Any suggestions about using EF22A to top off a R22 system?

Why do you want to add refrigerant to a stressed system? Don't screw with it. You have a dirty coil or not enough airflow. Change the filter, clean the A-frame. It's not refrigerant. Closed systems don't lose refrigerant. If you are hell bent and whiskey bound to add refrigerent, yeah, EF22A is a compressible gas/liquid. It's not a refrigerent problem, but do whatever.

In 15 years how many yearly service/pre-season tune ups/cleanings has the system had? If it hasn't had one in a couple of years, then its definitely time for one. You said something about having a manifold set.

Put the gages on it and see if its low, instead of just thinking the icing is just evidence its low.

Check the airflow. Change the filter, clean the evaporator, clean the condenser also. Make sure all the vent grilles are open. If it has dampers in the attic, make damn sure they're open.

IF YOU DO HAVE A LEAK,... it MUST be fixed.

I figure the jury is still out on the EF22A, and the M99 crap....but if you are bound & determined....

I have no experience with AC other then cleaning the system twice a year.

Yes, low freon can cause the system to freeze up, it is not just a dirty filter or clogged parts that can cause this issue. I have talked to multiple A/C companies and they all say this is true if you have ruled out everything else above.

I am looking for more information on the same replacement and will post it if I find it.

If you are starting to freeze up and you done clean up. You have a leak. Get some dye in system . Get someone out to check compress head pressure and look for leak. I would vac system and put in ef22a or you could just add some . Ef22a 1lb replace about 2.25 pounds of r22

http://www.refsols.com/files/Replacement_of_R22_by...

you can read this, if I was doing it I would remove all r22 and add new refrigerant , but if not experienced you may be getting in over your head. Your system is really at the end of its life but if you want to nurse it along you can do this. Just check coil, you can clean it in place with care, check blower motor and make sure you have proper air flow. You will need reclamer and EPA licence to do it.

R22 30lb