s-type cabin overheating

Hi Guys, have not been in the picture for a while - but now i'm back. Am still driving s-types and recently picked up a 3 L sports edition (2004) with very low mileage. it had been sitting SORN for 7 months. the owner put it through an MOT and replaced the failed parts. I collected it in London and drove it home to scotland through the night. Apart from silly niggles which I can fix I am faced with a massive problem where the vents are streaming 100% pure very heated air into the cabin. The up/down buttons work so what is causing this huge influx of hot, unbearable air ? The seller disguised his ignorance of it and said he would contact the garage that did the MOT. The highheidyun there said he worked for Jag once and the fault was the throttle sensor which needs to be removed and blown out as moisture may have crept in ? So! Where is this sensor and is  he right in his diagnostic assumption ?

Also, does anyone trust Kwik-Fit to do air con checks/top-ups ?