i have a 1990 ducato motorhome and the heater blows out hot air only no cold air.

these are gonna sound like stupid questions:- have you tried turning the controls to cold? have you opened all the vents? have you checked that the heater is not set to re-cycle. are there any external obstructions to the free flow of air such as leaves in the vents etc.? if none of these are the cause, the fault must be in the dash board. either the control has somehow become disconnected or the air ducts are blocked. best of luck. ian

I'm not sure if the flow valve is under the bonnet or behind the dash, if you can locate it see if the cable is attached, get someone to work it & assuming it moves check its going as far as it can. If the cable isn't attached manually move the lever all the way over & check if its 'fixed' the fault