So a couple weeks ago I noticed that in our gl450 the radiator fan is always on and on high. It doesn't do this right away when starting it in the morning but once it starts it doesn't stop. Coolant temp shows around 90°C. I think if this goes on the fan or something else will go bad. From what I've read so far it might be ac pressure, some even said mass air flow sensor. I did read the codes but all seem to be unrelated to the fan. When I used a different scan tool there was something about thermostat, anyway to check? There is a tick to the engine but that is probably related to the codes shown. How can I get this fan under control?

Clear all those faults and see which ones recur.

Is your AC running when the fan turns on?

I believe AC is off but will check. When I clear those codes, give it a quick 5-10 minute drive and for the most part they all seem to be back or just about the same ones come back .

There was another thread in which this faults mode was traced to the AC pressure switch which was triggering the AC to run all the time and thus the condenser fan (shared use with radiator fan) to run all the time.

Bingo.

When I was recharging my AC, as soon as I got some refrigerant in, bam the fan turned on high. So it is a pressure sensing switch, not a temperature switch. The switch-on was way too fast to be temperature related.

It could be seeing excess pressure on the high side.

So I checked the level and it was just barely reaching the green on the gauge maybe even a bit under so got some refrigerant to get it in the green and as I was finishing adding it the fan turned on even higher. The level is still in the green. Any other way or place to check refrigerant of other things. Tried looking in the fuse/relay diagram and didn’t notice labeled radiator.

Did we get an answer to this question ?

If your radiator fan doesn't go crazy when AC is off, it is most likely your compressor or some other component of AC system.
How's your AC performance? Does it blow cold air?