Lennox ML193UH045P36B Unit Information page 16

4. Primary Limit Control (Figure 12)
Primary limit (S10) used on ML193UH units is located in the
heating vestibule panel. When excess 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 normal. The switch is fac­
tory set and cannot be adjusted. For limit replacement re­
move wires from limit terminals, remove mounting screws,
rotate limit switch 90 degrees and slowly remove from the
vestibule panel. Install replacement limit with same care.
Primary Limit Location and Heat Exchanger
Install limit face down
FIGURE 12
5. Heat Exchanger (Figure 12)
ML193UH 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 burn­
er box. This air is mixed with gas in the burners. The gas /
air mixture is then burned at the entrance of each clam­
shell. Combustion gases are then pulled through the pri­
mary and secondary heat exchangers and exhausted out
the exhaust vent pipe.
6. Burners (Figure 13)
All units use inshot burners. Burners are factory set and do
not require adjustment. Burners can be removed as an as­
sembly for service. Burner maintenance and service is de­
tailed in the MAINTENANCE section of this manual. Each
burner uses an orifice which is precisely matched to the
burner input. See table 8 for orifice size. The burner is sup­
ported by the orifice and will easily slide off for service. A
flame retention ring in the end of each burner maintains
correct flame length and shape and keeps the flame from
lifting off the burner head.
Unit
All
All
Burner Detail Top View
FLAME SENSOR
7. Gas Valve (GV1)
The ML193UH uses an internally redundant valve to as­
sure safety shut‐off. If the gas valve must be replaced, the
same type valve must be used.
24VAC terminals and gas control switch are located on top
of the valve. All terminals on the gas valve are connected to
wires from the ignition control. 24V applied to the terminals
opens the valve.
Inlet and outlet pressure taps are located on the valve. A
manifold adjustment screw is also located on the valve. An
LPG changeover kit is available.
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
INLET
PRESSURE
PORT
Page 16
TABLE 8
Gas Orifice Size
Fuel Orifice Size
Natural 0.0625
L.P./Propane 0.0340
IGNITOR
ORIFICES
FIGURE 13
Gas Valve
MANIFOLD
PRESSURE
OUTLET
FIGURE 14
PORT