I have an E220 coupe, and today I noticed that the fan would not come on.

There is only 1 fan in front of the radiator/air con condenser, and one which is behind the radiator, and is ran off of the engine. The one off of the engine was on, but the one in front of the radiator did not come on at all.
I had A/C blasting, outside temp was 28 degrees C, engine temp would go up over the 80 mark and peaked a bit lower than the next line above 80.
I opened the hood and flicked the fan to start but it didn't.

What would I do to diagnose the issue?
When should the fan be going on?

Any help is greatly appreciated