure pipe. This can be caused by restricted airflow, too low airflow or low refrigerant. The fact that has only started happening leads me to believe its the latter.

Reduce the resistance to airflow caused by the filter (filtrete?) and/or increase the blower speed. Then get the system checked out for low refrigerant.

Why are you asking people that never saw the equipment when you just paid someone to install it? If you were given a list of a dozen things that can cause freezing lines,what is your next move? Get the yahoos that installed it to fix it.

Yeah I agree with Klem1, you need to get the yahoos that installed it back out there.

I'm curious why you didn't do that already?

The new unit was installed three days ago, so I can rule out low refrigerant. I threw out the old return air filters and replaced them with the cheapest, thinnest ones I could find. Problem solved - no more ice.

No, your problem has not been solved yet, some thing wrong with your blower, you are OK now without the filter (or with cheapest filter), but not 2 or 3 years from now when your blower getting old. You need to call the installer back to fix the blower so that you can use all kinds of filters. (check the charge too while the tech is here, just to make sure the charge is OK)

@Mark Andersen

As others have mentioned, you need the proper airflow over the coil and the proper charge, etc.

However, I strongly disagree with @Cima Locert.

Air filter companies are producing replacement filters that are stupid in what they cost AND how restrictive they are to airflow. You can't substitute super-restrictive filters unless the system was designed for them and has a much larger filter area.

Don't run your system with no filter. You don't want pet hair and lint to get on your damp coil. However, a standard (cheap) filter is just fine. If you want to use super filters, you need to re-design the filter box.

New systems are installed every day with the incorrect amount of refrigerant. It is possible the refrigerant is low on a 3 day old system.