Residential HVAC Controls) Electronic Timers

 

1. Introduction to Electronic Timers

• Definition: Electronic timers in HVAC systems are programmed to turn components on or off at specific times.
• Benefits: Increase energy efficiency by operating equipment only during periods of occupancy.
• Control Relay: Helpful to delay the operation of contacts as they open or close when voltage is applied or removed from the coil.

2. Time Delay Relays

• Function: Allow for delayed operation of HVAC components.
• Fan Delay (Delay on Break):
  • Fixed Time Device or Adjustable: Can have fixed timing or multiple timing ranges and functions.
  • Integration: May be integrated into the electronic control board or be a standalone device.
  • Adjustment: Integrated components can be field-adjusted to shorten or lengthen delay duration.
  • Use in HVAC Systems: Delays the starting of the blower until the heat exchanger is heated and operates the blower after the compressor or heating cycle shuts down.

3. Compressor Delay Timers

• Purpose: Prevent short cycling of the compressor, reducing wear and tear.
• Operation: Once the compressor shuts down, it cannot be restarted for a specified time.
• Integration: Often built into the electronic space thermostat.

4. Electronic Compressor Controls

• Staging Strategy:
  • Definition: Process of identifying predetermined conditions and programming the system to respond.
  • Application: Used in multiple compressor systems to manage system load.
  • Function: Prevents multiple compressors from starting simultaneously.
• Control Board Requirements:
  • Inputs and Outputs: Ensure correct inputs produce correct outputs, indicating proper functioning.
  • Monitoring: Control board monitors safety devices and control inputs for safe, reliable operation.
  • Service Manual: Technicians should refer to the service manual for specific controls to ensure inputs and outputs are within the recommended range.