DOMETICDometicMANUAL REFRIGERATORDIAGNOSTIC SERVICEMANUALThe Dometic C o r p o r a t i o n2320 Industrial ParkwayElkhart, IN 46515219-295-5228Corporate OfficeWarrantyDepartment205 E. Fenn St.LaGrange, IN 46761219-463-2191Technical Services509 S. Poplar St.LaGrange, IN 46761219-463-4858DepartmentOS1286 8/89D-lDiagnostic Service Manuals


MANUAL REFRIGERATORDIAGNOSTIC SERVICE ‘MANUALTable of ContentsPageDiagnostic Flow ChartsNo Operation . . . . . . . . . . . . .D-4-lNo 12OV AC Operation . . . . . . . . .D-4-2No Gas Operation (Piezo Igniter)D-4-3. . . .No Gas Operation (Automatic Reigniter).D-4-4Operation and Diagnosis.D-6- 1. . . . . . . . . . . .D-8-lDometic M a n u a l R e f r i g e r a t o r s .GlossaryofService BulletinsTerms.D-3.D-9-l

MANUAL REFRIGERATORDIAGNOSTIC FLOW CHARTNO OPERATIONA.1Check Supply VoltageI 1C o r r e c t1. 110 Volt Plug2. Wire SizeasNecessaryOKB.VCheck FuseNOT OKCorrect as Necessary Replace if DefectiveOKC.\/ Correct as NecessaryCheck wiringNOT OK1OKD.Check Switch Correct as NecessaryNOT OK(Page D-6-20, Para. 66)OKE.VCheck ThermostatNOT OKD-4-l, Correct as Necessary’ Continuity Check

MANUAL REFRIGERATORDIAGNOSTIC FLOW CHARTNO 120 VOLT AC OPERATIONA. AC PowerRefrigerator Plugged in I i Correct as NecessaryBreakerCoach PlugOKB.wCheck Selector SwitchNOT OKCorrect as Necessary(Page D-6-20, Para. 66)OKc .VCheck ThermostatNOT OKD.IIfCorrect as NecessaryContinuity CheckOKCheck 120 Volt HeaterNOT OKD-4-2Correct as NecessaryB Ohm’s ReadingBulletin #28(Page D-9-l 4, D-9-l 5)

MANUAL REFRIGERATORDIAGNOSTIC FLOW CHARTNO GAS OPERATION - Models Equipped with Piezo igniter9.Check Gas SupplyOKB.vCheck SwitchCorrect as Necessary(Page D-6-20, Para 66) NOT OKIOK.C.Check ThermostatNOT OKCorrect as Necessary Continuity CheckOKVD.Check Gas PressureNOT OKCorrect as Necessary(Page D-6-13, Para. 37) OK Check Flue & BurnerNOT OKICorrect as NecessaryNo ObstructionsOKF.Check Piezo ResistanceCorrect as Necessary(Page D-6-l 8, Para. 58) NOT OKIVG.OKrPara Replace Electrod (Page D-6-18, Para. 58)Check Piezo ElectrodeNOT OKIOK,H.VCheck Spark Gapof Electrode to BurnerNOT OKD-4-3 Correct as Necessary(Page D-6-19, Para. 62)

MANUAL REFRIGERATORDIAGNOSTIC FLOW CHARTNO GAS OPERATION - Models Equipped with Automatic ReigniterA.Check Gas PressureNOT OK Correct as Necessary(Page D-6-13, Para 37)IOKVB.Check Gas Supply Correct as Necessary(Page D-6-14, Para. 40)NOT OKIC.IvOKCheck 12 Volt D.C.Supply Correct as NecessaryNOT OKIIOKCheck SwitchNOT OKIBCorrect as Necessary(Page D-6-20, Para. 66)OKE.Check ThermostatNOT OK Correct as NecessaryCheck for ContinuityOKF.VClean Assembly & Orifice as NecessaryCheck Flue & BurnerNOT OKI,G.IOKVCheck Electrode NOT OKReplace Electrode(Page D-6-19, Para. 62)



