Lennox International Inc G61MP Circuit Breaker CB8, Control Box Control Transformer T1

I−UNIT COMPONENTS

G61MP unit components are shown in figure 1. The gas valve, combustion air inducer and burners can be ac- cessed by removing the burner access panel. Electrical components are in the control box (figure 2) found in the blower section.

G61MP units are factory equipped with a bottom return air panel in place. The panel is designed to be field removed as required for bottom air return. Markings are provided for side return air and may be cut out in the field.

ELECTROSTATIC DISCHARGE (ESD)

Precautions and Procedures

3. Circuit Breaker (CB8)

A 24V circuit breaker is also located in the control box. The switch provides overcurrent protection to the trans- former (T1). The breaker is rated 3A at 32V. If the current exceeds this limit the breaker will trip and all unit opera- tion will shutdown. The breaker can be manually reset by pressing the button on the face. See figure 3.

CIRCUIT BREAKER CB8

PRESS TO RESET

CAUTION

Electrostatic discharge can affect electronic components. Take precautions during furnace installation and service to protect the furnace’s electronic controls. Precautions will help to avoid control exposure to electrostatic dis- charge by putting the furnace, the control and the technician at the same electrostatic poten- tial. Neutralize electrostatic charge by touching hand and all tools on an unpainted unit surface, such as the gas valve or blower deck, before per- forming any service procedure.

A−Control Box

1. Control Transformer (T1)

A transformer located in the control box provides power to the low voltage section of the unit. Transformers on all models are rated 40VA with a 120V primary and a 24V sec- ondary.

2. Door Interlock Switch (S51)

A door interlock switch rated 14A at 125VAC is wired in se- ries with line voltage. When the blower door is removed the unit will shut down.

CONTROL BOX G61MP
	CIRCUIT
	BREAKER
DOOR INTERLOCK
SWITCH	TRANSFORMER
SURELIGHT
CONTROL
BOARD

FIGURE 2

FIGURE 3

WARNING

Shock hazard.

Disconnect power before servicing. Integrated Control Board is not field repairable. If control is inoperable, simply replace entire control.

Can cause injury or death. Unsafe operation will result if repair is attempted.

4. Integrated Control Board (A92)

All G61MP units are equipped with the Lennox Two−Stage Integrated control board. The system consists of a igni- tion control board (figure 4 with control terminal designa- tions in tables 3, 4 and 5) and ignitor (figure 7). The board and ignitor work in combination to ensure furnace ignition and ignitor durability. The board controls all major furnace operations. The board features two LED lights, DS1 and DS2 for troubleshooting. The board also has two accesso- ry terminals rated at (1) one amp. See table 6 for trouble- shooting diagnostic codes.

Electronic Ignition

At the beginning of the heat cycle, SureLight control moni- tors the first stage and second stage combustion air induc- er prove switch. The control will not begin the heating cycle if the first stage prove switch is closed (by−passed). Like- wise the control will not begin the second stage heating cycle if the second stage prove switch is closed, and will al- low first stage heat only. However if the second stage prove switch closes during the first stage pre−purge, the control will respond to second stage heat. Once the first stage prove switch is determined to be open, the combustion air inducer is energized on low (first stage) heat speed. When the differential in the prove switch is great enough, the prove switch closes and a 15−second pre−purge begins. If the switch is not proven within 2−1/2 minutes, the control goes into Watchguard−Pressure Switch mode for a 5−min- ute re−set period.

After the 15−second pre−purge period, the SureLight ignitor warms up for 20 seconds after which the gas valve opens for a 4−second trial for ignition. The ignitor energizes during the trial until flame is sensed. If ignition is not proved during the 4−second period, the control will try four more times with an inter purge and warm−up time between trials of 35 sec-

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