Hi asfixious,
Welcome to the HVAC Group!
On A Trane Heat Pump the suction Line service valve the service ports are located at the outdoor unit. Give the system a thorough visual inspection and even take the cover off and look. It is great that you have cleaned the coils. You need to check the operating pressures after you locate the service ports.
check the voltage and amperage on the motors.
check the operation of all/any safety controls.
check all electrical connections.
check the fins on the condensing unit for straightness.
check the reversing valve operation.
check the defrost control.
check compressor amperage.
check emergency auxiliary heat strips.
replace the air filter.
check condensate drain.
clear any sediment from the drain.
check evaporator coil.
check the thermostat.
Check the temperature drop across the evaporator coil (15-20)
Good Luck!