We live in an apartment and lately we've noticed the unit will be running fine on just the heat pump setting ( not aux nor emergency) then in the late evening or middle of the night it will start blowing out cold air and begin cooling off everything that it has previously heated. Its like having the a/c on. Its cold enough that it wakes us up. I then have to get up and push the lever higher until the axillary heat comes on to warm things back up. After awhile it will go back to normal heat pump mode and will sometimes work fine , sometimes start blowing cold again. It seems to run all night. The apartment has come in and checked the temp readings in the day about 5 times now and of course it never acts up when they are here.. as it is intermittent and happens mostly at night. Anyone know what this might be ? Thanks so much