i have EXACTLY the same problem on my 1998 2.8 V6 Auto Ghia X (with climate control) I have taken the servo motors off the side of the box (basically there are 2 on the right hand side). The lower one operates on a large toothed (cogged) half moon which is for the air flow direction (footwelll, windscreen, vents etc). The upper one operates on a cogged wheel which is almost entirely hidden inside the matrix and only a small part can be seen through a hole where the servo motor operates on this wheel. When removed, both servo motors operate normally, and changing the temp or flow direction operates the appropriate servo. However, when i manually rotated the cog which controls the heat, it failed to make any difference to temp and consequently i have established that the fault must lie within the matrix unit. I assume this controls a valve which allows the coolant to flow through the matrix and thus heat. I am guessing it is a fairly big job to remove the matrix completely, but i guess that is probably the only way to sort the problem. Alternatively, because of the high costs of repair/replacement, i have considered bridging the inlet/outlet pipes connected to the matrix inside the engine bay against the bulkhead, and thereby not passing coolant at all through the heater matrix. I know that would mean no hot air in the car, but at least i wouldnt be sweltering everytime i drive it! If anyone else can shed further light on the problem i would much appreciate it! Many thanks