The defrost feature is not working. You did the right thing by turning to em heat. You will need to defrost the unit before using as heat pump...but if defrost is broken it will freeze again.
This is either the defrost control board or a sensor depending on unit.
Any suggestions on melting the ice-it's pretty thick and it's in the 20's with a strong wind.
Hair dryers, heat guns, propane heaters etc....but no direct flame....also running the ac is how the unit defrosts itself, but it also turns on the electric heat to compensate when it does that.
If you run the ac for about 3 minutes it will enable a lot of the ice to be knocked off. Careful of fins.
Wish I could help more but without some creative wiring or holding relays in you are stuck thawing manually.
Is the fan running in the top?
Here is where I do not know where to draw the line of what you are comfortable with...
Defrost cycle runs ac circuit, but turns off the condenser fan motor. Once done, it engages heat pump mode and turns fan back on.
This is a case where you could unhook a fan wire...turn ac on...and the unit would defrost quickly. I just do not know your comfort level with the wiring...If fan is blocked by ice and you are not comfortable with unhooking fan wire you will need to shut down and thaw with another heat source.