Prius 3, PTC/AUX heaters

You know, I've had the same questions ever since I had my Gen 1 (which also had the PTC heaters, by the way), but it took your message here to actually get me off my butt to go out to the car, plug in Techstream, and watch. It's about -7 C outside here, at the moment.

You don't have to set the temperature to anything specific. The Techstream reading of the air mix position went to 93 (as high as it goes) whenever the inside temperature is appreciably below the temperature I set. Since the lowest my US temperature can be set is 65 F, and it's below 20 F outside, that meant the damper stayed at position 93 throughout my test. The only way I could make it move was to set the temperature on notch lower, to 'LO' (which calls for unconditional cooling), and that swung the damper all the way to position 6, as far as it goes in the other direction. Move the temperature setting back up one notch to 65 F again, and the damper swings fully back to 93.

Presumably, once the interior temperature starts to get near your setpoint, the air mix may modulate to some more intermediate position. But as long as there is much difference between setpoint and reality, the damper will be at one extreme or the other trying to correct it.

What puzzled me at first was that I did not see a nonzero "electric heater active level" under any combination of control settings I tried. They were simply not turning on at all. At last I realized I had the car in ECO mode. I turned that off, and right away, the active level went to 1, and a few seconds later to 2, and then to 3 (the maximum).

It remained at level 3 throughout my testing, which surprised me. I had always understood the PTC heaters to be a stopgap that would cut out as soon as the engine was moderately warm. But I saw them stay right at level 3 even as the engine shut down, having reached 58 C. This was still with my temp setting only at 65 F, and regardless of the blower setting.

As with the air mix damper, I could only get the elements to turn off by setting the temperature to LO, so the damper swings to 6 and the elements, of course, turn off. Raise the setting again one notch back to 65 F and the elements came right back on at level 1. They seemed to have longer delays that time between incrementing to level 2 and then 3, but they still ultimately did.

ECO mode seems to lock them out completely, though, at least as far as I can tell.

A/C did not have to be turned on. That would be a pretty strange requirement....

-Chap

 

Does every 3rd gen Prius have PTC heaters, also in Europe? First I've heard of it...

 

i have never felt any sense of the air getting even slightly warmer in 3 pri over 14 years.

 

Yeah, back when I measured their current draw in my Gen 1, they seemed to be worth about 700 watts when all operating. Not peanuts, and every little bit counts, but that's small compared to the 5300 watts the Gen 1 and 2 heater core is good for once the coolant is warmed up. (I don't have the Gen 3 New Car Features book in front of me for that spec.) I've never been able to say I felt a distinct difference in the air coming out.

I did get the 700 watt figure using an actual meter, so I do know they were coming on!

-Chap

 

probably why early pip adopters tried putting 1,500 watt heaters in the car to preheat, but gave it up as a bad job.

 

Armed with this newfound knowledge, I now turn ECO mode off if I'm starting the car first thing on an icy morning to put on the front defrost before getting out to chip at the windshield. Now that, really, does noticeably help, more than doing the same thing with ECO on.

So, throwing in an extra 700 watts in the right conditions can have a use after all.

-Chap

 

thanks, i have never had eco off, i'll give it a try.