I have a split unit train that the outside unit will not come out of heat mode. I checked the voltage on the orange wire and there was voltage. When I removed the orange wire from the outside unit I expected to hear the hissing sounds but heard nothing. I did reachdown and touch the lines and they were very hot. The gas (big) line was hotter than the liquid ( small) line. I think the reversing valve is stuck, but I am not sure. How do I check to make sure the valve is stucks.
When you checked the voltage, did you check from orange to common? Orange to ground may give you a false reading. If voltage is required to energize the reversing valve and you disconnect voltage to it, the reversing valve should switch. If it doesn't, your reversing valve is stuck.