Heat comes on with ac cooling

possible stat failure

is it only in heat? Possibly the heater contactor but I don't believe nordyne uses a contactor. could possibly be the transformer humming? many different strange noises come from units, may want to have it serviced.

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You might have a short going to your reversing valve. Check the temperature of all three lines out of the valve. The one on the left should be cold and the one on the left should be warm hot. . Check voltage to the valve.if it fluctuates that might be the reason for the buzz.

The AC unit outdoors must be running and rejecting heat by its air flowing through it the 2 copper lines are the refrigerant lines, the fatter one should be "beer can cold" if not its low on refrigerant or not running.

It is probably the compressor humming. They can make some funny noises especially on start for a while. If the unit is not cooling it may be the start capacitor or the comressor may be locked up.

If you are referring to a Thermostat, the wiring is normally R is Power (red wire), G is Fan (green wire), W is Heat (white wire), Y is Cooling (black wire). On the Furnace, the two wire from the AC would have 1 going to Y (cooling) on the furnace and the other wire going to C (common). The 2 wire from the AC is generally white and black.

Yes it is. I hear that all the time how this unit does not heat/cool like the old one. Energy efficiency, variable speed motors, your pocket book will thank you!!

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Sounds like it could be a effiency function to warn you that the heat elements are on. Check your thermostat manual and see if you can turn this feature off. If this is not a feature then the thermostat may be wired wrong or something in the circuit may be trying to short out.

I think your problem is poor usage of the device,i.e. overloading the system. try running better cables to your furnace and ac. The reason i am lead to believe that is. If you already hired a pro to come and fix it for you,and he/she could'nt then what else could it be? in my experience ac units use electricity like microwave ovens.and power tools

Things that are not broken: The big relay that powers the compressor often hums or buzzes when the unit is running. Several brands of heat pumps keep their reversing valve "on" any time the thermostat is set for "cool". They buzz, too.

If something really is loose, the only way to fix it is to look at the machine and take off panels until you find what is buzzing.