Folks, we're dealing with a record cold snap.
1) Indications are almost overwhelming that the start caps for the HVAC have gone south for the winter.
2) So the REACTIVE power demand is going through the roof.
3) The RESISTIVE power (true power) is being picked up by the meter -- as is the REACTIVE power. This is why you're getting screwy readings.
4) The HACR rated breaker (100A 240VAC 2-pole) is designed to handle such loads. It would be a VERY rare MAIN breaker that was designed for HVAC dominated loads.
While one might think that the separate legs of 1-phase power can be added to provide a meaningful number/ value -- they CAN'T. You're reading the same current, twice, by working on either side of the neutral tap. So, there's NO 245A load in the system.
The unbalanced nature of the legs (as the HVAC is powered up, the leg imbalance shifts and grows)
is a flaming indication that the cap is bad. In modern HVAC units there's been a tendency to install dual tap capacitors. It features a Common (coded white), and two Hots. (color coded gray and black, typ.)
When it goes bad, it creates big time troubles skewed to only one leg of the power draw. Even if the overall machine is 240VAC, the starting coils are commonly really set for 120VAC ... or some such. (The fan is typically running at only 120VAC. Each unit needs specific inspection to determine exactly what's going on, circuit wise.)
This feature exists because the HVAC unit needs intense starting torque, and because the common hermetic designs actually run cooler than the outside air. (Being bathed in return refrigerant, of course) [This latter aspect makes the electrical engineering of such hermetic units an art away from all other electric motors.]
During the cold snap, the control logic of the HVAC unit may, or may not, provide for the compressor to cut out. I'm going to assume that it's trying its best... and is not cut out.
A more elegant design would have a temperature sensor that would inform the controller that it's too cold to even attempt to spool-up the compressor.
A frustrated compressor can run HOT. This is possible when the coils are entirely ICED OVER. What you end up with is refrigerant flow starvation back at the compressor. The fluid is not even flashing into vapor!
This results in the device just cooking in its own juices -- to include the proximate capacitor.http://www.ebay.com/itm/Dual-Run-Capacit...-/251157955066?
TEMCo sells a range of start and run caps.^^^
There are no end of other players in the market -- and apparently many love to use eBay, too.
As this travail unfolds, I expect that the homeowner is going to find out that they've TRASHED their heat-pump.
Certainly, it needs better HVAC tender mercies than it's seen to date.
What's throwing everyone is the extreme cold. The HVAC guy is probably getting panic calls all over town -- and is TOTALLY lost as to what's going on.
At first glance, it appears that the trouble is the 'booster circuit.' (nee 'back-up')
The real problem goes back to the original design. It needed to have an extreme weather cut-out. Below certain conditions, it's destined to fail -- every time.
The other -- extremely likely -- possibility is that the original install cheesed it on booster wattage. This is to be expected. This can be corrected in the field -- even now!
The HVAC dude needs to get back out there with additional booster coils. (My suspicion.)
In the meantime, the heart of the heat-pump is being destroyed. She's cooking its guts to death. This will ultimately require her to have the entire section replaced in the dead of winter. Perfect.
Being an electrician, everyone expects you to fix simply everthing. Get used to it.
Lastly, big time hum = reactive power issues, usually.