Performed diagnostic on 16yr old carrier unit, upon arrival customer stated unit outside wasn’t coming on just buzzing, checked both tstats, cycled to ac mode, went to attic to inspect furnace, found furnace heavily rusted, explain could cause issues in winter, blower motor has been replaced at some point, blower cap checked good, found two dirty filters, recommend replacing both filters, evaporator coil heavily rusted, explained could cause future leaks, found one of the zone dampers are stuck half way open, recommend replacing zone dampers, also noticed unit doesn’t have a bypass , explain system is zoned and requires a bypass to help relieve pressure when only one zone is calling to prevent dampers from failing, upon checking outdoor unit found not running making real loud buzzing noise,condenser coil impacted, recommend chemical cleaning, customer had a lock on disconnect box, didn’t have key and gave permission to cut lock, removed lock , found contactor buzzing, recommend replaci