Carrier 58MSA Installation, Start-up, And Operating Instructions Manual

Also see for 58MSA Series: Service and maintenance instructions User manual Instruction manual Installation, start-up, and operating instructions Installation, start-up, and operating instructions

Carrier 58MSA Installation, Start-up, And Operating Instructions Manual Manual pdf 42 page image

EXAMPLE: (0—2000 ft altitude)Furnace input from rating plate is 100,000 Btuh.Btu heating input = Btu/cu ft X cu ft/hrHeating value of gas = 975 Btu/cu ftTime for 1 revolution of 2-cu ft dial = 70 secGas rate = 103 cu ft/hr (from Table 11)Btu heating input = 103 X 975 = 100,425 BtuhIn this example, the orifice size and manifold pressureadjustment is within ±2 percent of the furnace input rate.SET TEMPERATURE RISETemperature rise must be within limits specified on furnacerating plate. Recommended operation is at midpoint of riserange or slightly above. Failure to follow this caution mayresult in primary and secondary heat exchanger failure.Determine and adjust air temperature rise as follows:1. Place thermometers in return and supply ducts as close tofurnace as possible. Be sure thermometers do not see heatexchanger so that radiant heat does not affect readings. Thispractice is particularly important with straight-run ducts.2. When thermometer readings stabilize, subtract return-air tem-perature from supply-air temperature to determine air tem-perature rise.3. Adjust temperature rise by adjusting blower speed. Increaseblower speed to reduce temperature rise. Decrease blowerspeed to increase temperature rise.Disconnect 115-v electrical power before changing speed tap.Failure to follow this warning could result in personal injury.4. To change blower motor speed selections for heating mode,remove blower motor lead from control center HEAT termi-nal. (See Fig. 33.) Select desired blower motor speed leadfrom 1 of the other motor leads and relocate it to HEATterminal. See Table 12 for lead color identification. Reconnectoriginal lead on SPARE terminal.Follow this same procedure for proper selection of COOLspeed selection.BLOWER OFF DELAY (HEAT MODE)The blower off delay has 4 adjustable settings from 90 sec to 180sec. (See Table 13.) The blower off delay jumpers are located onthe furnace control board. (See Fig. 33.) To change the blower offdelay setting, move the jumper from one set of pins on the controlboard to the pins used for the desired blower off delay. Factoryblower off delay setting is 120 sec.Table 13—Blower Off Delay Setup PositionPINS 1 AND 2 2 AND 3 3 AND 4 4 AND 5Time (in sec) 90 120 150 180SET THERMOSTAT HEAT ANTICIPATORWhen using a nonelectronic thermostat, the thermostat heatanticipator must be set to match amp draw of components in R-Wcircuit. Accurate amp draw measurements can be obtained atthermostat subbase terminals R and W. Fig. 49 illustrates an easymethod of obtaining these measurements. The amp reading shouldbe taken after blower motor has started and furnace is heating.Connect ammeter wires as shown in Fig. 49. The thermostatanticipator should NOT be in the circuit while measuring current.If thermostat has no subbase, the thermostat must be disconnectedfrom R and W wires during current measurement. See thermostatmanufacturer’s instructions for adjusting heat anticipator and forvarying heating cycle length.For an electronic thermostat, set cycle rate for 3 cycles per hour.CHECK SAFETY CONTROLSThis section covers the safety controls that must be checked beforethe installation is complete. The flame sensor, gas valve, andpressure switch were all checked in the Start-up procedure sectionas part of normal operation.Step 1—Check Primary Limit ControlThis control shuts off gas control system and energizes air-circulating blower motor if furnace overheats. Recommendedmethod of checking this limit control is to gradually block offreturn air after furnace has been operating for a period of at least5 minutes. As soon as limit control has shut off burners, return-airopening should be unblocked to permit normal air circulation. Byusing this method to check limit control, it can be established thatlimit is functioning properly and operates if there is a restrictedreturn-air duct or motor failure. If limit control does not functionduring this test, cause must be determined and corrected.Table 12—Speed SelectorCOLOR SPEEDFACTORY-SHIPPEDCONNECTIONBlack High CoolYellow (When Present) Medium High SpareBlue Medium Low HeatRed Low SpareWhite Common ComFig. 49—Amp Draw Check with AmmeterA80201R Y W G10 TURNSTHERMOSTAT SUBBASETERMINALS WITHTHERMOSTAT REMOVEDHOOK-AROUNDVOLT/AMMETEREXAMPLE: 5.0 AMPS ON AMMETER10 TURNS AROUND JAWS = 0.5 AMPS FOR THERMOSTAT SETTINGFROM UNIT 24-VOLTTERMINAL BLOCK42