What runs the AC in a PiP?

It's the EV battery, if you sit with the AC on long enough, you'll see the EV range go down. If you have no EV range left, and sit with the AC on, you'll see the hybrid battery indicator go down, somewhere below the half way point, the engine will run for a while to charge up the battery a little to continue to run the AC.

 

Yes, it's definitely the traction battery. You can see the accessory power load via an OBD-II reader, and I've seen that go up to around 1kW or so when the compressor is running.

 

It's the same as the regular Prius; the HV battery.

Watch what happens to your predicted EV range when you hit the AC Auto button. Mine, for example, when I start out with AC off, might predict something like 11.9 miles. The moment I turn on the AC, it will drop to 10 point something. It seems to be about 10%. Turn off the AC and the expected range goes back up.

 

If you want detail, jack Kelly at Weber Auto has this video on the gen 2.

Powering the A/C compressor is discussed from 15:10 to 17;00.

 

If you leave the car in "Ready" mode parked up with the AC on, you will certainly see the EV range go down after 10 minutes or so.

 

a better way to know if the engine is running is to watch the mpg gauge. it will be fluctuating, unless you come to a standstill.
my battery definitely drops with the a/c on, but is hard to notice when moving, as it is dropping anyway.

 

Yes, the Traction Battery supplies the power, however I doubt that it directly runs the A/C. What it does is to provide 12 volt charging to run all the 12 related devices, computer, lights, displays, seat heater, etc, and A/C. Remember the discussions about using the car as a 110v source using a 12 volt inverter. The A/C does not run on the Traction Battery 600v (?) output

 

According to this thread, it's running at around 200V from the DC-AC inverter:

How many volts does the GEN III AC Compressor run at? | PriusChat

12V DC wouldn't be much good for running an A/C compressor. It's probably an AC motor driving the compressor - similar to a domestic A/C unit, which would typically run on 220-240V AC mains power. This would explain why non-hybrid cars still have belt-driven compressors, as there's no readily available high-voltage supply with sufficient power to drive it electrically.

 

In Gen 4 I believe it gets the 207 VDC from the HV Battery and inverts it to AC in the Compressor housing. (in Gen2 the DC to AC intverter was part of the Big Inverter)

 

Yeah, if that compressor had to run on 12V, the wires would have to be huge to handle the enormous amperage required to deliver enough power.