Carrier 48GC04 Service And Maintenance Instructions

28Fuel Types and PressuresNATURAL GASThe 48GC unit is factory-equipped for use with natural gas(NG) fuel at elevation under 2000 ft (610 m). See section “Ori-fice Replacement” for information in modifying this unit forinstallation at elevations above 2000 ft (610 m).Gas line pressure entering the unit’s main gas valve must bewithin specified ranges (see Table 7). Adjust unit gas regulatorvalve as required or consult local gas utility.Manifold pressure is factory-adjusted for NG fuel use. Adjustas required to obtain best flame characteristic. (See Table 8.)LIQUID PROPANEAccessory packages are available for field-installation that willconvert the 48GC unit (except low NOx model) to operate withliquid propane (LP) fuels. These kits include new orifice spuds,new springs for gas valves and a supply line low pressureswitch. See High Altitude Gas Conversion Kit Gas Heat-ing/Electric Cooling 3 to 15 Ton Small Rooftop Units Accesso-ry LP (Liquid Propane) Installation Instructions for details onorifice size selections.Fuel line pressure entering unit gas valve must remain withinspecified range. (See Table 9.)Manifold pressure for LP fuel use must be adjusted to specifiedrange (see Table 10). Follow instructions in the accessory kit tomake initial readjustment.SUPPLY PRESSURE SWITCHThe LP conversion kit includes a supply low pressure switch.The switch contacts (from terminal C to terminal NO) willopen the gas valve power whenever the supply line pressuredrops below the set point. See Fig. 48 and 49. If the lowpressure remains open for 15 minutes during a call for heat, theIGC circuit will initiate a Ignition Fault (5 flashes) lockout. Re-set of the low pressure switch is automatic on rise in supplyline pressure. Reset of the IGC requires a recycle of unit powerafter the low pressure switch has closed.Fig. 48 — LP Low Pressure Switch (Installed)Fig. 49 — LP Supply Line Low PressureSwitch WiringThis switch also prevents operation when the propane tank lev-el is low, which can result in gas with a high concentration ofimpurities, additives, and residues that have settled to the bot-tom of the tank. Operation under these conditions can causeharm to the heat exchanger system. Contact your fuel supplierif this condition is suspected.Flue Gas PassagewaysTo inspect the flue collector box and upper areas of the heat ex-changer:1. Remove the combustion blower wheel and motor assem-bly according to directions in Combustion-Air Blower sec-tion. See Fig. 50.2. Remove the flue cover to inspect the heat exchanger.3. Clean all surfaces as required using a wire brush.Combustion-Air BlowerClean periodically to assure proper airflow and heating effi-ciency. Inspect blower wheel every fall and periodically duringheating season. For the first heating season, inspect blowerwheel every two months to determine proper cleaning frequency.To access burner section, slide the burner partition panel out ofthe unit.Table 7 — Natural Gas Supply Line Pressure RangesUNIT MODEL UNIT SIZE MIN MAX48GCD/E/S/R 04, 05, 06 4.0 in. wg(996 Pa)13.0 in. wg(3240 Pa)48GCF/T(High Heat Units Only) 05, 06 5.0 in. wg(1245 Pa)13.0 in. wg(3240 Pa)Table 8 — Natural Gas Manifold Pressure RangesUNIT MODEL UNIT SIZE HIGH FIRE LOW FIRE48GCD/E/S/R 04, 05, 06 3.5 in. wg(872 Pa)1.7 in. wg(423 Pa)48GCF/T(High Heat Units Only) 05, 06 3.5 in. wg(872 Pa)1.7 in. wg(423 Pa)IMPORTANT: Low NOx models include specially-sizedorifices and use of different flue flow limits and tube baf-fles. Because of these extra features, conversion of thesemodels to LP is not recommended.Table 9 — Liquid Propane Supply Line PressureRangesUNIT MODEL UNIT SIZE MIN MAX48GCD/E/S/R 04, 05, 06 11.0 in. wg(2740 Pa)13.0 in. wg(3240 Pa)48GCF/T(High Heat Units Only) 05, 06 11.0 in. wg(2740 Pa) 13.0 in. wg(3240 Pa)Table 10 — Liquid Propane Manifold PressureRangesUNIT MODEL UNIT SIZE MIN MAX48GCD/E/S/R 04, 05, 06 10 in. wg(2490 Pa)5 in. wg(1245 Pa)48GCF/T(High Heat Units Only) 05, 06 10 in. wg(2490 Pa)5 in. wg(1245 Pa)PNKW2TSTATGRABRNIGCJ2-12IGCJ2-11BRNC NOMGV CLP LPS