Where can i find the engine coolant temp sensor, fan switch, thermostat housing

I am not a mechanic, but I own a 1999 Acura 3.2 TL & had to have the thermostat and heat sensor replaced. I watched the mechanic replace them and he had to take the cover where the air filter goes off & the thermostat went @ the other end of the hose that's connected to the filter cover.ss