We'd need more specific information on the model and year of manufacture.
For example, it could be an issue with the cable controls to the hot/cold flap. A stuck thermostat/another watercooling issue may cause this or the heater matrix may be at fault.
Sometimes it would be neccessary to drive for about 10 miles to properly warm the engine for it to produce heat through the vents.
Pete, January 2010
