1996 BMW 318 Engine Cooling

I originally had a heater hose leaking which was diagnosed to a broken water outlet valve which was replaced. It was still overheating so they replaced the thermostat and water pump. Still overheating so they replaced the fan control switch. I noticed the electric cooling fan never comes on no matter how hot it gets. It takes about 7 minutes to overheat from completely cold and I never get any hot air out of vents. About three years ago I was having a overheating problem and BMW replaced a fan relay and a fan diode relay. Could this be the problem and does that electric cooling come on when the temperature rises. Since I replaced the fan control switch where are those relays located? Any other thoughts would be greatly appreciated.

Thank You