I have a lennox heat pump and when it is turned on in the heat mode the head pressure goes up 500psi and compressor starts to over amp but when it is turned over to coolling the unit runs fine it is a 410a unit

You have a bad txv or a restriction at the piston on the out door unit.

Is your indoor fan running during this time in the heat mode? And is the filter clean, possibility of low or no air movement?

Thermostats can change the pressures if they are bad on heatpumps might be the thermostat.

Thermostats can change the pressures if they are bad on heatpumps might be the thermostat


Makes no common sense.