Lennox ML193DFE Series Unit Information page 15

Red and Black Tubing
or Red Tubing
(negative −)
To Cold End Header Box
1 - Remove thermostat demand and allow unit to cycle off.
2 - Install a tee in the negative (-) line (red and black tubing or
ning from the pressure switch to the cold end header box.
3 - Install a manometer with hose from the negative (-) side of
the manometer to the tee installed in the negative (-) line and
with hose from the positive (+) side of the manometer to the
tee in the positive (+) line.
NOTE -
ever the (+) port reads less negative pressure than the (-) port.
Measuring Pressure Differential
Field Provided Tubing
To Pressure Switch
"+" High
"−" Low
4 -
5 -
6 -
FIGURE 13
Page 15
Black Tubing
(positive +)
To Cold End Header Box
Operate unit and observe manometer reading.
Readings will change as heat exchanger warms.
a. Take one reading immediately after start up.
b. Take a second reading after unit has reached steady
state (approximately 5 minutes). This will be the pressure
differential.
The pressure differential should be greater
than those listed in table 7.
Remove thermostat demand and allow to cycle off.
Remove manometer and tee's. Reinstall combustion air
sensing hoses to the pressure switch.