Applications Using A Single−Stage Thermostat See figure 29 for ignition control sequence
B − Heating Sequence −− Control Thermostat Selection DIP Switch 1 ON in tage" Position
NOTE − In these applications, two−stage heat will be initi- ated by the integrated control if heating demand has not been satisfied after the field adjustable period (7 or 12 min- utes).
1 − On a call for heat, thermostat first−stage contacts close sending a signal to the integrated control. The inte- grated control runs a
2 − Once the control receives a signal that the low pres- sure switch has closed, the combustion air inducer be- gins a 15−second pre−purge in low speed.
NOTE − If the low fire pressure switch does not close the combustion air inducer will switch to high fire. After a 15 second pre−purge the high fire pressure switch will close and the unit will begin operation on high fire. After 10 to 20 seconds of high fire operation the unit will switch to low fire.
3 − After the pre−purge is complete, a 20−second initial ig- nitor warm−up period begins. The combustion air in- ducer continues to operate at low speed.
4 − After the 20−second warm−up period has ended, the gas valve is energized on low fire (first stage) and ignition oc- curs. At the same time, the control module sends a sig- nal to begin an indoor blower 30−second ON−delay. When the delay ends, the indoor blower motor is ener- gized on the low fire heating speed and the HUM con- tacts are energized. The integrated control also initi- ates a second−stage on delay (factory−set at 7 minutes; adjustable to 12 minutes).
5 − If the heating demand continues beyond the second− stage on delay, the integrated control energizes the combustion air inducer at high speed. The control also checks the high fire (second stage) pressure switch to make sure it is closed. The high fire (second stage) gas valve is energized and the indoor blower motor is energized for operation at the high fire heating speed.
6 − When the thermostat heating demand is satisfied, the combustion air inducer begins a 5−second low speed post−purge. The field−selected indoor blower off delay begins. The indoor blower operates at the low−fire heating speed.
7 − When the combustion air post−purge period is com- plete, the inducer, the HUM contacts as well as the 120V ACC terminals are de−energized. The indoor blower is de−energized at the end of the off delay.
HEATING OPERATION WITH TWO−STAGE THERMOSTAT
1 | 15 | 35 | 39 | 30* second 80 | 5 SEC | blower |
ON | Pre−Purge | Ignitor Warm−up | Trial For | blower | Post | delay |
OFF |
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1 stg heat demand |
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low speed CAI |
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ignitor |
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low fire gas valve |
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indoor blower low heat |
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| 2 stg heat demand |
| 30 seconds RECOGNITION PERIOD |
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| high speed CAI |
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| high fire gas valve |
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| indoor blower high heat |
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* Conventional thermostat 30 seconds, icomfort Touch® thermostat set for 30 adjustable 15 to 45 seconds.
FIGURE 28
HEATING OPERATION WITH SINGLE STAGE THERMOSTAT
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| blower |
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heat demand |
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low speed CAI |
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ignitor |
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low fire gas valve |
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indoor blower low heat |
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5 SEC
Post Purge
blower
delay
7 or 12 minutes after heating demand begins, furnace switches to high fire (depends on setting)
high speed CAI
high fire gas valve indoor blower high heat
* Conventional thermostat 30 seconds, icomfort Touch® thermostat set for 30 adjustable 15 to 45 seconds.
FIGURE 29
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