Responded to no heat call for 1-year-old furnace with blank thermostat. Discovered blown 3-amp fuse on EIM module caused by outdoor unit in heat pump mode. Diagnosed high pressure issue (550 psi liquid line) with system tripping on high limit. Replaced dirty air filter but determined system has a restriction in refrigerant flow, likely in reversing valve or filter dryer. Scheduled follow-up service to pinpoint exact restriction location and replace necessary components.
