warm air...how?

Even in non-Primes, the car can turn the compressor on at times without you selecting AC and without lighting an AC indicator. The defog settings do that.

I suspect that's exactly what they do in a Prime when you ask for heat. Most drivers are just going to expect heat to happen when they ask for heat, and would not think to press an AC button to get it. It's an astute question to ask "hey, doesn't the heat pump use the same compressor as the AC?" but I am sure Toyota does not expect most drivers to be thinking that deep under the hood.

 

Correct me if I'm wrong, but doesn't the Prime uses a heat pump and engine heat if needed when OAT is below a certain temperature?

 

The main thing to remember about a Prius is that it is a car run by computers, based on suggestions from the driver. Most of the 'controls' in the car are game-controller inputs telling a computer what you think you would like. There are very few controls that 'force' the car to do anything.

While I don't have a 2023 Prime, i strongly suspect the car runs its own HVAC system its own way, including running the heat pump compressor or not running it as circumstances dictate, and what you do with the AC button merely expresses your preference about whether you would like energy to be used keeping you cool.

 

The heat pump only heats down to an outside temp of 14F(-10C); has to use the engine under that. The system can fire up the engine for heat at other times, such as with the defog turned on.

The AC button doesn't force the compressor to run. It just tells these auto climate systems that it is okay to use the compressor for cooling.

What you see for current draw depends on set temperature and outside temperature. Yes, you should see the current increase when the compressor comes on for heat. Depending on the temperature delta between out and in, the draw may not be high. These compressors are variable speed, not on or off, and when heating, the waste heat from the compressor running is put to use. Running the AC at max cold on a hot day will draw more than calling for a few degrees of heat.

Also, the HVAC compressor is used for cooling the battery. There is that potential draw going on.

Another quirk of these auto climate systems. Once the set temp is reached in the cabin, it only adds enough heat to the output to maintain it. To most, that reduced heat feels like cold air coming out. Unless you overrode the fan speed, the system will turn that down along with the heat output to reduce that cold air feeling.

 

In gen 3, there is a PID you can observe with an OBD-II scan tool, showing the watts of power being sent to the (variable speed) AC compressor at any given moment. I would be surprised if there isn't the same PID for heat pump compressor power in the Prime.

 

I test drove another 2024 Prius (not PHEV) last night because I wanted to experience it in the cold and dark. I didn’t feel as warm as I do in my 2009 for some reason. The heated steering wheel was nice. I turned the heated seat on but wasn’t feeling much. Maybe I didn’t put it on high enough.

I just read thru this thread. What’s the most efficient way to keep warm in this car keeping in mind fuel economy and wanting warmth as fast as possible? Obviously turn heated steering wheel and seats on but what I just read confused me regarding best way to keep warm air flowing. When I was trying to trouble shoot I actually pressed the AC button since that’s what I do with my 2009.

Next I tried testing a 2023 Prime for the heck of it but it was dead. They had to jump start it. : }

 

Did they really make it that much weirder in the PHEVs?

I mean in our car, we push the 'AUTO' button, turn the ring left for cooler and right for warmer.

And it just does it, so we rarely need to even do the above.

 

Heat pumps aren't much good when it goes way below zero in our Canadian winters. I'm sure the engine heat is also being used. Mine is toasty inside, even when it's -20 or colder. But I have a cardboard partition ahead of my radiator.

I see interior heating as a big drawback in non-hybrid EVs. Regardless of whether they use heat pumps or electric heating elements, range is going to take a big hit.

 

Don't have a Prius. I just see the same behavior from the Outback, and it doesn't have an Eco HVAC setting. If a home vent was directed at you all the time, you would likely experience the same there too. Your skin is not a precision thermometer. Air that is less warm than what it was exposed to previously is reported as colder. it does not mean the HVAC isn't heating the air.

 

If Google generative A.I. is correct, the 2024 Prius Prime uses an electric heating element for interior heat in addition to the heat pump and engine heat. I was a bit surprised by that; electric heat is quite detrimental to driving economy, but I suppose it's just temporary until the engine warms up. I can't see the heat pump being much use in temperatures far below zero.

Here's something I snipped:
The 2024 Prius Prime electric heater primarily draws power directly from the car's battery to generate heat, essentially acting like a resistance heater, and can also utilize a "battery heating system" within the battery pack itself to maintain optimal battery temperature in cold weather, which indirectly contributes to better heating performance; this allows for cabin heating while primarily running in electric vehicle (EV) mode without significantly impacting the driving range

 

The gen2 had resistance heaters to help cabin heat while the engine warmed up. I never noticed it.

 

I would definitely compare any generative AI answer about the system to what the New Car Features manual says and the wiring diagram shows. I haven't looked at those for a Prime. But gen AI hallucinates all the time, and it's especially easy when it has ingested so much writing about the resistance heat in other Prius generations.

 

I guess that should mean I'll get instant heat when I start my car in subzero temperatures,
but I can't say I've noticed that so far.

 

I think not every region had them. And the G5 doesn't at all.

 

In the generations that had them, they were in the 700 or 800 watt ballpark. Compared to the roughly 5,300 watts of heat you'd get from the heater core when the coolant was hot, 700 or 800 is imperceptible (in my experience). I can tell the difference in how fast a fogged windshield clears, but the air doesn't feel warm at all to my skin.