ICP 9MPT Service Manual

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Two- Stage Multi Position Furnace Service Manual7440 08 2002 027. L.P. PRESSURE SWITCHModels converted to operate on L.P. Gas will be installedwith an L.P. Pressure Switch. The switch will be located in thegas supply line (in a ìTeeî 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 underlow line pressure conditions, can create problems such as in-complete combustion, flashback, sooting, etc.The switch is a ìNormally Openî pressure operated switchthat is wired in series with the furnace (Lo--fire) pressureswitch. The L.P. Pressure Switch closes when line (Supply)pressure is 8.0² W.C. or higher. the L.P. Pressure SwitchOpens if line pressure falls below 6.0² + 0.6² W.C. interrupt-ing power to the gas valve.It is located (electrically) between the Main Limit Switch andthe furnace (vent) pressure switch. The switcht is located(electrically) between the Furnace (Lo--fire) pressure switchand the gas Valve.Typical L.P. Pressure SwitchFigure 68. HIGH ALTITUDE OPERATIONThese furnaces are designed to operate in the majority of thecountry without modifications. At altitudes over 2,000¢ abovesea level, however, certain measures need to be taken to in-sure continued, safe reliable operation. For example, unitsmust 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, andinstalled altitude.ALL UNITS must have a high altitude pressure switchinstalled 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, and pressureswitches to obtain specific information for you particularinstallation altitude.9. BURNERSBurners used in this series of furnace are of the ìINSHOTîtype. Their operation can be compared to that of a torch inthat they produce a hard, sharp, somewhat noisy flame.Noise should not be an issue, however, because of theclosed burner box design. In order to insure that the burnersare operating properly, and at their design noise level, properadjustment of the gas (manifold) pressure is essential. Forfurther information on manifold pressure adjustments checkthe section on ìGas Supplyî.The burners used in this series ARE NOT EQUIPPED WITHAIR SHUTTERS, as none are required. Proper operation(flame characteristics) is obtained by insuring that the orificesize, and manifold pressure are correct for the fuel beingused and the altitude of the installation.Main BurnerBurner Face10--10--78Figure 7