Do you have a model number for the fridge?
If it is a known design issue or a regular problem reported by other fridge owners, it could be argued that there maybe a design/quality issue with the fan (and motor?). If this were the case, it may be possible to argue with Westinghouse that the issue experienced is common, appears to be a manufacturing issue (not wear and tear) and therefore should not be expected from a relatively new (4-5 year old) fridge. Thus it may be possible to argue that the fault should come under the Australian Consumer Guarantee.
Also check the user manual to see if there is any maintenance required of the evaporation fan unit, such as annual inspection to remove collected dust, mould, buildups etc. It may be that the fan failed through not meeting the maintenance requirements of the manufacturer. If this was the case, it will be very hard to argue that the fault should come under the Australian Consumer Guarantee.
If there is no history of similar faults or there are no maintenance requirements, then it could either be a wear and tear issue (good quality appliance colling/evaporation fans and their motors should last many years and possibly the expected life of the fridge) or a fault with the fan fitted in the fridge you bought. Such may provide an avenue to negotiate an outcome with Westinghouse such as they pay for the part while you play for the labour. Such offers may be accepted as they share the costs for an appliance which is out of manufacturer warranty but may still be under the Australian Consumer Guarantee. It may be worth trying.
Choice has in the past covered life expectations of some major household appliances. For fridges, Choice found…
Cheaper to replace after 6–20 years
· Budget / entry level: 6 years
· Mid-range: 9 years
· High-end: 13 years
Your fridge would be possibly classed as mid-range and therefore last at least 9 years. It is worth noting, and as outlined above, that the evaporative fan problem you experienced would be considered a minor fault and not impact on the life of the fridge. One would however expect such a part to be very long lasting and not fail prematurely.