Depending on your thermostat wiring and unit/thermostat, you should have a yellow wire to bring in the compressor/cond. fan. Some thermostats will have one terminal for both heat and cool on a HP for this or you could have one that requires a jumper to the yellow wire/Y terminal to another one... I am assuming since the heat strip comes on that the indoor fan works as well which would mean you either have 1 R or RC and RH are jumped accordingly. I would check in the thermostat instructions the correct configuration for a Heat Pump with an Aux Electric backup and make sure it is hooked up correctly.