When should valves be adjusted according to Technician A?

The adjustment of valves is critical for ensuring that an engine runs smoothly and efficiently. Both provided conditions for adjusting valves are valid and important.

When the piston is at top dead center (TDC) on the compression stroke, both the intake and exhaust valves for that cylinder should ideally be in a position where they are closed. This allows for an accurate adjustment of the valve lash or clearance, as the camshaft has positioned the rocker arms correctly during this phase of the engine's cycle. Adjusting valves at this point helps to set the correct timing and height of the valve openings, which is crucial for proper engine performance.

In addition, ensuring that both valves are closed means that neither is exerting any pressure or load on the rocker arms at the time of adjustment. This further guarantees precise clearance settings without interference from valve spring tension, leading to a more accurate and effective adjustment.

Therefore, both conditions specified in the question support the accurate and effective adjustment of valves, making the conclusion that both statements are correct a suitable answer.