Single Stage Multi Position Furnace
Service
Manual
5
440 08 2001 02
5. INTERLOCK SWITCH
The blower compartment door of all models is equipped with
an interlock switch. This switch is “Normally Open” (closes
when the door is on the furnace) and interrupts furnace op-
eration when the door is open. This interlock switch is a safe-
ty device, and SHOULD NEVER BE BY--PASSED.
Since this is a single pole switch, (breaking only one side of
the line) proper line voltage is essential to insure that furnace
components are not “HOT” when switch is open. (See
Checking Grounding and Polarity)
Figure 3
Typ ical Interlock Switch
10--12--96
6. GAS SUPPLY
Typical Gas Valve HoneywellFigure 4
dwg 25--23--31a
INLET
Manifold Pressure
Adjustment
Pilot P ressure
Adjustment (Hid-
den)
On\Off
Switch
Diagnostic Light
OUTLET
An adequately sized gas supply to the furnace is required for
proper operation. Gas piping which is undersized will not
provide sufficient capacity for proper operation. Piping
should be sized in accordance with accepted industry stan-
dards.
NATURAL GAS
Inlet (Supply) pressure to the furnace should be checked (at
the gas valve) with ALL OTHER GAS FIRED APPLIANCES
OPERATING. Inlet (Supply) pressure to the furnace under
these conditions MUST be a minimum of 4.5² W.C. (Water
Column). If the inlet pressure is less, it may be an indication
of undersized piping or regulator problems.
L.P. GAS
Inlet (Supply) pressure to the furnace should be checked in
the same manner as for Natural Gas, however with L.P. Gas,
the inlet pressure MUST be a minimum of 11² W.C. If this
cannot be obtained, problems are indicated in either the reg-
ulator or pipe sizing.
Table 1 Gas Pressures Below 2000¢
¢¢
¢
Gas
Supply Pressure
Manifold
Type
Recommended Max. Min.
Pressure
Natural 7² 14² 4.5² 3.5²
LP 11² 14² 11² 10²
Important Note:
· With Propane gas, the rated input is obtained when the
BTU content is 2,500 BTU per cubic foot and manifold
pressure set at 10²
²²
² W.C.
· If Propane gas has a different BTU content, orifices
MUST be changed by licensed Propane installer.
· Measured input can NOT exceed rated input.
· Any major change in gas flow requires changing burner
orifice size.
CHECKING INPUT (FIRING) RATE
Once it has been determined that the gas supply is correct
to the furnace, it is necessary to check the input (firing) rate,
This can be done in two (2) ways. First by checking and ad-
justing (as necessary) the manifold (Outlet) pressure. The
second way is to “Clock” the gas meter.
Fire or explosion hazard.
Turn OFF gas at shut off before connecting
manometer .
Failure to turn OFF gas at shut off before
connecting manometer can result in death,
personal injury and/or property damage.
!
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