we recently had an ice storm in the DFW area. Our outside unit is in a shady area that hasn't completely thawed out yet. Therefore, we have significant ice around the unit (and even inside) that hasn't melted. The unit is heating the house just fine but the fan isn't running and frost is building up on the outside coils and on some of the piping inside. What could the problem be?
Sounds like your defrost cycle isn't kicking in. There is a defrost circuit in most newer units that controls that cycle, in which the unit runs in reverse -- literally taking heat from your house to defrost the unit. I'd turn it off ASAP if that's the case since it's just wasting electricity and call a tech to have a look and possibly replace the circuit board. Tell them what's going on ahead of time and maybe they will have the part with them when they come out!