HVAC Electrical Switches, Part 2:
Electromechanical Time Delay Switches

  • Author: AC Service Tech
  • Level: Intermediate
  • Study time: < 1 Hour
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Electromechanical time delay switches, such as sequencers, are used in HVAC units such as air handlers to control when the blower motor or electric strip heaters are turned on.

They may also be found in some older gas furnaces, such as garage heaters. It is important to understand how and why these are used in units.

Learn their basic operation and how to test these switches safely when not under high current loads.

Most switches can be tested by measuring electrical resistance while the power is off or while only 24V is present.

Craig Migliaccio - AC Service Tech

“People often confuse sequencers with normal relays but its important to know how these function in order to test and install them in an effective manner!”
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