Heat pump performing way below specification
I have a problem with my heat pump and I am hoping that experienced forum members could provide me with 1) confirmation that I do have a problem and 2) what questions and investigation areas I should insist that the service tech address.
I have a 2 year old Carrier hybrid system (ARI# 3261198) that seems to be using twice as much electricity as it should. The 1993 built house is 3 levels and 3,400 sq. ft. and the HP is oversized by the installer's own admission (manual J = 3.5 ton). There are several symptoms that lead me to believe there is a problem: 1) when the outside temperature is 45-50F and running in Hi stage, it typically takes 50-55 minutes for each degree change in the house; 2) when I raise the thermostat one degree (outside=46/47F) to activate the HP, it starts in low stage (half fan speed) and 5-6 minutes the vent temp slowly raises to about 83-84F, then abruptly drops to ambient. At this point the system shifts to Hi stage (full speed blower) and ~5 minute ramp to 84-85F and stays there for about 1 hour. 3) The last indicator is the power bill. The balance point was set at 37F the first winter and 45F for the one just ending. With the 45F balance point, I spent $25 less this winter than last, even though this most recent winter was colder (3677 vs. 3377 heating degree days). So, is this enough to confirm that the system is broken? What should I say to the tech to convince him/her that there is a problem and what should I insist that they investigate and/or correct? I don't want to pay a service call only to get a "no problem found".
Other details that may be helpful: location is the greater Seattle area; winter rates = $0.09/kWh, $1.23/therm; setback to 63F at night, increasing 2F at 5AM, 2PM, and 4PM for afternoon/evening temp = 69F.
Thank you for any assistance,