Furnace Section Controls And Ignition System; Normal Furnace Operating Sequence - Rheem H2AC Installation Instructions Manual

FIGURE 18
34
VI. FURNACE SECTION CONTROLS AND
VI. IGNITION SYSTEM

NORMAL FURNACE OPERATING SEQUENCE

This unit is equipped with a two stage integrated direct spark ignition control.
NORMAL HEAT MODE
A. Call For First Stage (low fire) Only:
1. Zone thermostat contacts close, a call for first stage (low fire) heat is initiated.
2. Control runs self check.
3. Control checks the high-limit switch for normally closed contacts, each pressure
switch for normally open contacts, and all flame rollout switches for continuity.
4. Control energizes each low-fire inducer.
5. Control checks each low-fire pressure switch for closure.
6. If each low-fire pressure switch is closed, the control starts a 30 second prepurge.
If either low-fire pressure switch is still open after 180 seconds, the high-fire induc-
ers will be energized until closure.
7. After prepurge timeout, control initiates spark for 2 seconds minimum, 7 second
maximum ignition trial, initiates 45 second, second stage (high fire) warm up timing.
8. Control detects flame, de-energizes spark and initiates 45 second delay on blower
timing.
9. After a fixed 45 seconds indoor blower delay on, the control energizes the indoor
blower.
10. After the 45 second second stage warmup period control checks thermostat input.
If only W1 is called for, W2 is de-energized and the control starts a 5 second off
delay on the W2 inducer.
11. After fixed 5 seconds the W2 inducer is de-energized.
12. Control enters normal operating loop where all inputs are continuously checked.
B. Call For Second Stage, After First Stage Established; Starting from A.11:
1. If a call for second stage (high fire) is initiated after a call for first stage heat is
established, the control energizes the W2 inducer assures the high-fire pressure
switch is closed and energizes the second stage of the gas valve.
2. Control enters normal operating loop where all inputs are continuously checked.
C. Second Stage Satisfied; First Stage Still Called For; Starting From B.2:
1. Once the call for second stage is satisfied, the control starts a 30 second off delay
on W2 inducer and reduces the gas valve to first stage.
2. Control enters normal operating loop where all inputs are continuously checked.
D. First Stage Satisfied:
1. Zone thermostat is satisfied.
2. Control de-energizes gas valve.
3. Control senses loss of flame.
4. Control initiates 5 second inducer postpurge and 90 second indoor blower delay
off.
5. Control de-energizes inducer blower.
6. Control de-energizes indoor blower.
7. Control in the stand by mode with solid red LED.
ST-A1125-13