I have an central AC issue where the evaporator coil is leaking water. Help!?

The tech I called said that the TXV had to be replaced. The reason he suggested this change of valve was because when he added R410A (freon) he got a head pressure of 420 and a suction of 110, and could not get the suction to rise. Does that sound right/make sense? and if so, about how much will this run me? Thanks!