Gen3 Prius - Is The Heating On When It's Off?

[johalareewi]

After a few years and many miles, I have often wondered if the cabin heating is still on even when the unit is OFF.

When the OFF button is pressed, the fan controls, temperature setting etc. all vanish from the display giving the impression that everything is off. But, there is still warm air coming from the vents.

Also when it is cold and I have left the temperature setting unusually high (say 22C) the day before.

The next day, the car still gets very warm and the mpgs drop even though the heating controls are still off.

[YarisHybrid2016]

Hmm interesting.

As I understand it, the Prius uses peltier devices for cold/hot air (totally electric).

Whilst the Yaris uses engine heat (water coolant via heat exchanger?) if I push OFF, then it is OFF.

There is some parasitic airflow due to ram effect when in motion, but this is entirely seperate from anything else. Setting the system to recirc should stop this.

I did find that you can still redirect the airflow with the system off! :)

[IanIanIanIan]

The Peltier device was only used in the prototype unfortunately.

For all production Prius (Prii?) the only source of heat is the engine.

[kithmo]

I first noticed this on SWMBO's Gen 2, the only thing that seems to go off when you turn the system off is the fan. We were belting up the M1 one warm afternoon with the system off and it got very warm in the car, warm air was coming out of the screen and footwell vents. When we put the system back on (to cool the car), we noticed she had previously had it set on the hottest temp the night before and when we turned it down, then off, the vent temps went down. I subsequently tried it on the Gen 3 I had at the time and found it behaved exactly the same. If I put the temp up to a high setting then turned the system off, when the engine had warmed up there was hot air coming out. The Prius+ does it to some extent but not as much, I suspect it may have a different routing of the air through the ducts.

I found that after this if I set the temp as near as possible to ambient, so it's not trying to heat or cool, then turned off the system, I got the best mpgs. Pretty cold in winter and some demisting problems though.

[MEP's Yaris GS]

The system does 'switch off', but leaves the heater selector in the position its in when turned off. If you had heat on full then this be fully open, and heat will come through as air is pushed through with the car being in motion. If it was on low then the heater matrix will be shut off.

Its no different to any car with manual heating where you have the heat on full the journey before and just turn the fan to off.

[johalareewi]

I thought the same, but like kithmo, I noticed that the temperature setting seems to be honored even though the auto system is off.

If you set the temperature higher than air temp then turn the system off you still get warm air until the cabin has heated up.

[MEP's Yaris GS]

If you set the temperature higher than air temp then turn the system off you still get warm air until the cabin has heated up.

And you will continue to get hot air until it becomes unbearable, as it won't ease the heat off because the system is turned off.