Climate control keeps changing the set temperature

what happens if you shut it off at 74 degrees?

 

Is it in "Auto"? This is not a normal Gen2 action.

 

Not at all normal, the controller should retain the pre-set temperature unless the 12v is disconnected or it is physically changed by the operator.

Again, not normal.

Putting these two symptoms together, you are likely losing B+ power to the display (controller), or you may not have it at all. Check your fuses as a first step.

 

So if that bugs you, maybe you should replace the AC amplifier. That is the ECU which controls the HVAC system.

 

I believe the AC amplifier is mounted on the floor of the passenger cabin, below the radio assembly. You would need to remove the plastic trim panel that extends from the floor up to the instrument panel, for access.

 

This is happening on my third Gen Prius also. 2010. Shut off the car, then at cold start up there is minimal display on the temperature control panel, then when you touch a control, like fan speed, the temperature is set to 25 C (in Canada) and you have to put it back down to the temperature you want.
Think it would be the same fix?

 

Hard to know, but as you have 2 Gen 3 Prii, perhaps if you ask your question over in the Gen 3 equivalent forum, the good folk more knowledge in the ways of the Gen 3 may know and be able to help you.

 

I went through 100% identical issues. Turned out battery connection were loose. We got replacement battery from orielly autos parts and tech probably was not aware that prius requires battery connection seated really well and need tighten well

 

Prius are not special in this regard. All cars need both terminal clamps seated and tightened firmly.

 

Yep,
1. clean both posts and terminals
2. seat and tighten terminals
3. spray sealer over both terminals.

Last step is optional for batteries that live in the passenger compartment of the car, since it isn't exposed to the elements as a battery under the hood is. But it should be a good idea to seal them along with ground points to prevent corrosion / bad contact.