Re: HVAC Issues - Diagnosis help
The first generation Seq. used a valve to allow coolant to the heater core, but I don't think the 2nd gen has one. The trouble with any used car is finding out what has work has been done on it. I haven't had to work on the cooling system on my 2017 but I had a similar problem on my 2002 after changing the coolant. It was air in the system that eventually worked its way out. Raising the front of the vehicle helped get the air out of the rear HVAC.
As far as I can tell from the shop manual, there isn't a special procedure for adding coolant to the gen 2 Seq. Basically fill it up and squeeze the radiator hoses to work the air out. My guess is that someone has opened up the system and there is air in it, since you don't have heat in the rear and only partial in the front. It is was a problem with the dampers, I think it wouldn't affect both the front and rear... unless there is something going on with the HVAC computer control system.
Good luck! Let us know what you find out.
2002 Sequoia SR5 4WD & 2017 Sequoia SR5 4WD