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ZGB036, 048, 060, 074 P, Y, G, J & M Voltage Sequence of Operation
Power:
1. Line voltage from unit disconnect energizes transformer T1. T1 provides 24VAC power to the
unit cooling, heating and blower controls.
Blower Operation:
2. Indoor thermostat terminal G, via A3 ignition control, energizes blower contactor K3 with 24VAC.
3. N.O. K3 closes, energizing blower B3.
Economizer Operation:
nomizer modulates open (see table 14 in VII-ACCESSORIES section).
Power Exhaust Fan Operation:
5. The A6 economizer control module receives a Y1 thermostat demand and energizes exhaust fan
relay K65 with 24VAC at 50% outside air damper open (adjustable).
6. N.O. K65-1 closes, energizing exhaust fan motor B10.
Cooling Demand
7. First stage cooling demand Y1 and G is energized by the thermostat. G energizes blower.
8. 24VAC is routed through low voltage Y1 lead to optional N.C. compressor low discharge temperature
limit S3, N.C. high pressure switch S4 and N.C. compressor high temperature limit S5. Compressor
contactor K1 is energized.
9. N.O. K1-1 close energizing compressor B1 and outdoor fan B4.
First Stage Heat:
10. The thermostat initiates W1 heating demand.
11. 24VAC is routed to ignition control A3. A3 proves N.C. primary limit S10 and N.C. roll-out switch
S47.
12. Combustion air inducer blower B6 is energized.
13. After the combustion air inducer B6 has reached full speed, the combustion air proving switch
S18 contacts close.
14. After a 30 second delay A3 energizes the ignitor and gas valve GV1 on first stage.
Second Stage Heat:
15. Additional heating demand from the thermostat initiates W2.
16. A second stage heating demand is received by ignition control A3.
17. A3 energizes gas valve GV1 on second stage.
18. Relay K72-1 terminals 1 and 7 open, 7 and 4 close. K72-2 terminals 6 and 9 close and 9 and 3
open, energizing combustion air inducer B6 on high speed.
End of Second Stage Heat:
19. Heating demand is satisfied. W2 (second stage) is de-energized.
20. Second stage heat is de-energized on GV1 by ignition control A3.
bustion air inducer B6 is now on low speed.
End of First Stage Heat:
22. Heating demand is satisfied. W1 (first stage) is de-energized.
23. Ignition A3 is de-energized in turn de-energizing gas valve GV1 and combustion air inducer B6.
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