I am considering 3 HVAC replacement systems, AS, Carrier and Trane. One (AS) has a R22 a/c unit and two (Carrier & Trane) have 410a a/c units. The refrigerant and suctions lines are imbedded in the wall and ceiling (it's a condo unit) and can not be changed. The Carrier and Trane guy have told me they will flush the lines thoroughly before using the 410a and the AS guy recommends staying with R22.

Any opinions on using 410a in existing, older lines?? Possible mechanical risks?? Would flushing the lines remove all of the old residue??

Thanks,

Vince D.