The heater isnt working on a friends mondeo. The fan is working but only blows cold air even with a hot engine. Is it possible to get an airlock in the heater pipes or heater unit. I dont know if the coolant has been changed recently or has suffered a leak which may have needed topping up.
The first thing to do is make sure the coolant is full. If it is, feel both heater core hoses when the engine is at operating temp. With the heater on, both should be hot. If only one is hot, flush the heater core. If both are hot, check the blend air door.