103 FN Troubleshooting

7/29/2019 103 FN Troubleshooting

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Danoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 185

Trouble

shooting

Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors

Contents Page

1.0 Compressor/system does not run (start) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

2.0 The compressor/system runs, but with reduced rerigeration capacity. . . . . . . . . . . . . . . . . . . . . . . . . . 190

3.0 Power consumption too high . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

4.0 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195


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186 DKRCC.PF.000.G1.02 / 520H1459 Danoss A/S (AC-DSL/MWA), 10 - 2006

Notes


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Trouble

shooting


1.0Compressor/systemdoes not run (start)

1.1

1.2

1.3

Main switch drop-out Blown use

Short-circuiting to rame

Motor deect

Deective current lead-in

Electrical equipment

Compressor Compressor motor/motor protector mechanically blocked.Overload

Voltage/requency

Pressure irregularity

Rerigerant type

Pressure equalisation

Fan drop-out

High and low-pressure switches Mechanical deect

Incorrect connection

Incorrect dierential setting

Incorrect cutout setting


Thermostat Mechanical deect

Incorrect connection

Dierential too small

Incorrect cutout value

I the main use blows, the cause must be ound.This will most oten be a deect in the motorwindings or motor protector, short-circuiting torame or a burnt current lead-in which, in turn,causes main use drop-out. I a compressor motorreuses to start, always check the resistancesrst. All compressors have their main and startwindings located as shown in the sketch.Resistance values are stated in the individual datasheets.

As a rule, a motor protection is built into allcompressor motors. I the winding protector cutsout the motor, due to the heat accumulated inthe motor the cut-out period can be relativelylong (up to 45 minutes). When the motor willno longer run, resistance measurement willconrm whether a motor protector has cut outor whether a winding is deective. A mechanicalseizure in the compressor will show itsel byrepeated start attempts accompanied byhigh current consumption and high windingtemperatures that cause motor protector cutout.

Compressor overload can be recognised by thecompressor reusing to start or by starting andthen stopping again ater a very short time (viathe motor protector). I the com-pressor is usedoutside its allowed application limits the usualresult is overload. Application limits such asvoltage tolerances, requencies, temperature/pressure and rerige-rant type are given in theindividual data sheet. In systems not protected bya high-pressure cut-out switch on the dischargeside, a an motor which is deective or cut outvia a motor protector can lead to compressoroverload. Generally, the rerigerant quantity

must be determined precisely. In capillary tubesystems the most certain method is to taketemperature measurements on the evaporatorand suction line.

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1.4

1.5

1.6

1.7

1.8

In systems with thermostatic expansion valve,charging must be checked using a sight glass. Inboth systems, the rerigerant quantity must beless than the quantity that can be accommodatedin the ree volume on the discharge side.

Compressors or capillary tube systems areusually equipped with a PTC LST startingdevice. Starting via a PTC requires completepressure equalisation between the high andlow-pressure sides on every start. In addition,beore it can operate, the PTC requires a standstilltime o about 5 minutes to ensure that thePTC component is cooled down in order to

achieve maximum starting torque. When a coldcompressor is started and the current is cut oa short time ater, conict can arise between thePTC and the motor protector. Because the motorretains heat, up to approx. 1 hour can elapsebeore normal start is possible.

In systems where pressure equalisation onstarting is not certain, the compressor must beequipped with an HST starting device. This alsoapplies to capillary tube systems with a standstilltime o less than 5 minutes. Deective or incorrectrelays and starting capacitors can cause starting

problems or that the compressor is cut out viathe motor protector. Note the manuacturerscompressor data. I the starting device is thoughtto be deective the whole equipment mustbe replaced, including the relay and startingcapacitor.

The PTC (25 or 220 V mains and approx. 5 or115 V mains) can be checked using an ohmmeter.

A starting relay can be checked with a lamp, seesketch. The relay is in order i the lamp does notlight up when the relay is upright. The relay is alsoin order i the lamp lights up when the relay isupside down.

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Trouble

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1.9

1.10

1.11

A starting capacitor can also be checked byapplying rated mains voltage to it or a ewseconds and then short-circuiting the leads. Isparks appear, the capacitor is in order.

In some markets, Danoss oers condensing unitswith combined high and low-pressure switchesthat protect the compressor against excessivepressure on the discharge side and too lowpressures on the suction side. I the high-pressureswitch has cut out the system, a check shouldbe made to see whether pressure irregularity isoccurring. I the low-pressure switch has cut out,the cause can be insufcient rerigerant amount,leakage, evaporator icing and/or partial blockageo the throttling device.I there is no pressure irregularity on the highor low-pressure sides, the pressure switch itsel

must be checked. See also the chapter Pressurecontrols.

The system can also cut out because o adeective or incorrectly set/sized thermostat.I the thermostat loses charge or i thetemperature setting is too high, the system willnot start. I the temperature dierential is set toolow, compressor standstill periods will be shortand there might be starting problems with anLST starting device and shortened compressorlie with an HST starting device. The guideline orpressure equalisation time using an LST startingdevice is 5 to 8 minutes or rerigerators and 7 to10 minutes or reezers.

I an HST starting device is used, the aim isto keep the cut-in periods per hour as ew aspossible. Under no circumstances must therebe more than ten starts per hour. See also thechapter Thermostats.

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2.0The compressor/systemruns, but with reducedrefrigeration capacity

2.1

2.2

2.3

Compressor Leakage

Coking

Pressure irregularity Blockage

Non-condensible gases

Moisture

DirtFan deect

Rerigerant loss

Rerigerant overcharge

Icing

Throttling device

Capillary tube/thermostatic expansion valve

Static superheat setting

Orice size/diameter

2.4

Frequent causes o reduced rerigeration capacityare coking, and copper plating which lead toreduced lie time o the compressor and burstgaskets in the compressor valve system.Coking occurs mainly as a result o moisture inthe rerigeration system. In high temperatures,the presence o moisture also causes copperplating on valve seats. The burst gaskets are theresult o an excessive condensing pressure andexcessively high short-lived pressure peaks >60bar (liquid hammer).

