If your vehicle is showing steering wheel is hard to turn only when the engine is cold, here are the most likely causes and the parts you'll need to fix each one.
Over time, power steering fluid breaks down and thickens, or a slow leak causes the level to drop. When cold, the thick or low fluid prevents the pump from generating enough pressure to assist steering.
A worn, glazed, or loose drive belt becomes stiff when cold and slips on the power steering pump pulley, reducing steering assist until the belt warms up and grips better.
Internal wear in the power steering pump reduces its ability to move cold, thick fluid. As the engine warms up, the fluid thins out and the pump can build pressure more easily.
Internal seals inside the steering rack can harden and shrink when cold, allowing fluid to bypass the assist piston. As the rack warms up, the seals expand and function normally.
If the wrong type of fluid was recently added to the system, it may have an incorrect viscosity that is too thick at cold temperatures, preventing proper flow until it warms up.