(1)This is Dometic’s Manual Refrigeration Diagnosis and Troubleshooting program. In this programwe will discuss the way an absorption cooling unit operates, and the diagnostic proceduresused to troubleshoot the complete refrigerator system.(2)Before we begin extensive troubleshootingprocedures on the cooling unit, let’s take a fewminutes to see how it operates.THE ABSORPTION SYSTEM(3)The sealed combustion unit contains amixture of ammonia, water and a rustinhibiting agent. After this solution isintroduced into the coils, this unit ispressurized with hydrogen gas. Whenthis system is in operation, the ammonia vaporizes in the hydrogen atmosphere and absorbs heat from insidethe refrigerator.EVAPORATORGASTEMPERATUREEXCHANGERLil IABSORBERVESSELD-6-2BOILER.

(4)\ PUMPThe cooling unit parts that accomplish this‘cooling’ or heat extraction process, include the:Boiler or Generator/ IIGASTEMPERATUREXCHANGER- - - - - - - - - - - --.I1(6)EvaporatorD-6-3

(7)AbsorberABSORBERTHE ABSORPTION SYSTEMCONDENSEREVAPORATORBecause the self-contained cooling unitdoes not utilize an electric compressoror pump, the cooling coils can be operated from a variety of heat sources. LPgas, 120 volts AC and 12 volts DCheating elements are the most commonly used heat sources for recreational vehicle GER(9)THREE REQUIREMENTSFOR PROPER OPERATIONBefore this cooling system can properlyextract heat from the cabinet of therefrigerator, three requirements for proper refrigerator operation must be met.These are precise heat, specified ventilation and proper leveling.1. Level2. Air Flow (Ventilation)3. HeatD-6-4

c--- ------- --------- ---- - -7II(10)We will now take a closer look at how thecooling unit functions in normal operation.When proper heat is supplied to the boiler,ammonia vapor is produced and rises in thesiphon pump, carrying with it a weak liquidammonia solution. As seen from this drawing,the siphon pump, or pump tube, is an internalarrangement within the boiler section. The boilersection utilizes the ammonia-water liquid solution in the absorber and as it is heated, turnsthe solution into a strong ammonia vapor, whichis needed to operate the system. This strongammonia vapor rises from the pump tube to thecondenser coil.Any deviation from the listed amount ofheat to the absorption system will alter theammonia to water ratio, which, in turn, willdecrease the cooling unit’s overall efficiency.The weak ammonia solution which remainsbehind is diverted to the top of the absorbercoils to perform a function that we will discussin further detail later in the program.IWATER1ENSERiI------------------------ PUMP/PI(11)The air that passes through the condenser fins,from the venting system, removes heat from theammonia vapor, causing it to condense into astrong liquid ammonia solution. As a liquid, itthen flows to the low temperature evaporator, orfreezer companment, where it comes intocontact with a hydrogen atmosphere. When thisoccurs, the ammonia begins to evaporate whichdraws heat from inside the freezer section, tothe rear of the cooling unit.COLD INTERIOR(12)This heat is then dissipated out through theupper vent, which allows the refrigeratorsinterior temperature to properly maintain foodstorage requirements. Not all of the liquidammonia evaporates in the freezer. What is leftcontinues to evaporate as it flows to the hightemperature evaporator, or food storage compartment.D-6-5

