CSLB C-20 HVAC ContractorControls, Electrical and SafetyEasy
A technician is calibrating a mechanical thermostat with an adjustable heat anticipator. The furnace's primary gas valve control circuit draws 0.4 amp. Where should the heat anticipator pointer be set?
- AAt the lowest scale setting to maximize cycle length
- BAt 0.4 amp, matching the control circuit's actual current draw
- CAt 1.0 amp regardless of the equipment
- DAt the highest scale setting to prevent short cycling
Show answer & explanationAnswer & explanation
Correct answer: B. At 0.4 amp, matching the control circuit's actual current draw
The heat anticipator must be set to match the actual current draw of the primary control circuit (measured with an ammeter or read from the gas valve/relay nameplate) so that the thermostat cycles the burner at the correct temperature swing. Setting it too high or too low causes short cycling or excessive temperature overshoot.
Why the other options are wrong
- A. An incorrectly low setting causes rapid short cycling.
- C. An arbitrary fixed value ignores the specific equipment's actual draw.
- D. An incorrectly high setting causes long overshoot before shutoff.
Heat Anticipator Setting
A small adjustable resistor inside a mechanical thermostat that must be set to the actual amperage of the heating control circuit to properly time the thermostat's cycling.
- Measured with a clamp-on ammeter in series with the control circuit
- Setting too high causes overshoot; too low causes short cycling
- Not used on electronic/digital thermostats
Memory trick: Match the amp, avoid the cramp (short cycling).