Before performing any maintenance on your heat pump system, shut off all power to both the indoor and outdoor units.
1.Check all wiring connections to ensure they are tight.
2.Remove debris from the unit. On the condenser/compressor, remove the fan cage and fasteners using a screwdriver. By hand, or with a vacuum, clean leaves and other debris.
3.Gently spray the unit with a garden hose, removing dirt, grass clippings, and debris. Do not use a pressure washer as it may cause the coil fins to bend.
4.Clean the blower wheel. The wheel can be found inside the unit and can be accessed using a screwdriver to remove the front panel of the unit. Next, remove the drain panel, which has the flaps that open and close, loosen the coil vent, and gently pull out the blower wheel. Clean the wheel with a garden hose and nozzle. When inserting the wheel back into the unit, ensure that all removed screws have been inserted back where they belong.
5.If you have an old thermostat, check to make sure it’s level. Being off center can alter the accuracy of the internal component.
Sources: http://www.hvac-for-beginners.com/heat-pump-maintenance.html, https://www.youtube.com/watch?v=OiEcHHzz8YU