HVAC relays and sequencers make or break the electrical connections in an HVAC system and ensure that components start or stop in the correct order and timing. HVAC switching relays respond to control signals and make or break electrical connections. HVAC time delay relays wait a pre-determined amount of time before they make or break their connection. HVAC sequencers control multiple components and ensure they start or stop in the correct order to avoid overloading the system. Line voltage monitors measure the supply power to a component and turn it off if the power gets too low or too high.