radiator fans

Hi there, could someone please explain why Jettas have two fans. Do they cool different systems? How are they related to the A/C? How bad is it if my drivers side fan doesn't work but the other does? Thank you, Irfanzo 2002 Jetta TDI

I have a 07 jetta woflsburg edition that has been overheating on occasion. I took it to the dealership and they said that I need to replace both fans and the the connector at the tune of $1,333. I decided it would be a lot cheaper to do it myself. My only question is what the exactly is this...