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Start-Up & Operation Information
 WARNING
If you do not follow these instructions exactly, a re 
or explosion may result causing property damage, 
personal injury or death.
BEFORE PLACING THE UNIT INTO OPERATION, smell
all  around  the  appliance  area  for  gas.  Be  sure  to  smell 
next to the oor because some gas is heavier than air and 
will settle on the oor.
The  gas  valve  on  the  SLP99DF  is  equipped  with  a  gas 
control  switch.  Use  only  your  hand  to  move  the  control 
switch.  Never  use  tools.  If  the  switch  will  not  move  by 
hand, do not try to repair  it.  Call a licensed professional 
service technician (or equivalent). Force or attempted re-
pair may result in a re or explosion.
Placing the SLP99DF furnace into operation:
SLP99DF  units  are  equipped  with  a  SureLight
®
 ign tion 
system. Do not attempt to manually light burners on this 
furnace. Each time the thermostat calls for heat, the burn-
ers  will  automatically  light.  The  ignitor  does  not  get  hot 
when there is no call for heat on units with SureLight®
ignition system.
Operating the Gas Valve (Figure 2)
1 -    STOP! Read the safety information at the beginning 
of this section.
2 -  Set the thermostat to the lowest setting.
3 -  Turn o all electrical power to the unit.
4 -   This furnace is equipped with an ignition device 
which automatically lights the burners. Do not try to 
light the burners by hand.
5 -  Remove the outer access panel.
6 -   Move  the  gas  valve  switch  to  the  OFF position 
gure 2.
7 -    Wait ve minutes to clear out any gas. If you then 
smell gas, STOP! Immediately call your gas supplier 
from  neighbor’s  phone.  Follow  the  gas  supplier’s 
instructions. If you do not smell gas go to next step.
NEGATIVE AIR
PRESSURE PORT
POSITIVE AIR
PRESSURE PORT
MANIFOLD
PRESSURE TAP
INLET
OUTLET
SUPPLY
PRESSURE
TAP
GAS VALVE SHOWN IN THE ON POSITION
FIGURE 2 
8 -   Move gas valve switch to ON position. See gure 2.
9 -  Replace the outer access panel.
10 - Tur n on all electrical power to to the unit
11 - Se t the thermostat to desired setting.
NOTE - When unit is initially started, steps 1 through 
11 may need to be repeated to purge air from gas line.
12 -   If the appliance will not operate, follow the section 
“Turning O Gas to the Unit” and call your service 
technician or gas supplier. 
Turning O Gas to the Unit 
 WARNING
If overheating occurs or if gas supply fails to shut 
o,  shut  o  the  manual  gas  valve  to  the  furnace 
before shutting o electrical supply.
1 -   Set the th ermostat to the lowest setting.
2 -   Turn o all electrical power to the unit if service is to 
be performed.
3 -   Remove the outer access panel.
4 -   Move the gas valve switch to the OFF position.
5 -   Replace the outer access panel.
 CAUTION
Do not set thermostat below 60F (16C) in heating 
mode. Setting below 60F (16C) reduces the number 
of heating cycles. Damage to the unit may occur that 
is not covered by the warranty.
Filters
All SLP99DF lters are installed external to the unit. Filters 
should be inspected monthly. Clean or replace the lter(s) 
when necessary to ensure proper furnace operation. A l-
ter must be in place when the unit is operating. See 
table 1 for recommended lter sizes.
NOTE - Use  replacement  lters  that  are  similar  in  size 
and eciency  ratings  to those  originally provided  by the 
installing contractor. Use of replacement lters with higher 
ltration ratings may restrict air ow to the  furnace.  This 
may result in reduced unit eciency, as well as premature 
blower motor failure.
The lter access panel must also be in place and properly
secured during unit operation.
TABLE 1
Furnace 
Cabinet Width
Filter Size
Side Return Bottom Return
17-1/2” 16 x 25 x 1 (1) 16 x 25 x 1 (1)
21-1/2” 16 x 25 x 1 (1) 16 x 25 x 1 (1)