HVAC Procedure and Performance Guide

TASK: Analyze electronic circuit containing power source, control card, sensor and control device


Defective components in solid-state electronic circuit must be identified and required repairs determined.  Applicable safety procedures must be followed.


  1. Review job order, manufacturer’s specifications, wiring diagrams and troubleshooting procedures.
  2. Determine the following:

a. Function(s) performed by circuit

b. Power supply voltage

c. Sensor type

1) Switch (bimetal, filled system)

2) AC/DC rectification (flame rectifier)

3) Variable resistance (thermistor, CAD cell)

4) Millivolt generation (thermocouple, thermopile)

d. Control device type

1)  Switch

2) Relay

3) Control valve

4) Safety device

e. Board-mounted relay information

1)  Coil voltage

2) Contact rating

3) Time-delay capabilities

f. Devices bearing Underwriter’s Laboratory or other testing agency labels