Lennox ALLIED Commercial TCA180S2B Standard Manual page 44

TCA180S, 180H, 210S, 240S SEQUENCE OF OPERATION
Power:
1. Line voltage from unit disconnect S48 or TB2 if equipped, energizes transformer T1. T1
provides 24VAC to the unit cooling, heating and blower controls and TB1 and TB14.
Blower Operation:
2. The main control module receives a demand from thermostat terminal G. A45 energizes
blower contactor K3 with 24VAC.
3. N.O. K3 closes, energizing blower B3.
Optional Power Exhaust Operation:
4. The economizer control module receives a demand and energizes exhaust fan relay K65 with
24VAC at 50% outside air damper open (adjustable).
5. N.O. K65−1 and N.O. K65−2 both close, energizing exhaust fan motors B10 and B11.
1st Stage Cooling (compressor B1)
6. First stage cooling demand Y1 and G is energized by the thermostat. G energizes blower.
7. 24VAC is routed from P113 on module A45 through N.C. freezestat S49, optional N.C. high
pressure switch S4 to energize compressor contactor K1.
8. N.O. contacts K1 close energizing compressor B1.
9. Optional N.O. low ambient switch S11 closes to energize condenser fan relay K10.
10. N.O. contacts K10−1 and K10−2 close energizing condenser fan B4 and B5.
2nd Stage Cooling (compressor B2 is energized)
11. Second stage cooling demand energizes Y2.
12. 24VAC is routed from P113 on module A45 through N.C. freezestat S50, optional N.C. high
pressure switch S7 to energize compressor contactor K2.
13. N.O. K2 closes energizing compressor B2.
14. Optional N.O. low ambient switch S84 closes to energize condenser fan relay K68.
15. .N.O. contacts K68−1 and K68−2 close energizing condenser fans B21 and B22.
3rd Stage Cooling (compressor B13 is energized)
16. Third stage cooling demand energizes Y3.
17. 24VAC is routed from P118 on module A45 through N.C. freezestat S53, optional N.C. high
pressure switch S28 to energize compressor contactor K14.
18. N.O. K14 closes energizing compressor B13.
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