Just bought a mondeo 2.0 si 1998 as a cheap run around for a few months but the heater is not working . The fan blows but only a small amount of air comes out of the demister vent on the sceen and its always cold.When i turn the switch to make it blow out the main vents or into the footwell nothing happens it just still blows through the demister vent. Thanks in advance for any help.