Arrived on site to diagnose a non operating system. Clients had home warranty out and could not fix issues. Stated they had a shortage due to past owners dog chewed up condenser thermostat wires. Upon arrival system would. Or operate or have power coming in. Thermostat is bad and failing already recommend replacing thermostat. Found system with no filter as it was in the return plenum as it was not the right size and fall in. Found blower assembly hammered, and blower wheel dirty, motor is leaking oil and has layer of dirt and oil.Found someone has bypassed the Low voltage door switch as it it currently cut off. Advised that is a safety concern. They need that replaced or repaired immediately. Test for voltage was not getting none but was getting 120v at pig tail plug in. Replaced a transformer and now had power in furnace as I got blower motor working and operational. Went to out door unit found condenser thermostat wires were chewed up and exposed causing electrical shortages and why