Carrier 58DXT Operating Instructions Manual

Also see for 58DXT: User's information manual Service and maintenance instructions

Contents

Carrier 58DXT Operating Instructions Manual Manual pdf 15 page image

circuit, the furnace blower motor BLWM continuesoperating on heating speed for an additional 90 sec.(4.) Opening R-Y2 circuit reduces blower motor BLWMspeed to heat pump low-heat speed.6. Defrosta. When furnace control R to W/W1-and-Y/Y2 circuits areclosed, furnace control CPU continues blower motorBLWM operation at heat pump heating speed until end ofprepurge period, then shuts off until end of HSI ignitor onperiod (22 sec).b. When installed with a heat pump, furnace control CPUautomatically holds blower off time to 22 sec during HSIignitor on period. After 17 sec of HSI ignitor on period, atrial-for-ignition sequence occurs as described above forgas heating. After flame is proved and without blower ondelay, blower motor BLWM then operates on high-gas-heat speed during defrost. For both single-speed and2-speed heat pumps, defrost mode is in high-gas heat only.c. When furnace control R to W/W1 circuit is opened, furnacecontrol CPU begins normal inducer post-purge period, andblower motor BLWM remains on for blower off delayperiod. If R-G circuit remains closed, blower motorBLWM reverts to continuous operation.START-UP PROCEDURES1. Component test—The furnace features a component testsystem to help diagnose a system problem in case of compo-nent failure. To initiate component test procedure, ensure thatthere are no thermostat inputs to control and that all timedelays have expired. Short TWIN/TEST terminal to ground orCOM for 1 to 4 sec. See Fig. 10 for terminal locations.NOTE: The component test feature will not operate if control isreceiving any thermostat signals and until all time delays haveexpired.The component test sequence is as follows:a. The furnace control checks itself, operates inducer motoron low speed for 7 sec and on high speed for 7 sec, thenstops.b. The hot surface ignitor is then energized for 15 sec, thende-energized.c. The blower motor operates on low-gas-heat/heat pumplow-heat/low-cool/continuous fan speed for 7 sec, thenstops.d. The blower motor operates on high-gas-heat speed for 7sec, then stops. The gas valve and humidifier terminalHUM are not energized for safety reasons.NOTE: The EAC terminals are energized when blower is ener-gized.e. The blower operates on heat pump high-heat/high-coolspeed for 7 sec, then stops.2. After all connections have been made, purge gas lines andcheck for leaks.Never purge a line into a combustion chamber. Never usematches, candles, flame, or other sources of ignition to checkfor gas leakage. Use a soap-and-water solution to check forgas leaks. A failure to follow this warning could result in fire,explosion, personal injury, or death.3. To operate furnace, follow procedures on operating instructionlabel attached to furnace.4. With furnace operating, set thermostat below room tempera-ture and observe that furnace goes off. Set thermostat aboveroom temperature and observe that furnace restarts.ADJUSTMENTS1. Set gas input rate.Furnace gas input rate on rating plate is for installations ataltitudes up to 2000 ft.In the U.S.A., input rating for altitudes above 2000 ft must bereduced by 4 percent for each 1000 ft above sea level.In Canada, input rating must be derated by 10 percent foraltitudes of 2000 ft to 4500 ft above sea level.Furnace input rate must be within ±2 percent of input onfurnace rating plate.2. Determine natural gas orifice size and manifold pressure forcorrect input.a. Obtain yearly heat value average (at installed altitude) fromlocal gas supplier.b. Obtain yearly specific gravity average from local gassupplier.c. Verify furnace model. Table 9 can only be used for model58DXT Furnaces.d. Find installation altitude in Table 9.NOTE: For Canada altitudes of 2000 to 4500 ft, use U.S.A.altitudes of 2001 to 3000 ft in Table 9.e. Find closest natural gas heat value and specific gravity inTable 9.f. Follow heat value and specific gravity lines to point ofintersection to find orifice size and low- and high-heatmanifold pressure settings for proper operation.EXAMPLE: (0—2000 ft altitude)Heating value = 1075 Btu/cu ftSpecific gravity = 0.62Therefore: Orifice No. 45Manifold pressure: 3.7-in. wc for high heat1.5-in. wc for low heat* Furnace is shipped with No. 45 orifices.In this example, all main burner orifices are the correct sizeand do not need to be changed to obtain proper input rate.g. Check and verify burner orifice size in furnace. NEVERASSUME ORIFICE SIZE; ALWAYS CHECK ANDVERIFY.3. Adjust manifold pressure to obtain input rate.a. Remove caps that conceal adjustment screws for low- andhigh-heat gas valve regulators. (See Fig. 15.)b. Move setup switch SW-2 on control center to ON position.(See Fig. 13.) This keeps furnace locked in low-heatoperation.c. Jumper R and W/W1 thermostat connections on controlcenter to start furnace.d. Turn low-heat adjusting screw (5/64 hex Allen wrench)counterclockwise (out) to decrease input rate or clockwise(in) to increase input rate.NOTE: DO NOT set low-heat manifold pressure less than 1.3-in.wc or more than 1.7-in. wc for natural gas. If manifold pressure isoutside this range, change main burner orifices.15