I got a call for replacing a T-stat... (for home). The York heat pump... after replace with the new one. I found the blown fuse at the airhandler... changed... now I have the blower up and now the electric heat is temporarily used but the unit outside is not running...
In heating mode : the unit outside not working
In Cooling mode : the unit is working fine...
Q1/ May I have a wiring wrong? With the old t-stat O, B are connected to terminal. With the new t-stat O can connect but not B... so what I should consider?
Q2/ I push the reset button at the unit (contactor) outside in heating mode the unit run fine with Low side = hot... and I release the reset button the unit stop working... So board is defective?

Any advices... thank you.

Sounds like your signal circuit is not making it to the heat pump to activate the contactor. It could be something with the thermostat since you just changed it.

Look at the sticky notes at the beginning of the board to help determine the what the wiring for the thermostat should be.

You did not post the model of the new thermostat. Do so now.

The thermostat you bought to replace the old stat with might not function with a heat pump.

I did check the wires color at the unit to t-stat...
The new T-stat that I bought is not good for this type of heat pump. Like you said: I will looking for another one especially for heat pump.
Thank you for your help... I will let you know the result tomorrow.