Here is what I do - I had one today. My meter reads amps through meter. I leave the box plugged in, remove the board cover. I touch one meter lead to line, then the other meter lead to the defrost on the power input plug. If I read amperage through the meter, then the heater is good, the defrost thermo is good, and I am looking at either a bad board or a bad thermistor. Don't forget, if that thermistor (the one on the evaporator coil) is bad, unit will not defrost. I have never had any board short outs or anything. Good reason to do it this way - if unit is frozen, then it is difficult to pull front panel, you have to thaw first. If I find heater is bad (which it usually is), then I give customer a choice. They can have me thaw it out and pay me for my time, or Let it thaw out and I can come back. Either way, I win. If I steam out unit, I charge them for it. If they want to do it themselves, It saves me time that I can do another call or two with. If it is a far call (distance wise), then I don't give them a choice, I thaw it out.
Thats funny , Ryan. The GE Service school I went to, the trainer showed us how to do this. He was a former field tech, and he said this was the best way to check. I have been doing this for years. I guess every trainer for GE has his own opinions. But, seriously, I haven't had a problem doing it this way and it does give you a fast answer. Only time I don't pull the box is if the floor is soft linolium or it is too tight in wall space. Then, I will take the panel off and check the heater from there.