I--U 3)As this process continues, the ammonia andhydrogen vapors become intermixed and flowdownward into the absorber vessel. As theammonia vapor comes in close contact to theliquid ammonia solution in the absorber vessel,the ammonia is absorbed into the liquidsolution, allowing the hydrogen vapor to rise upthrough the absorber coils. After this absorptionprocess, the vapor consists of mostly hydrogenwith some traces of ammonia.I1IIIIII-------Ll i(14)To remove the remaining amounts of ammoniavapor still present in the hydrogen, acontinuous flow of weak ammonia solution isfed, by gravity, to the top of the absorber coilfrom the boiler. As this weak ammonia solutionflows downward through the absorber, itabsorbs the ammonia vapor from the mixture,allowing the hydrogen vapor to rise through theabsorber coil and return to the evaporator. Withthe hydrogen returned to the evaporator andthe ammonia remixed into solution in theabsorber vessel, the cooling process cancontinue.I --- -----(15)Now that we have a basic understanding ofproper cooling unit flow and operation, let’stake a step-by-step look at the three requirements for proper cooling unit operation. Pleasenote it is essential that these three requirementsbe diagnosed before attempting to diagnosethe cooling unit. A problem with leveling, heatinput or ventilation may lead you to think thatthe cooling unit is faulty, when actually it is not.This causes an increased expense to you, thecustomer, and valuable shop time is wastedbecause of incorrect diagnosis, By followingand checking the three unit requirements, costlydiagnostic errors can be eliminated.THREE REQUIREMENTSFOR PROPER OPERATION1. Level2. Air Flow (Ventilation)3. HeatD-6-6IA

(16)THREE REQUIREMENTSFOR PROPER OPERATION1. LevelSince the absorption system utilizes nomechanical pumps or compressors to circulatethe refrigerant within the system, proper levelingis required to provide correct refrigerant flow inthe gravity-feed system. Without proper leveling,refrigerant within the cooling coils will collectand stagnate at certain areas. When thishappens the cooling process will stop.(17)On the older style cooling units equipped withsquare boiler box covers, this condition cancause permanent cooling unit failure. As we cansee from this drawing, square boiler boxcooling units utilize an exposed siphon pumptube which will become excessively superheated in an out-of-level condition. This canallow the rust inhibiting agent to chemicallybreak down and permanently block or restrictthe normal refrigerant flow through the pump.Shaking, tipping or so called ‘burping therefrigerator will not loosen or dislodge theblockage. The only recommended serviceprocedure is to replace the cooling unit. Toprevent this occurrence, proper leveling is ofutmost importance when the RV is parked forany length of time.REFRIGERATOR IS TO BE LEVEL(18)LEVELSTo level these units, the spirit or bubble levelshould be placed in the approximate front andcenter of the floor of the freezer compartment.The coach should then be positioned so that atleast 3/4 of the bubble is within the requiredmark while the refrigerator is in operation.REMEMBER: Failure to property level a squareboiler box can result in a lack of cooling orpermanent damage to the coding unit. W h e nthe vehicle is moving, leveling is not critical asthe rolling and pitching movement of the RV willkeep the solution in motion, preventing thesolution from accumulating in the piping.- m- C Z-5D-6-7

(19)In recent years Dometic has engineered a newtype of cooling unit that utilizes an improvedsiphon pump tube design which drasticallyreduces the possibility of permanent damage tothe coils if operated in an out-of-level condition,or too much heat is generated at the boilersection. As we can see from this drawing, thesiphon pump tube is enclosed in the designand is surrounded by a weak ammonia solution,which will protect the pump tube from abnormally over-heating. This type of unit; however,does not eliminate the need for proper leveling.The unit still requires gravitational flow toprovide the proper cooling process, and ifleveling is outside the necessary limits, coolingwill dramatically slow down or stop completely.The cooling coils are not normally damaged inthis fashion and once proper leveling is maintained, the cooling process will resume.\ PUMPIIIIIIIIIIIIIIII(20)Spirit or bubble levels are no longer beingsupplied with the new style refrigerators as theRV or vehicle only needs to be leveled so it iscomfortable to live in, with no noticeable slopingof the floor or walls. For diagnosis, the newstyle cooling units that incorporate theprotection boiler system, can be differentiatedfrom the older style coils by the shape anddesign of the outer boiler box cover on the rearof the cooling unit. These units will incorporatea circular metal cover,. . .while the older style utilizes a squareshaped enclosure. We will discuss diagnosisand troubleshooting of these units in moredetail later in the program.

