I have a GE side by side Frig-Freezer that ices up. I defrosted the coils and changed the heater. The GE replacement heater was a 2 sides heater as opposed to the original single. It worked for a few weeks and now its iced up again. The tubes are clear. What else could be causing the problem or how would I know if the heater is working?

Your 'fridge has a defrost timer that runs the heater. You need to locate that (hopefully there is a wiring diagram somewhere attached to your 'fridge). Usually you can rotate it manually until it clicks. If not, see what you can do with it. If worst comes to worst, you can bypass the timer with a wire. Be careful not to electrocute yourself. If you aren't comfortable working around electricity, call someone who is.

If the defrost timer is not working, you must replace it. You can also check for continuity through the heater using a multimeter. If you have continuity and you have power to the heater (you can attach a couple of leads and check for voltage using the multmeter), then the heater has to work. Use the wiring diagram to figure out where to connect the leads. You'll probably have to break the circuit on one end of the heater in order to measure continuity through the heater and not through the rest of the circuitry.