2006 Ford explorer/No heat /overheating

Hello, My wife's explorer has stopped blowing hot air when the engine is warmed up and in idle. it just blows cold air/ when I start driving it one of 2 things happen, it will start blowing hot air or it starts to overheat almost instantly, the gauge shoots up. sometimes if I turn the the blower off and on the heat kicks back in (blower works fine it blows cold air when the heat is on when this happens I know to start watching the temp gauge) and temp goes down. 2 times it has worked fine but when I was getting on a on ramp on the autobanh (highway) (right turn) the heat will stop blowing on cold air comes out and over heats again. I pull of to the side and it starts to work again heat blows out temp goes down. I am soldier stationed in Germany and before I get taken to the cleaners at the German ford dealer I would like to have clue whats going I tried explaining it to the German Master Mechanic at Ford and all he kept saying was ya ya heat problem you bring car we fix, any help would greatly be appreciated thanks in advance SSG Leon