Goodday My unit is a 30 000BTU split unit York. It runs for about 15-20mins on hot days when it stops cooling and gradually starts to heat the air. If switched off and turned on after 5 mins. it starts cooling again and the same happens again. The internal thermostat and pcb has been replaced. On cooler days it runs mutch longer for this to happen and on even cooler days it runs continouisly without problems. Hope you can help. Hernus