After RTH6400 installation heat strip is no longer actuated

Your question makes no sense. You dont have a heat pump with ONLY emergency heat. Is it working or not???

Some blowers shut off depending on the system. Do you have electric hest strips inside? If not the blower will shut off. The outdoor fan should not be running if in defrost mode. If you have heat strips then you likely have low voltage wiring crossed

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Aug 22, 2010 - programmable thermostat, error codes, american standard: James, I am not familiar with that stat set up,short of goggle/yahoo the codes may ...

It's possible the "brain" thinks it can still supply some heat. Other wise there is a wiring problem or thermostat switch problem. Installed recently? Never used emergency heat before? What is your emergency heat type, gas or electric? Are you sure they are working. If not the "brain" senses and uses the only source available: heat pump. Thermostat? probably Honeywell? If so call Mfg customer service. Warranty on thermostat or heat pump? If so call customer service. Call your installer.

going out on a safety. try replacing capacitors

How old is the unit? Heat pumps don't work when it's real cold, you know it's limits. If it's not real cold outside, then it may be low on gas or such and need a service call.

If you are using strip heat as seperate mode you must install a fan isolation relay which would be energized by emergency ht mode of stat.

What relay does he click?

I see what you see also in the manual. The difference is the Heat Strip package that part is optional and the 600212-001 with the optional heat strips becomes the new 600315-001 I talked to Dometic Duo-Therm and the models are the same but they both are not heat pumps but the new heat strip package comes on when told to go into heat mode when you change the thermostat to heat. The part you purchased will fit both model numbers you listed for your roof top air conditioner. Thanks, Sea Breeze

The unit is probably to small for theare you are trying to heat.

When the Aux HT light came on that meant the heat pump could not keep up with the demand for heat. (Probably due to extreme cold, or undersized unit.)

If yu have heat, then at least one heat strip is operating. If you have multiple heatstrips, one or more could be malfuncioning.

Or it could simpy be to cold/to small fr your area and not able to keep up.

How many square foot are you trying to heat?
What is the outside temp?
What is the inside temp?
What size unit (BTU output) do you have?