How do heat pumps and cooling systems differ?
An AC unit only pumps heat in one direction. A heat pump can pump heat in two directions. It can send heat to a space where it can be used to condition it.
Briefly describe how a four way valve allows a heat pump to change modes.
It is a device that allows a heat pump to switch between heating and cooling modes. It can send heat to one coil for cooling mode (outdoor coil) or to the other coil for heating mode (indoor coil).
In the heating mode, which coil acts as the condenser and which coil acts the evaporator?
The indoor coil acts as the condenser and the outdoor coil acts as the evaporator.