ok what you need to do is get the heater matrix out the car, pull back your carpets and get a torch , you will see four fixings holding the heater into the car. also undo the water pipes in the engine bay going through to the inside of the car. disconect the control cables to the heater aswell ( they direct the hot air and temperature) once thats out all should be come clear. there is a seam up in there that is usually coverd in seam sealer and rusty. the bowl so to speak will become clearand you will probably find it full of leaves etc and rusty. In most cases it is a welding job but i guess you could try sealer but it wount last very long.
also check your drain from the bottom of the bowl isnt blocked up, this is the rubber part you will see from the engine bay just up from the heater pipes and in the middle of the bowl.
good luck, just get stcuk in and you will be fine there isnt alot to get wrong with these old escorts.
jamie
