i used an aircon cleaner, not the forte one tho, the instructions with mine were turn air con on full(engine running), close all windows, fold front seats all the way forwards, set canister going on rear floorwell, close door and retreat for 10 mins (or 5mins after canister was empty) then open car and alow to ventilate (its not adviseable to breathe the stuff in)
i set mine to 21 when i did it, the instructions i had dident say what temp to set so i just put it half way, worked ok for me, i had a mouldy smell before using it and it has been fresh ever since (6 months ago)
no problem, it is behind the plastic cover where the windscreen wipers are, you only need to take off the passenger side (a few screws and the rubber seal in the engine bay) and you will see the filter :thumbs:
If your 156 is post 2001, with body coloured bumper inserts and door mirrors, then you have the later style cabin filter. There are 2 of them and they are accessed, fairly awkwardly, from the bottom of the heater assembly from the LH footwell.
The cabin filters aren't overdue a change, are they? That can produce ventillation problems also.