I have bought the heater part for my ford fiesta 1998?

There is no flap for the hot air!! the hot water from the engine flows through the heater when you select "hot" on the temp dial, as you mention four jubilee clips, it sounds like you have the heater control valve, as this has four water pipes going to/from it, it also has an electric plug and is held down with a couple of bolts, it's an easy to replace item for someone with basic car maintenance skills

nigel
November 2010

if you can, undo the clips, and change the reflector.

hope it helps
November 2010