Single Stage Multi Position Furnace
Service Manual
7
440 08 2001 02
7. BURNERS
Burners used in this series of furnace are of the “INSHOT”
type. Their operation can be compared to that of a torch in
that they produce a hard, sharp, somewhat noisy flame.
Noise should not be an issue, however, because of the
closed compartment design. In order to insure that the burn-
ers are operating properly, and at their design noise level,
proper adjustment of the gas (manifold) pressure is essen-
tial. See page 6 for further information on manifold pressure
adjustments.
The burners used in this series ARE NOT EQUIPPED WITH
AIR SHUTTERS, as none are required. Proper operation
(flame characteristics) is obtained by insuring that the orifice
size, and manifold pressure are correct for the fuel being
used and the altitude of the installation.
Main Burner
Burner Face
10--10--78
Figure 6
8. L.P. PRESSURE SWITCH
Models converted to operate on L.P. Gas will be installed
with an L.P. Pressure Switch. If so equipped, the switch will
be located in the gas supply line (in a “Tee” fitting), just ahead
of the gas valve.
The purpose of this switch is to prevent furnace operating un-
der low line (Supply) pressure conditions. Operating under
low line pressure conditions, can create problems such as in-
complete combustion, flashback, sooting, etc.
The switch is a “Normally Open” pressure operated switch
that is wired in series with the furnace (vent) pressure switch.
The L.P. Pressure Switch closes when line (Supply) pres-
sure is 8.0
²
W.C. or higher. the L.P. Pressure Switch Opens
if line pressure falls below 6.0
²
+ 0.6
²
W.C. interrupting
power to the gas valve.
On some models, it is located (electrically) between the Fur-
nace (vent) pressure switch and the gas Valve.
Typical L.P. Pressure Switch
Figure 7
9. HIGH ALTITUDE OPERATION
These furnaces are designed to operate in the majority of the
country without modifications. At altitudes over 2,000
¢
above
sea level, however, certain measures need to be taken to in-
sure continued, safe reliable operation. For example, units
must be de--rated for altitude (by adjusting manifold pres-
sure and/or changing orifice size) based upon the type of fuel
(I.E. Natural Gas or L.P. gas), Btu content of the gas, and
installed altitude.
ALL UNITS must have a high altitude pressure switch
installed at altitudes above 4,000
¢
above sea level.
When servicing a unit installed at altitudes above 2,000
¢
in-
sure that it has been properly modified to operate at that alti-
tude. See the sections on Gas pressure (Page *), and pres-
sure switches (Page **) to obtain specific information for you
particular installation altitude.
