Nortek YDHA - Page 33

Form O-Y P/N 273647R5, Page 33
Control Staged Gas
(2-stage, Option AG71
or 4-stage, Option
AG72 - applies to
Model YDSA only)
Sequence of Operation
1) W1 is energized and the DS1 control module veries that the pressure
switches are open.
2) Inducer (venter) is energized for pre-purge and the DS1 control module
veries that the low pressure switch is closed.
3) After the pre-purge period has elapsed (20 seconds), the DS1 control
module energizes the trial for ignition period (17 seconds).
4) After blower-on delay (30 seconds from ame detected), the
controller will energize the blower (supply fan).
5) If W2 is energized, the high gas output will energize.
6) After W1 and W2 are de-energized, the controller will run the blower-off
delay (120 seconds) and return to standby mode.
NOTE: For detailed information on the sequence of operation for the heat sections,
refer to section 3.5 Heating Staging Control, in the Model YDSA and YDHA Manual
for Space Temperature Control System Options D19 (form CP-Y-D19) or option
D21 (form CP-Y-D21).
Flue
Collection
Box
Venter
Assembly
Single Heat Section
Manifold Assembly with
2-Stage Option AG71
Optional
Low Gas
Pressure
Switch
Optional
High Gas
Pressure
Switch
2-Stg
Gas
Valve
Ignitor
Limit
Manifold Pressure Tap
Optional High Gas
Pressure Switch
Ignitor
Limit
Venter
Assembly
Dual Heat Section
Manifold Assembly
with 4-Stage
Option AG72
Manifold Pressure Tap
Heat Section 2
Manifold Pressure Tap
Heat Section 1
Venter
Assembly
2-Stg
Valve
Optional
High Gas
Pressure
Switch
2-Stg
Valve
Optional Low
Gas Pressure
Switch
Ignitor
Limit
FIGURE 24 - Furnaces with
Staged Control Option AG71
(2-stage control, single heat
section) and Option AG72
(4-stage control, dual heat
sections)
NOTE: Heat sections
illustrated are standard
efciency, non-condensing
furnaces. Controls for
condensing furnaces are the
same.
Staging Sequence -
Gas Control Option AG72
Heat
Section
2 1
Stage 1 off Low re
Stage 2 Low re Low re
Stage 3 Low re High re
Stage 4 High re High re
5.1 Gas Heat Controls (cont'd)