Carrier Heating and Cooling Poor AC Quality and Service farmington, Connecticut

I own a 6yr Carrier 48KBTU unit and live in a Southern state. I am surprised that your 3 year old unit in Ohio had to be serviced twice a year to retain the 5yr parts warrantee. What nonsense! I have never serviced any of my HVAC heat pumps in either of my two homes and the worst a Ruud, Amana (18 years, the best of the bunch) and a Rheem both lasted 12 years with only two minor repairs (a starting capacitor or such) each failure in 3 to 4 year intervals. Never an in between failure of less than 2 years. Cleaning the outside conderser coil only helps to maintain its efficiency and does not prevent inside coil failures.

My Carrier heat pump runs fine for one or two years then when the evaporator/inside-coil gets a whole from the corrosion caused by aluminum fins touching the copper tubing it starts to cool poorly (7 degrees of temp difference between intake to first register, while 16 degs diff is normal when fully charged). Summer heats result in higher internal coil pressures and the weakest spot just fails, leaking R-410A.

There is an evaporator coil available for my unit that does not corrode. It is an option to buy, but was never offered to me in 2006. It is coated with tin to avoid the aluminum/copper corrosion. Carrier only sells these tinned units (not an option) in the Southern states since a few years ago. These improved coils cost less than the failure prone ones, but still they are about $1K.
 
Has anyone noticed if the new tinned coils are more reliable?

These improved (made in Mexico correct me if wrong) coils should replace the failure prone units at no charge to US consumers. I wonder if they have a 1000% mark-up like everthing else that is out sourced?

The TXV valve should be easier to repair than an inside coil. It is smaller. A valve has moving parts so it could fail just like a motor. A coil has no moving parts so it should never fail.