Found that thermostat that was replaced last November has failed. Found that when thermostat was in cooling mode on the thermostat it was not picking up the o terminal to energize the reversing valve for cooling mode. Replaced Honeywell t-4 thermostat with Honeywell t-6 thermostat. Tested system in cooling mode. Heat pump is working fine at time of service. Honeywell thermostat is a warranty thermostat. Waived diagnostic fee.