Lennox EL297DFV Series Unit Information page 38

Pressure Switch Check
To check pressure switch differential, refer to FIGURE 17
and use the provided fittings and tubing to follow the steps
below.
1 - Remove thermostat demand and allow unit to cycle
off.
2 - Remove the tubing from the negative side (red
and black or red) and positive side (black) of the
pressure switch (leave both connected to cold end
header box).
3 - Take the 2" length square tubing and connect to the
positive (+) side of the pressure switch. Take the 10"
length square tubing and tee into the tubing from
the positive side of the cold end header box and
the other side of the 2" square tubing. Connect the
other end of the 10" square tubing the positive (+)
side of the measuring device.
4 - Take a second piece the 2" length square tubing
and connect to the negative (-) side of the pressure
switch. Take a second piece of 10" length square
tubing and tee into the tubing from the negative (-)
side of the cold end header box and the other side
of the 2" square tubing. Connect the other end of
the 10" square tubing to the negative (-) side of the
measuring device.
Red and Black
or Red Tubing
(negative -)
PRESSURE SWITCH CHECK
Black Tubing
2" long Square
(positive +)
Tee
10" Long Square Tubing
Measuring Device
FIGURE 17
Page 38
5 - 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 at least 0.15"
greater than those listed in TABLE 15, TABLE 16
and TABLE 17. Readings in table are the set points
or "break points".
6 - Remove thermostat demand and allow to cycle off.
7 - Replace original pressure switch tubing.
NOTE - Pressure differential values (set point)
in table are the "break", or "open" specifications.
"Make", or "close" pressure differentials are 0.15"
greater than the set points listed in table
Tubing