Is energized and the flame rectification circuit

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is energized and the flame rectification circuit looks for the presence of flame, line 12. If flame is sensed, the gas valve remains energized and the igniter is de-energized. The heating fan relay coil (HFR line 17) is energized after a delay of two to three minutes. The normally open HFR contacts close to energize the heating fan speed and the normally closed HFR contacts open to prevent operation of the cooling fan speed, lines 5 and 6. Starting of the indoor fan motor is delayed to allow the furnace time to heat up.
39-23) List the operational sequence for the second stage of Figure 39-34. Just list what happens when the W2 terminal is energized.
130 the coil to the second heat sequencer HS2, lines 1 and 2. HS2 closes its contacts after a time delay to energize the second heater HTR2, line 3. Note that HS1 and HS2 normally open contacts in parallel with the IFR contacts, lines 10 and 12. They insure that the indoor fan motor will operate whenever the heat strips are operating.
UNIT 40 REVIEW QUESTIONS ANSWER KEY 40-1) What is a communicating control system?
40-2) Explain the difference between the way a relay logic control system operates and the way a communicating control system operates.
40-3) How can a two stage heat pump be controlled by only four wires?
40-4) What is a communicating protocol?
40-5) List two open protocols.
40-6) What are the four wires used in a common four-wire communicating system?
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