Interior temp sender unit location on 1990 Audi coupe 2.3e B4

Hi i was looking for some help on how to get to the interior temperature sender unit on my 1990 Audi coupe 2.3e B3? Ive been having a bit of a problem with the heater not being very warm lately and would like to get it sorted before winter. Ive flushed the cooling system and heater core, changed the thermostat and fixed a hose before replacing the coolant and bleeding the system. although slightly better than it was the heater isnt warm as it should be. Ive just ordered a interior temperature sender unit off ebay for around £15 but havent got a clue where its located or how to get to it. I cant see anything under the bonnet so my gut feeling is its under the dash. Does anyone know where its located and if i need to remove anything to get to it? Any tips or advice would be helpful and much appreciated. Thanks Ian!!!