Lennox SLP99DFV Series User Manual

Page 57
Furnace should operate at least 5 minutes before check-
ing gas ow. Determine time in seconds for two revolu-
tions of gas through the meter. (Two revolutions assures
a more accurate time.) Divide by two and compare to time
in TABLE 28. If manifold pressure matches TABLE 33 and
rate is incorrect, check gas orices for proper size and
restriction. Remove temporary gas meter if installed.
E-Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to
supply pressure tap on the gas valve. See FIGURE 47.
Check gas line pressure with unit ring at maximum rate.
Low pressure may result in erratic operation or underre.
High pressure can result in permanent damage to gas
valve or overre. See TABLE 29 for operating pressure at
unit gas connection (line).
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres-
sure must fall within range listed in TABLE 29.
TABLE 29
All Units Natural LP/Propane
Line Pressure WC” 4.5 - 10.5
11.0 - 13.0
Manifold Pressure Measurement (FIGURE 49)
To correctly measure manifold pressure, the di󰀨erential
pressure between the positive gas manifold and the neg-
ative burner box must be considered. Use pressure test
adapter kit (available as Lennox part 10L34) to assist in
measurement.
1 - Remove the threaded plug from the outlet side of
the gas valve and install a eld-provided barbed
tting. Connect measuring device “+” connection to
barbed tting to measure manifold pressure.
2 - Tee into the gas valve regulator vent hose and
connect measuring device “-” connection.
3 - Start unit on low heat (35% rate) and allow 5 minutes
for unit to reach steady state.
4 - While waiting for the unit to stabilize, notice the
ame. Flame should be stable and should not lift
from burner. Natural gas should burn blue.
5 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
TABLE 33.
6 - Repeat steps 3, 4 and 5 on high heat.
7 - Shut unit o󰀨 and remove manometer as soon as
an accurate reading has been obtained. Take care
to remove barbed tting and replace threaded plug.
8 - Start unit and perform leak check. Seal leaks if
found.
Operating Pressure Signal (Delta P) Measurement
(FIGURE 50)
Operating pressure signal can be taken while the manifold
pressure pressure check is taken (using two measuring
devices). Or, taken after the manifold pressure measure-
ment is complete.
1 - Tee into the negative line between the gas valve and
pressure switch and connect to measuring device
negative “-”.
2 - Tee into the positive line between the gas valve and
pressure switch and connect to measuring device
positive “+”.
3 - Start unit on low heat (35% rate) and allow 5 minutes
for unit to reach steady state.
4 - After allowing unit to stabilize for 5 minutes, record
operating pressure signal and compare to value
given in TABLE 33.
5 - Repeat steps 3 on 4 high heat.
CAUTION
Do not attempt to make adjustments to the gas
valve.

Lennox SLP99DFV Series Specifications

General

Brand	Lennox
Model	SLP99DFV Series
Category	Furnace
Language	English