How long approximately do the DTC N.O. contacts stay closed during the switching process to heat mode?

The correct answer reflects the typical duration that the DTC (Dynamic Temperature Control) normally open contacts remain closed during the switching process to heat mode. In most heat pump systems, particularly during the transition phase to ensure proper operation and to minimize stress on the system, the contacts are designed to remain closed for approximately 5 seconds. This time allows the system to stabilize, ensuring that the transition to heat mode is controlled and that there is no abrupt change that could lead to inefficiencies or potential mechanical issues.

The choice of 5 seconds is optimal for allowing various components, such as the compressor and reversing valve, to start operating effectively without risking damage or improper cycling. Other options suggest durations that are either too short or excessively long, which would not align with the proper engineering design of HVAC systems in terms of operational efficiency and reliability.