Lennox International Inc G61MP specifications Clamshell Heat Exchanger, Flame Rollout Switches S47

6. Clamshell Heat Exchanger

G61MP units use an aluminized steel primary and stain- less steel secondary heat exchanger assembly. Heat is transferred to the air stream from all surfaces of the heat exchanger. The shape of the heat exchanger ensures maximum efficiency.

The combustion air inducer pulls fresh air through the air intake box. This air is mixed with gas in the burner venturi and at the corbel orifices. The gas / air mixture is then burned at the entrance of each clamshell. Combustion gases are then pulled through the primary and secondary heat exchangers and exhausted out the exhaust vent pipe.

7. Flame Rollout Switches (S47)

Flame rollout switch S47 is a high temperature limit located on each side of the burner box. Each furnace is equipped with two identical switches. The limit is a N.C. SPST manu- al-reset limit connected in series with the primary limit S10. When S47 senses rollout, the circuit breaks and the ignition control immediately stops ignition and closes the gas valve.

If unit is running and flame rollout is detected, the gas valve will close and ignition control will be disabled. Rollout can be caused by a blocked heat exchanger, flue or lack of combustion air. The switch is factory set to trip (open) at 250°F and cannot be adjusted. The switch can be manually reset. To manually reset a tripped switch, push the reset but- ton located on the control.

8. Primary Limit Control (S10)

Figure 8 shows the primary limit (S10) used on G61MP units located in the heating vestibule panel. S10 is provided with a shield on some models (figure 8) and must not be removed. Note orientation of shield and limit if limit is replaced. When ex- cess heat is sensed in the heat exchanger, the limit will open. Once the limit opens, the furnace control energizes the supply air blower and de−energizes the gas valve. The limit automatically resets when unit temperature returns to nor- mal. The switch is factory set and cannot be adjusted.

9.Backup Secondary Limit Control (S113) (G61MP−090, 110, 135 only)

Backup secondary limit control S113 is a N.C. auto−reset switch located on the combustion air inducer. S113 acts as a backup to primary limit S10 in the event of an indoor blow- er failure. S113 contacts open when temperature on the CAI reaches 142°.

10. Gas Valve (GV1)

The G61MP uses a two−stage gas valve manufactured by Honeywell (figure 35) or White Rodgers (figure 36). The valves are internally redundant to assure safety shut−off. If the gas valve must be replaced, the same type valve must be used.

24VAC terminals and gas control knob or switch are located on the valve. All terminals on the gas valve are connected to wires from the electronic ignition control. 24V applied to the ter- minals energizes the valve.

Inlet and outlet pressure taps are located on the valve. A regu- lator adjustment screw is located on the valve.

LPG change over kit s are available from Lennox. Kits include burner orifices and a gas valve regulator conversion kit.

The burner box is sealed and operates under a negative pressure. A pressure hose is connected from the burner box to the gas valve. The gas valve senses the pressure in the burner box and changes gas valve outlet (manifold) pressure based on changes in the burner box pressure. The intent is to compensate for different vent configura- tions which can greatly affect the rate of the unit.

PRIMARY LIMIT LOCATION

limit shield

090, −110 and

−135 only

limit faces shield

FIGURE 8

11.Combustion Air Inducer Prove Switch (S18)

All G61MP units are equipped with combustion air prove switches located on the combustion air inducer housing. G61MP−045 and −070 (figure 10) units have two combustion air proving switches. G61MP−090, −110 and −135 units are equipped with two dual prove switch semblies" consist- ing of two switches acting as one. See figure 9. The switches are connected to the cold end header box by means of a flexible hose that monitors negative air pressure in the cold end header box.

The switches are a single-pole single-throw proving switch electrically connected to the furnace control. The purpose of the switch is to prevent burner operation if the combustion air inducer is not operating or if the flue becomes obstructed.

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