(22)THREE REQUIREMENTSFOR PROPER OPERATIONThe coach vent system must be able to providea way to direct the hot air, produced by theaction of the cooling unit, out away from theinstallation of the refrigerator.1. Level2. Air Flow (Ventilation)-------- -----(23)In a good installation there should be as littleopen space as possible surrounding the sidesand top of the refrigerator to achieve proper airflow. All potential dead air pockets should beblocked or baffled to insure that heat from thecooling unit won’t be trapped in these spacesand reduce efficiency. In addition, the coolingunit should be at least one inch from thenearest surface made of combustible materials.Please follow the installation manual for properdimensions and clearances.RVIA requires that the refrigerator beinstalled in such a manner as to providecomplete separation of the combustion systemand the interior atmosphere of the recreationalvehicle. This regulation requires all seams andjoints in the enclosure be sealed. The undercounter installation is different. The addition ofa metal chute the width of the enclosure, thatextends from the upper side vent, will helpeliminate the possibility of dead air pockets. Ithelps direct the hot air out the exhaust vent.The best method for venting the absorptionrefrigerator is with a lower side vent and a roofvent. Using proper Dometic vents will give yousufficient intake and exhaust areas for ventilation1II0" CLEARANCE1" FROMAIR FLOW.,/‘,/, .i.,l I,,,, ,. n/II- - - - - - - - - - - -(24)Heat application to the boiler section of thecooling unit must be within the designed BTU’s.Never oversize the heating element on AC orDC power source. Always use the proper sizeorifice for gas modes. As explained earlier, anydeviation will cause a potential cooling unitfailure.IIIJTHREE REQUIREMENTSFOR PROPER OPERATION1. Level2. Air Flow (Ventilation)3. HeatD-6-9

THE ABSORPTION SYSTEM(25)Three things must be rememberedwhen diagnosing a cooling unit:First, circulation within the cooling unit is totally gravitational. Thismeans proper leveling is important.Second, heat - created to boilthe ammonia - now has to be dissipated into the surrounding air. Heatfrom the absorber and condenser mustalso be dissipated so as to cool theammonia sufficiently.Third, proper heat application atthe boiler LER(26)DIAGNOSINGTHECOOLING UNITWhen diagnosing a cooling unit, remember thisis the only part we cannot field check with testequipment, yet it is the simplest and quickestpart to diagnose.(27)After the unit has been operating forapproximately one hour, carefully touch the unitat the boiler box and the absorber area. Theseareas should be approximately the sameof the ambienttemperature,regardlesstemperature. Equal heat between the boiler andthe absorber indicates the fluid circulation withinthe unit is good.TEMPERATUREbGOOD CIRCULATIOND-6-10

(28)One of the faults with a cooling unit isa blockage. This can happen when theunit is operated off-ievel, or if too muchheat has been applied to the boilerarea. To the touch, this unit will beextremely hot at the boiler with littlewarmth at the absorber. In other words,no circulation.i --TG-- BOILER(29)This type of fault means a lost charge.It is known as a ‘leaker’. To the touch,this unit will be warm at the boiler andextremely hot at the absorber. In thiscondition we are still boiling ammoniabut have no hydrogen for evaporation.HOT GAS ONLY(30)The following section of the programexamines the Dometic manual refrigerator’s gas and electrical systems.Dometic refrigerators are designed forboth piezo and automatic ignition. Bothsystems will be covered in this presentation.D-6-1 1WARMBOILER. i

UNDERSTANDINGTHEGAS SYSTEM(31)Let’s look at the current Dometic refrigeratorsand see how the gas flows.SHUT-OFFVALVE(32)Gas flows from the gas line to the shut-off valveand to the connection piece.I cYz zcGAS LINECONNECTIONPIECE(33)COMBINATIONGAS & ELECTRICTHERMOSTATinto the combination gas and electric thermostat(34)WSAFETY VALVE/through the safety valve thermocouplePRESSURETESTHOUSING(35)test housingD-6-12v”

