RX300 2003 and 120kmiles.
A/C problem (and it is hot outside): cold air on left side and left center but warm air on right side and right center. The 3 Servo motors all move in what looks like their normal patterns as best as I can see. I get a DTC 21 which is the solar sensor. Blower works and speed adjusts normally.

What I find very confusing is the cold/warm split down the middle. I'm lost.
Can an air door be broken in the middle? How can the solar sensor cause this split a/c condition?

[I'll post a second about the solar sensor as I don't know how to get it out so as to test it.]

 

Solved. Twas low on Freon. Topped it off and all is well.

I had looked at the sight gauge and it was foamy. The Air was plenty cold on the left side so I figured the Freon was only a tad low but but working. That was wrong. The RX300 has plastic divider down the center line of the HVAC evap and heater unit. But he Heater core and the AC Evaporator extend the full width of the unit.

Apparently what happened to my is there was enough Freon entering the Evaporator on the left side that it cooled that side but by the time the freon got to the right side it had already warmed up from the cabin air being blow through it.

And yes I know for sure the system has plastic dividers in the center as I drilled holes in the sides to pop a 5.5 mm bore scope video camera in to look.

Also for enquirering minds there is a metal screen across the top of the unit that would catch any coins, paperclips, etc that might fall into the vents thus preventing expensive repairs.

 

Yep, the point of entry to the evaporator is where most of the expansion (cooling) takes place, so if the system is low on refrigerant, only the first half of the evaporator gets cold. I didn't know that the divider was so close to the evaporator that the air wouldn't mix properly before separating into the left and right ducts. Useful info to keep in mind.