Lennox SLP99UHV Series

Page 42
Vent Calibration
The vent calibration sequence establishes furnace oper-
ating parameters in a specic installation. The integrat-
ed control runs the calibration and may be repeated as
necessary to maintain proper furnace operation. Prior to
calibration, all duct work (and returns) vent pipe and con-
densate trap (primed) must be connected.
If calibration is successful the data is stored in memory
and will be used to determine furnace operation and main-
tain parameters during heat call. If calibration is not suc-
cessful, the integrated control will proceed to a 5 minute
delay and signal the appropriate code. After the 5 minute
delay the calibration will be repeated 4 more times with a
5 minute delay in between. If still unsuccessful after the
4 trials (total 5) the integrated control will go into a 1 hour
soft lockout.
Calibration may be initiated by:
• Initial call for heat
• Cycling main power o󰀨 / on and then call for heat
• Venting conditions change (a󰀨ecting high and low
pressure switch operation)
• Ramp down low re switch check failed (calibration
will follow next call for heat)
• The service technician (by pressing the push but-
ton found on the integrated control until the control
cycles through to “Field Test Mode”)
The integrated control will do the following during calibra-
tion:
1 - Verify both low pressure switch and high pressure
switch are open. If either are closed log error and
end calibration.
2 - Start inducer at a predetermined low RPM (1600).
Wait 7.5 seconds.
3 - Check low pressure switch, if open, increase RPM
by 250, wait 5 seconds. Repeat this step until low
pressure switch is closed.
4 - Decrease RPM by 50, wait 5 seconds and look for
the low pressure switch to open. Repeat this step
until it is open.
5 - Keep this RPM as RPM1.
6 - Increase RPM by 1250. Wait 5 seconds.
7 - Check high pressure switch, if open, increase RPM
by 250, wait 5 seconds. Repeat this step until high
pressure switch is closed.
8 - Decrease RPM by 50, check after 5 seconds.
Repeat this step until switch is open.
9 - Keep this RPM as RPM2.
10 - Calibration complete.
NOTE - If after a successful calibration and a heat call is
present the integrated control will by-pass the prepurge
state and go straight into ignitor warm up
After calibration, the integrated control stores the RPM1
and RPM2 values. The low re (35%) and high re (100%)
RPM points are calculated by adding margin values to the
RPM1 and RPM2 values.
The integrated control also initiates a low re switch check
at the end of a normal heating cycle described below. If
this check fails the pressure switch calibration will follow
on the next call for heat.
1 - The inducer runs 15 seconds at the last ring rate
before the heat call ended.
2 - Inducer runs at 35% ring rate RPM (RPM1 + low
pressure switch open RPM margin value).
3 - If low pressure switch is open, set ag for calibration
on next call for heat. Turn inducer o󰀨 until next call
for heat.
4 - If low pressure switch is closed move inducer speed
to RPM1. Allow 5 seconds for stabilization.
5 - If low pressure switch opens turn o󰀨 inducer. No
further action.
6 - If low pressure switch is still closed, decrease
inducer speed 1/2 of the low pressure switch open
RPM margin. Allow 5 seconds to stabilize.
7 - If low pressure switch is open turn o󰀨 inducer. No
further action.
8 - If low pressure switch is still closed, set ag for
calibration on next call for heat and turn o󰀨 inducer.
Measuring pressure di󰀨erential (FIGURE 18)
Checks of pressure di󰀨erential can aid in troubleshooting.
Lennox provides a kit (10L34) if necessary. When measur-
ing the pressure di󰀨erential, readings should be taken at
the pressure switch. Lack of di󰀨erential usually indicates
problems in the intake or exhaust piping, but may indicate
problems in the heat exchanger, condensing coil, header
boxes, combustion inducer or other components.
The di󰀨erential pressure is the di󰀨erence in pressure
measured across the cold end header box orice.