1996 hiace over heating

Hi all.
First time posting so.not sure I've done this correctly but......
Just acquired a 1996 hiace with a 1kz-te. Had a few issues with overheating in the van. The radiator cap was faulty and the air in the radiator wasn't all that helpful either. With all that sorted it's about 80% better But what I've also found is there is a second radiator that sits horizontal in front of where the main radiator is mounted. Now there is a fan on top of this that doesn't seem to be working. Can anyone tell me what operates this and when it's meant to operate??

I have the same engine with two rads as you have found can only assume its the temp sensor that works the fan , fitted a digital temp gauge to mine am currently fitting a new thermostat, original has done 100,000 miles pig of a job over heating can be a problem on these engines 76 deg thermostat on Hiace all other applications seem to have 82deg just make sure everything is working correctly eg viscose fan electric fan flush system and use Toyota red coolant. GPW has gone the extra mile and designed a superb conversion that improves coolant flow see posts.