We bought our home in August 07 with a 17 year old York for the main level which we replaced recently and a 5/6 year old Trane XL13i for the upper level.
The Trane hasn't really operated properly and couldn't keep up with the heatwave that hit the east coast early June. We had an experienced tech examine the policy and he noted decent pressure that would gradually reduce all of a sudden. He also noted that the installer (Sears) did a shoddy job and used the existing line set when switching an R 22 to a R 410 system. He doubts that they flowed nitrogen through the line set.
His diagnosis is that there is contamination in the system and it is restricting the expansion valve in the attic unit. He recommended changing the indoor coil as well as the valve, running a new line set and adding an oversize filter dryer to catch as much of the contamination as possible. After reading his advice I found the invoice of the HVAC service that was completed prior to us buying the house and the tech doing the tune up had noted poor pressure in the attic unit and declared a restricted valve. He changed the filter dryer, the valve and recharged with the recommended level of R 410.
My tech said that this history changes his advice. The fact that this fix did not solve the problem even though the line set was not changed led him to advise not spending what would be approximately a third of the cost of a new system on repairs. Even though the system is 6 years old he recommends scrapping it.
I'd really appreciate your advice, lads. Are there other ways to clean the system out to enable good, long term operation? It seems rather a waste to scrap it.