Carrier 58MCB Nstallation, Start-up, And Operating Instructions

Also see for 58MCB: User's information manual Service and maintenance instructions Owner's manual Service and maintenance instruction Installation, start-up, and operating instructions

Carrier 58MCB Nstallation, Start-up, And Operating Instructions Manual pdf 49 page image

-- 49 --HEATING MODE(See Fig. 30 for thermostat connections.)The wall thermostat “calls for heat”, closing the R to Wcircuit. The furnace control performs a self-check, verifiesthe pressure switch contacts PRS are open, and starts theinducer motor IDM.a. Inducer Prepurge Period -- As the inducer motorIDM comes up to speed, the pressure switch contactsPRS close, 24 vac power is supplied for a fieldinstalled humidifier at the HUM terminal and thecontrol begins a 15-second prepurge period.b. Igniter Warm-Up -- At the end of the prepurge period,the Hot-Surface Igniter HIS is energized for a17-second igniter warm-up period.c. Trial-for-Ignition Sequence -- When the igniter warmup period is completed the main gas valve relaycontacts GVR close to energize the gas valve GV, thegas valve opens. The gas valve GV permits gas flow tothe burners where it is ignited by the Hot SurfaceIgniter HSI. Five seconds after the GVR closes, a2-second flame period begins. The HSI igniter willremain energized until the flame is sensed or until the2-second flame proving period begins.d. Flame-Proving -- When the burner flame is proved atthe flame-proving sensor electrode FSE, the furnacecontrol CPU begins the blower-ON delay period andcontinues to hold the gas valve GV open. If the burnerflame is not proved within two seconds, the controlCPU will close the gas valve GV, and the control CPUwill repeat the ignition sequence for up to three moreTrials-For-Ignition before going to Ignition-Lockout.Lockout will be reset automatically after three hours,by momentarily interrupting 115 vac power to thefurnace, or by interrupting 24 vac power at SEC1 orSEC2 to the furnace control CPU (not at W,G,R, etc.)If flame is proved when flame should not be present,the furnace control CPU will lock out of Gas-Heatingmode and operate the inducer motor IDM until flameis no longer proved.e. Blower-On Delay -- If the burner flame is proven, theblower motor is energized on HEAT speed 66 seconds(040 through 120 sizes) or 45 seconds (140 size) afterthe gas valve GV is energized.Simultaneously, the electronic air cleaner terminalEAC--1 is energized and remains energized as long asthe blower motor BLWM is energized.f. Blower-Off Delay -- When the thermostat is satisfied,the R-to-W circuit is opened, de-energizing the gasvalve GV, stopping gas flow to the burners, andde-energizing the humidifier terminal HUM. Theinducer motor IDM will remain energized for a15-second (040 through 120 sizes) or 5-second (140size) post-purge period. The blower motor BLWM andair cleaner terminal EAC--1 will remain energized for90, 120, 150, or 180 seconds (depending on theblower-OFF delay selection). The furnace control CPUis factory-set for a 120-second blower-OFF delay.COOLING MODE(See Fig. 30 for thermostat connections)The thermostat closes the R-to-G-and-Y circuits. The R-to-Ycircuit starts the outdoor unit, and the R-to-G and Y circuits startthe furnace blower motor BLWM on COOL speed.The electronic air cleaner terminal EAC--1 is energized with115 vac when the blower motor BLWM is operating.When the thermostat is satisfied, the R-to-G-and-Y circuits areopened. The outdoor unit will stop, and the furnace blower motorBLWM will continue operating on the COOL speed for anadditional 90 seconds. Cut jumper J2 to reduce the coolingoff-delay to 5 seconds.CONTINUOUS BLOWER MODEWhen the R-to-G circuit is closed by the thermostat, the blowermotor BLWM will operate on continuous-blower speed (same asHEAT speed). Terminal EAC--1 is energized as long as theblower motor BLWM is energized.During a “call for heat,” the blower BLWM will stop duringigniter warm-up (17 seconds), ignition (7 seconds), andblower-ON delay (66 or 45 seconds for 040 through 120 sizes orfor 140 size), allowing the furnace heat exchangers to heat upmore quickly, then restarts at the end of the blower-ON delayperiod at HEAT speed. In heating, the furnace control CPU willcontinue running the blower motor BLWM at HEAT speed afterthe selected blower-OFF delay period is completed.When the thermostat “calls for cooling”, the blower motorBLWM will operate at COOL speed. When the thermostat issatisfied, the blower motor BLWM will operate an additional90 seconds on COOL speed before reverting back to HEATspeed. Jumper J2 can be cut to reduce the cooling off-delay to 5seconds. (See Fig. 33.) When the R-to-G circuit is opened, theblower motor BLWM will continue operating for an additional5 seconds, if no other function requires blower motor BLWMoperation.HEAT PUMP MODEWhen installed with a heat pump, the furnace controlautomatically changes the timing sequence to avoid long bloweroff times during demand defrost cycles. When the R-to-W-and-Yor R-to-W-and-Y-and-G circuits are energized the furnace controlCPU will continue to turn on the blower motor BLWM at HEATspeed, and begin a heating cycle. The blower motor BLWM willremain on until the end of the prepurge period, then shut off for24 seconds then come back on at HEAT speed. When the W inputsignal disappears, the furnace control begins a normal inducerpost-purge period and the blower switches to COOL speed after a3 second delay. If the R-to-W-and-Y-and-G signals disappear atthe same time, the blower motor BLWM will remain on for theselected blower-OFF delay period. If the R-to-W-and-Y signalsdisappear, leaving the G signal, the blower motor BLWM willcontinue running the blower motor BLWM at HEAT speed afterthe selected blower-OFF delay period is completed.Control initiates a 90-sec blower only on period before startinganother heat pump cycle if there is a power interruption. Anytimecontrol senses false flame, control locks out of heating mode.This reaction occurs because control ignores W input due to falseflame signal and, as a result, sees only Y input and goes intocooling mode blower off delay. All other control functions remainin standard format.NOTE: EAC--1 terminal is energized whenever blower operates.HUM terminal is only energized when gas valve is energized.COMPONENT TESTNOTE: The furnace control component test allows allcomponents to run for a short time; except the gas valve andhumidifier terminal HUM are not energized for safety reasons.The EAC--1 terminal is energized when the blower is energized.This feature helps diagnose a system problem in case of acomponent failure. The component test feature will not operate ifany thermostat signal is present at the control and not until alltime delays are completed.58MCB