Ive noticed today that my new car Fiesta Van Sport 1.5tdci mk7 2015 blows cold air in cabin even though i have not touched anything and then back to hot ? Any ideas please .

Could it be The knob on the fascia is not correctly causing the air-divert flap to move,,,,,,,Solenoid valve on bulk head closing when it feels like it......Interior temp sensor if so what one and where ?

Please help.