Lennox ALLIED Commercial TCA180S2B Standard Manual page 46

TCA210H, 240H, 300S 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 main control module A45, P113 to N.C. freezestats S49, optional N.C.
high pressure switch S4. Compressor contactor K1 is energized.
8. N.O. contacts K1 closes 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 module A45 P113 to N.C. freezestat S50, optional N.C. high pressure
switch S7. Compressor contactor K2 is energized.
13. N.O. K2 closes energizing compressor B2.
14. Optional N.O. low ambient switch S84 closes. (S84 and S11 are wired in parallel)
3rd Stage Cooling (compressor B13 and B20 are energized)
15. Third stage cooling demand energizes Y3.
16. 24VAC is routed from main control module A45 , P118 to N.C. freezestats S53 and S95 then
continues through optional N.C. high pressure switches S28 and S96. Compressor contactors
K14 and K146 are energized.
17. N.O. K14 and K146 close energizing compressors B13 and B20.
18. Optional N.O. low ambient switches S28 and S96 (wired in parallel) close to energize condens-
er fan relay K68
19. N.O. contacts K68−1 and K68−2 close energizing fans B21 and B22.
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