Arrived found unit cycled off. Checked evaporator coil and the blower wheel are clean. Heater is operating. Customer changed filter 16 x 25 x 1. Found water residue on return Plenum. Possibly caused by water condensating off PVC drain line. PVC drain line does not have insulation. Neither does supply Plenum. Checked capacitor, contactor, and pressures. All are within manufacturer specs. Recommend wrapping PVC drain with Arma flex and replacing supply Plenum.