My heat punp fan runs constantly but the unit does not come on and I have little or no heat

"My heat punp fan runs constantly but the unit does not come on"--I assume you mean the air handler fan runs but the condenser fan (outside unit) does not-Correct? Could be low Freon, electrical issue, bad contactor, bad compressor. If you do not have basic diagnostic tools, VOM and Ammeter , for example, you will need a service technician.

If you have it set for "emergency heat" the outdoor unit will not run. If there is electric strip heat installed in the air handler, it should be running.