90 sub legacy 2.2 5spd- I noticed that only one (passenger side) radiator fans turns on. Are they both supposed to come on at the same time? If so, do they have individual relays? Where do I start looking?

Yes I belive so... Start following the wires back and look for anything physical like cracked, split, torn wires and check your connections at the fan motor to see if your getting and juice.

 

You should be able to find a wireing diagram with a proper Google search and that helps out, wireing is a pain but this looks to be an easy fix.

 

Here's a start for the cooling fans: http://www.ultimatesubaru.org/forum/showthread.php?t=75457

I have been working on a similar issue. The passenger side fan is the sub-fan, the drivers side is the main fan. In order to check if the main fan is working, the best way is to jumper the fan. Unplug the connector to the fan. You will see three contact points. 1 is the ground, the black wire i believe, the other two are low and high speed fan operation. Run wires from the fan connector straight to the battery. If the fan operates, the fan is good. You could have a bad relay. The relays are located under the hood on the drivers side fuse box. The fuse box cover should show the relay locations. One fan, the sub fan I believe, operates when the AC is on, the other main fan is for standard cooling I believe.

Roger that, Fuz. I own a 94 legacy and I'm still not sure myself which fan operates when and for what purpose. Just been doing some reading in the ol' Haynes manual.