What is the first thing to check when the air conditioner suddenly stops working on 2003 Toyota Tacoma

Dealer says replace the relay first. How do I check that the relay is working without having to pay for that expensive 'non-returnable electric component'?

Asked by for the 2003 Toyota Tacoma
alot of relays are generic just plug that relay in a slot with an identical one and if that component dies youve got a bad relay
Where is he relay? Is it the 50 Amp square 'fuse' in the engine compartment box?
yes that sounds about right their may even be a wiring diagram on the side