(36)and onto the orifice and burner assembly.Remember that except for the connection piece,all fittings are O-ring sealed. Whenever thesystem is separated the O-rings must bereplaced.ORIFICE & BURNERASSEMBLY(37)To diagnose the gas system, connect amanometer to the test point. With thethermostat on maximum you must have 11inches water column pressure at this point. Ifyou have 11 inches pressure, your problemIs to the right of the test point. If you do nothave 11 inches water column pressure, theproblem Is to the left.f ? DIAL SHAFT(38)Let’s take a closer look at the gas thermostat.In this drawing we will review how a thermostatfunctions. When the thermostat is workingproperly, the manometer will read line pressurewhen set at maximum and the refrigerator istrying to cool. From this drawing you can seethe gas flow when the refrigerator is trying tocool. The gas flows through the thermostat atline pressure without restriction. The valve isopen at this time.VALVE DIAL SHAFTq. /--c(39)The valve is now closed and the gas must flowthrough the by-pass screw; the gas is nowdiverted through the by-pass screw, whichregulates the size of the low flame. Thiscondition can only exist when the refrigerator iscold or the thermostat is set to minimum or off.If the sensing tube has lost its pressure, evenwith the thermostat set on maximum, you willhave only low flame.i&‘-TSCREWD-6-13w--CLOSED VALVE,-

(40)The most efficient way to diagnose the gassystem would be to first connect the gasmanometer to the pressure test point. With thethermostat set at maximum you must have 11to 12 inches water column pressure for therefrigerator to operate properly. If yourmanometer reads higher than 11 to 12 incheswater column pressure, the tank regulator isadjusted to high, readjust it. Make sure thegas system has at least 50% of the coach’s LPappliances on at the time the system is beingadjusted. If the manometer reads 11 inches, theproblem of no cooling lies in the burnerassembly, flue pipe or venting.(41)If you have less than 11 inches water columnpressure, the next step would be to remove theby-pass screw.NOTE:The by-pass screwreduces the pressure andvolume of gas to the burner.(42)Shut off gas supply at the back of the refrigerator. Remove the by-pass screw from the top ofthe thermostat,Use a by-pass screw that does not have thesmall O-ring at the bottom. Reinstall this bypass screw into the thermostat.D-6-14

Turn on the main gas supply and take areading. If the manometer now reads 11 inches,the thermostat is defective and must bereplaced.(45)If the by-pass screw test shows no change ingas pressure, the problem lies with the gassupply to the refrigerator. Shut off the gassupply, remove the by-pass screw, replace itwith one that has an O-ring and turn on gassupply. Remember to check for a gas leak. Atthis time we will take a look at the rest of thegas system.(46)The safety valve, or flame failuredevice,consists of a brass alloy valve housing andcap, an electro-magnet, and a thermocouple,which generates 14 to 30 millivolts when heat isapplied to the tip. It is used to energize theelectro-magnet in the safety valve. The purposeof this device is to insure that the flow of gas isshut off in the event flame is lost at the burner.If this should occur, the thermocouple cools,the magnet loses it magnetic field and thevalve closes. Most failures of this device arerelated to the magnet, not the thermocouple.Should this happen, the complete safety valveshould be replaced.safetyD-6-15

(47)Once the gas has been allowed to passthrough the safety valve, it flows to the gas jetand burner. These have been specificallydesigned to eliminate most of the normal maintenance required due to the corrosive contaminants in the gas, as well as soot and rustwhich fall from the flue pipe. The jet has anorifice made of an industrial ruby which hasbeen laser-beam drilled. Each model ofDometic refrigerator uses a different size orificein order to maintain the required amount ofheat at the siphon pump. To clean the jet andburner, soak them in an alcohol base solventand allow to air dry. DO NOT use a pin orneedle. This will distort or shatter the orifice.(48)If you determine that disassembly is required,be aware there are two model designs formanual refrigerators. The design pictured herewill be discussed first.(49)Shut off the main gas supply, then disco