So in the process of converting from R12 to R134A, I noticed the passenger fan behind the radiator does not engage. The driver's side fan is on when the A/C is on. I've replaced the fan from the pickNpull and it still doesn't work. 

 

I've read some confusing content that only one fan comes on and it's if the car is overheating. 

 

Can someone clarify? Should I be worried about the other fan? 

 

It's worth mentioning the car does not overheat. Ever.

 

cheers fellas! 

On later models there are two green plugs under the dash on the drivers side near the column. Connecting those then turning the key ON puts the ECU in Test Mode and will cause all of the relays and solenoids in the car to cycle, including the fan relays.

 

Generally only one fan (secondary or sub fan) will run with the AC running. The other fan (main fan) will only run if the coolant temp is above a certain point, but still well below the point of overheating. Generally just letting the car idle (no AC) will cause the main fan to cycle after the engine gets fully warmed up.

If the engine is warmed up and the AC is on the main fan and sub fan may run at the same time, but not always.

There is a sub-fan (passenger side fan) short connector that ties both fans together and causes them to come on together.  It's normally located behind the passenger side headlight.  The diagram below shows the connector.  See if there is a jumper connector in there.  If not, try jumpering the wires and see if both fans operate together when the green diagnostic connectors are connected.

 

http://main.experiencetherave.com/subaru_manual_scans/FSM_Scans/1992_legacy_radiator_fan_wiring_diagram.pdf