my home ac unit keeps freezing up

You can't put a 5ton evaporator in a 3ton air handler. As it's been point out your fan alone doesn't have enough CFM for a 5ton evaporator.

Even if you speed up the fan then you will have too much static pressure in the air handler thus create another problem of very turbulant noisey air flow.

Did the installer size the new split system refrigerant lines for the 5ton unit or use the old 3ton lines that are too small?

When you change the condensing unit, most mfg's you now have to change the evaporator coil at the same time as there a matched set, but that still doesn't resolve your problem of too small of air plenum.

Without knowing more info it sounds like you got ripped big time by the installer. If this in fact is true, then he doesn't have enough knowledge to install a completed working sytem so I would get my money back and tell him to come get his equipment, then call a qualified contractor.

T_Bone

I think that the others are right in saying your old unit does not move enough air to keep the new unit satisfied.

I also feel that when you get it fixed you may be unhappy but for other reasons.

A trick of the trade is to sell a A/C unit to big for the house.

Yes sir it cost more and I will make me a bigger profit but you will save in the long run in reduced run time and lower electrical bills.

The problem with this statement is a A/C is designed to run for long times. It uses this time to run large amounts of air over the coils and remove humidity from the air. With a system that is to large it cools the house before large amounts of air are moved and you have high humidity problems.

I can tell you though..... .....
If your A/C contractor did not do this test and guessed at what size A/C you need based only on your square footage you most likely were taken.

Mark

If the heat load (hot house air) cannot add heat to the air across the coil as fast as the refrigerant is removing it, the ref temp will go below freezing and the condensate (moisture in the air condensing on the cold surfaces of the coil) will also freeze. The more it freezes, the more the air flow is restricted and the less your ability to absorb heat into the fluid and the process snowballs eventually to a solid iced over coil.

You 5 tons is rated at almost twice the air requirement (tons per hour) of your 3 ton. Dunno how you are going to move that much air thru the existing part of your 3 ton system.

You'd have to blow the drapes off the wall to get it right and you don't want that either.

High air velocity is noisy and you aren't supposed to hear your environmental control system; just feel it.

I guess you weren't happy with the cooling of your old unit is why you went with a bigger unit.

My thoughts are to get a 3 ton back in and increase your insulation. The attic is a perfect place to start. Then check for air leaks and stop them, and then, if you have kids, get them to KEEP THE DOORS SHUT.

Good luck.

Mark