A.O. Smith 197835-001 Water Heater User Manual


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CONTROLS AND SWITCHES
Thismodelisprovidedwiththreepressureswitches.Theseswitches
areessentialtothesafeandproperoperationoftheunit.Allswitches
arewiredinseries.Thecontrollerissetuptoshuttheunitdown
wheneverthereisafailureofanyoftheswitches.Itisimportantto
understandthepurposeofeachswitch.
FIGURE 12.
BLOWER PROVER SWITCH
(SEEFIGURE12)
TheBlowerProverSwitchisprovidedontheheatertoverifythat
thefanisoperating.Itisapositivepressureswitchwhoseelectrical
contactsarenormallyopen.Whenthefanincreasesthepressure
intheburner,thepressureswitchwillallowtheelectricalcontacts
toclose.Thepressureswitchisconnectedtotheburnertapbya
pieceoftygontubing.Thistubingmustbeconnectedinorderfor
theswitchtochangetheelectricalcontacts.Thecontrollerrequires
thattheelectricalcontactsonthisairowswitchbeopenbeforeit
willallowtheblowertocomeon.
BLOCKED EXHAUST SWITCH
(SEEFIGURE12)
TheBlockedExhaustSwitchissetuptoshuttheunitoffwhena
build-upofpositivepressureintheexhaustventpipeoccurs.This
switchisapositivepressureswitchthatrequiresanincreasein
pressuretochangetheelectricalcontactsfromnormallyclosedto
open.Whenthisswitchpreventstheunitfromigniting,mostlikelythe
exhaustisblockedbysomemeans.Checktoseeifthecondensate
isallowedtoowfreelyfromtheexhaustelbowandforobstructions
intheexhaustventingandexhaustventterminal.Alsoverifythat
theventlengthdoesnotexceedthemaximumallowedasshownin
theVentSectionofthismanual.
BLOCKED INTAKE SWITCH
(SEEFIGURE12)
TheBlockedIntakeSwitchissetuptoshuttheunitoffwhena
build-upofnegativepressureintheintakeairpipeoccurs.This
switchisanegativepressureswitchthatrequiresanincreasein
negativepressuretochangetheelectricalcontactsfromnormally
closedtoopen.Theswitchisconnectedtothepressuretaponthe
PVCpipeconnectedtotheinletoftheblower.Whenthisswitch
preventstheunitfromigniting,mostlikelytheintakeisblocked.
Verifythatthescreenontheintakeairconnection(conventional
vent),theintakeairpipeandtermination(directventinstallations)
arefreeofobstructionsthatmaypreventairfromenteringtheunit.
Insurethescreenonintakeairconnectionhasbeenremovedon
directventinstallations,seeFigure18B.Alsoverifytheintake
airpipelengthdoesnotexceedthemaximumallowedasshown
intheVentSectionofthismanual.
ON/OFF SWITCH
TheON/OFFSwitchisasingle-pole,single-throwrockerswitch.This
switchprovides120Vfromthelinesourcetotheheater.
CAUTION
THE WATER HEATER IS POLARITY SENSITIVE. BEFORE
APPLYING ELECTRICITY TO THIS HEATER BE CERTAIN THAT
SUPPLY NEUTRAL WIRE TO GROUND CHECK INDICATES
ZERO VOLTAGE.
HOT SURFACE IGNITER
TheHotSurfaceIgniterisadevicethatignitesthemainburnerby
hightemperature(>1800°For>982°C).When120VACisapplied
totheigniter,sufcientheatisgeneratedtoignitethemainburner.
Althoughimprovementshavebeenmadetostrengthentheigniter,
itisstillfragileandcaremustbetakenwhenhandlingtheigniterto
preventbreakage.
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