Inverter Voltage to compressor

Wait, wait, whoa.

The high-voltage system on the Prius is deliberately isolated from chassis ground. Unlike the 12-volt system, which grounds the (-) side of the battery like any conventional car, the HV system does not have either side connected to ground and, in fact, the system constantly tests for leaks to ground in case the isolation is damaged or deteriorates.

Your only meaningful measurements in the HV system are between one HV lead and another. The Gen 2 compressor has three wires going to it, driving it as an ordinary 3-phase AC motor when it's on. The voitages and waveforms will depend on what speed the car wants to run the compressor at. I don't remember whether the compressor drive comes from the unboosted bus (201 volts nominal, probably not higher than 250) or the boosted one (probably never higher than 500).

Note those are high enough voltages that anybody who wants to take this measurement should be using personal protective equipment and careful procedures.

Measuring from any HV lead to chassis ground might show you some voltage, depending on the maximum allowed leakage current and the impedance of your meter, but it won't have much to do with anything you want to know. If there is any larger leakage current, there will be a diagnostic code reported for it.

This is about Gen 2 ... just to be clear for any future readers, Gen 3's compressor is different, and fed with only two wires carrying 201 volts DC nominal from the battery; the Gen 3 compressor does its own motor control internally.

-Chap