Service manual

20
Service Information
Attheearlieststageofdevelopmentworkon
R-134a,testswerecarriedoutonadifferenttypeof
syntheticoilknownasPoly-AlkalineGlycol(PAG).
Thisoilisalsousedincertainairconditioning
systemsforcars.PAGandEsteroilDONOTmix
withoneanother.Serviceequipmentusedfor
R-134a/Esteroilmustnotcomeintocontactwith
PAG.
Water In The Refrigeration
System
Eveninverysmallquantities,waterinany
refrigerationsystemcancausethefollowing
problems:
•Iceplugsincapillarytubes.
•Copperplatingincompressor.
•Reactionswithorganicmaterialsinsystems.
•Corrosionofmetals.
R-134aandEsteroilwillaggravatetheproblem
ofwaterintherefrigerationsystem.Esteroilmay
reactwithwatervaporandishydroscopic(itwill
absorbwaterifitcomesincontactwithhumidair).
WaterisalsomoresolubleinR-134athanR-12.
Tominimizethewatercontentwheneverservice
workisperformed,therefrigerationsystemshould
alwaysbethoroughlyevacuatedthroughprocess
tubeadaptorsonboththehighandlowsidesof
thesystem.Evacuationmustbeforaminimum
of30minutestoatleasta29.9inch(500micron)
vacuum.
Toachievetherequired29.9inch(500micron)
vacuum,aproperlymaintainedtwo-stagevacuum
pumpingoodconditionisrequired.Atwostage
pumpcanreachadeepervacuumthanasingle
stagebecausetheexhaustfromtherstpumping
stageisdischargedintothesecondpumpingstage.
Thismeansthesecondstagebeginspumpingata
lowerpressuresoalowerultimatevacuumcanbe
achieved(See2-StageVacuumPump,FigureE3).
VACUUM CHART
Vacuum
Inches Hg.
Microns
Boiling Point
of Water °F
28.940 25000 77.9
29.530 10000 52.0
29.832 4600 32.0
29.882 1000 1.0
29.901 500 -11.2
29.915 150 -32.8
29.917 100 -38.2
29.919 50 -49.0
Vacuum Pump Maintenance
Itisabsolutelyessentialtomaintainyourvacuum
pumpaccordingtothemanufacturer’sinstructions
includingrequiredoilchangesattherecommended
intervals.Vacuumpumpoilshouldalwaysbe
changedafterevacuatingacontaminatedsystem.
Vacuumpumpperformanceshouldbechecked
periodicallywithamicrongauge.
Vacuumpumpsuppliersmayormaynot
recommendchangingthevacuumpumpoiltothe
sametypethat’sinthesystembeingevacuated.
Somemanufacturersmayrecommendavacuum
pumpthat’sdedicatedtoR-134asystems.
Robinairhasstatedthattheircurrentand
discontinuedvacuumpumpmodels,usingmineral
oilcurrentlyspeciedforuseintheirvacuum
pumps,canbeusedtoevacuateR-134a/Esteroil
systems.Robinairalsostatesthatitisacceptable
toalternatebetweenevacuatingR-12/mineraloil
andR-134a/Esteroilsystemswithoutadversely
effectingthevacuumpump’sperformance.
Forotherbrandsofvacuumpumps,checkwiththe
manufacturerforrestrictionsandguidelineswhen
usingwithR-134a.
2-Stage Vacuum Pump
Figure E3