Need help A/C and heat pump combo. .Unit cools just fine but when off position has humming noise. Only way to stop is to remove 110 power.Called Dometic they said control board was issue but no longer available to used #3316234.700. I ordered and replaced following exact instructions except i do not have a outside temp sensor wire from the unit even though heat would not work on original board when below freezing. upon operation via thermostat shows code E4 which it would not clear using instructions but when fan on and cool selected heap pump would come on and when select heat heat pump would go off. Called Dometic and was told freeze sensor or thermostat defective so i ordered another complete board assy. Installed and have the same issue. Again Called Dometic and they said could not help as support was not knowable to that degree and could not tell me if not having outside temp sensor could cause this problem. I asked if this board was correct for my unit and they replied it should work on a heatpump A?C unit.
Hopefully someone here has had same issue and can help trouble shoot this problem. also if i need to order outside temp sensor which is correct for this new control board?
Thanks Curley
What year and model of coach do you have?
1995 U300. I removed the cover and found factory installed ambient sensor wired into junction box on top so it does have one.Not sure this is factory unit as I purchased coach used.