4 months ago, had a new A/C system (handler, condenser, & lines) installed to existing ducts. No issues until recently. With temperatures rising in south FL, the unit would run all day long never lowering temp below 80 (therm set to 78). Install company sends tech out, adds gas, but finds and shows me that the connection to the plenum(return) was too small(not drawing enough air) and they needed to "redo" it. The unit was attached to old plenum opening (19x16), which was 2/3 the size of new unit opening (19x23), but the facing side of the plenum (20x28) is large enough for the new unit opening (just never enlarged at installation, even though installation manual called for larger opening). Looking closer, I noticed leaks (cracks & gaps) at both connections to the return and supply sides of the new unit and notified them. Now they want to charge $$$ me to put in a new plenum, but come out and only make the opening bigger and reseal connections & leaks. After inspecting their work, after they left, I found a leak in "resealed" supply connection. Notified them immediately, and haven't received a return call in over a day. Bad Install or Legitimate Repair?