A.O. Smith 197835-001 Manual

A SERVICE OF

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28

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.