2016 Prius Driver side only no heat

I’d suggest using a Toyota Techstream (GTS) diagnostic system, or equivalent, to do the diagnostic procedures in the Repair Manual (more info; be sure to use the version on toyota-tech.eu that covers RHD vehicles) under Vehicle Interior: Heating/Air Conditioning: Air Conditioning System: Problem Symptoms Table, in the entry for “Temperature control: Output air temperature is different between left and right registers (the set temperature is the same for both).”

If you have to replace the No. 1 or No. 2 air conditioning radiator damper servo sub-assembly, it’s a big job: the Repair Manual says it’s necessary to remove the air conditioner unit, which requires removing the entire instrument panel, plus equipment to recover and recharge the refrigerant. The manual also mentions that there could be “a wire harness caught between the links of the motors and dampers,” in which case the repair is to “remove [the] pinched wire harness,” without major disassembly or parts replacement.

 

Those servos go haywire on a lot on Lexuses and they fix them for free under a service campaign. I think it was a software uodate? I’d look into that too. Happened to my ‘17 IS350 and it was a free repair when out of warranty.

Mine would work backwards (hot would be cool, cool would be hot) until restarting the car then they were normal.