That would depend on what is causing the smell. If it is something spilt over , some charcoal would clear the smell in no time.

If it is mouldy smell due to water leakages, you would need to rectify the leak first. Drying out would solve the problem, of course some air freshener works.

If smell is from the A/C system, that could mean the evaporator requires servicing. Accumulation of dirt etc on the cooling coils has resulted in the bad smell.

If the smell is from cushions and carpets, heat cleaning is the best way to go about.