When I arrived the client stated the AC system was not cooling but he took off the nest thermostat and put a regular one on and it started cooling. I tested the pressure and the split which both were at manufactures specifications. I noticed water in the float switch and found the drain line buried outside and below grade. I recommend clearing the drain line and the client agreed so I cleared it and made sure it was cooling. I reminded the client that the AC system was undersized and that the thermostat he put on was not a correct 2 heat 1 coil heat pump thermostat and I would recommend getting the correct one ASAP. I let the client know to keep an eye on the drain line since it is below grade and if need to we can always run a new drain line with a condensate pump.