We recommend the installation o good qualitylter driers. I the lter material is o poor quality,wear will occur which will not only cause thepartial blockage o capillary tube and the lter inthe thermostatic expansion valve, but it will alsodamage the compressor (mainly seizure).

In general, commercial rerigeration systemsmust be equippd with lters having a solid core,e.g. type DML. See also the chapter Filter driers &sight glasses.

The lter drier must be replaced ater everyrepair. When replacing a pencil drier (oten usedin rerigerators) care must be taken to ensurethat the lter material used is suitable or thererigerant and that there is sufcient material orthe application.

Poorly soldered joints can also cause systemblockage. Making good soldered joints isconditional on using the correct soldering metalcontaining the correct percentage o silver.

The use o ux should be limited and kept to asminimum as possible.

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Trouble

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2.5

2.6

2.7

2.8

Poorly soldered joints can also cause leakageand thereby coking. In a rerigeration circuit theproportion o non-condensible gases shouldbe kept below 2%, otherwise the pressure levelwill rise. The main purpose o evacuation is

to remove non-condensible gases beore thererigerant is charged. This also produces a dryingeect in the rerigeration system. Evacuationcan be perormed either rom both dischargeand suction sides, or rom the suction sideonly. Evacuation rom both sides gives the bestvacuum. Evacuation rom the suction side onlymakes it difcult to obtain sufcient vacuumon the discharge side. Thereore, with one-sided evacuation, intermediate ushing withdry Nitrogen is recommended until pressureequalisation is achieved.

Dirt on the condenser and a an motor deect cancause excessive condensing pressure and thereby

reduced rerigeration capacity. In such cases thebuilt-in high-pressure switch provides overloadprotection on the condenser side.Note: The built-in motor protector does notgive the compressor optimum protection ithe condensing pressure rises as a result o aan motor drop-out. The temperature o themotor protector does not rise quickly enoughto ensure the protector cutout. This also applieswhen the rerigerant quantity is greater than canbe accommodated in the ree volume on thedischarge side.

It is important to determine the quantity orerigerant precisely especially in capillary tubesystems. The guidelines are that the temperatureon the evaporator inlet must, as ar as possible,be the same as the temperature at its outlet, andthat as much superheating as possible must beobtained between the evaporator outlet and thecompressor inlet. (The inlet temperature on thecompressor must be about 10 K less than thecondensing temperature).

Overcharging o a rerigeration system equippedwith a thermostatic expansion valve becomescritical when the charging quantity in liquidcondition is greater than can be accommodatedby the ree volume in the receiver, i.e. thecondenser area is reduced and the condensingpressure rises.

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2.9

2.10

It is very seldom that there is too little rerigerantin a system, unless leakage occurs. Irregular icingon the evaporator is oten a sign o insufcientrerigerant. This irregular icing does not onlyreduce the rerigeration output, it can also give

problems in evaporator derosting because thederost thermostat sensor does not register thepresence o ice. Thereore, precise determinationo the rerigerant charge is recommended as away o making sure that ice on the evaporator isevenly distributed.

The optimum system efciency is obtained whena heat exchanger is tted to ensure subcooling:about 5 K in systems with thermostatic expansionvalve and about 3 K in systems with capillarytube. In systems with a thermostatic expansionvalve the suction and liquid lines must be

soldered together over a distance o 0.5 to 1.0 m.In capillary tube systems the capillary tube andsuction line must be soldered together or 1.5 to2.0 m.

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Trouble

shooting


3.0Power consumptiontoo high

3.1

3.2

3.3

Compressor Signs o compressor wear

Motor deect

Reduced rerigeration capacity

Compressor cooling

Pressure irregularity Blockage

Non-condensible gasesMoisture

Dirt

Fan deect

Overload Application limits exceeded

Voltage/requency


Temperature

Rerigerant type

Pressure irregularity and overload oten causecompressor deects that show themselves in theorm o increased power consumption. Reer tothe previous pages or inormation on problems

with pressure irregularity and compressoroverload seen rom the system side.Excessive evaporating and condensing pressurescause compressor motor overload which leads toincreased power consumption. This problem alsoarises i the compressor is not sufciently cooled,or i extreme overvoltage occurs. Undervoltageis not normally a problem in Western Europebecause here the voltage rarely drops below198 V.

Constant overload will give signs o wear

in compressor bearings and valve systems.Overload that causes requent winding protectorcutouts can also produce an increased number oelectrical drop-outs.In cases where the application limits areexceeded, the system must be adapted. Forexample, by the use o a thermostatic expansionvalve with an MOP that will limit the evaporatingpressure, a pressure regulator, or a condensingpressure regulator. See also the chapterThermostatic expansion valves and the chapterPressure regulators.

Static cooling (in certain circumstances an

oil cooler) is sufcient or most householdrerigeration appliances, provided that theclearances specied by the manuacturer aremaintained, especially where a built-in applianceis concerned.

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3.5

3.4 Commercial equipment should be an-cooled.The normal recommended air velocity acrosscondenser and compressor is 3 m/s.

A urther recommendation is regular service onthe rerigeration system, including cleaning othe condenser.

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Trouble

shooting


4.2

4.1

4.0Noise

4.3

Compressor Pressure circuit

Oil level

Clearance: piston/cylinder

Valve system

Fan Deormed an blades

Bearing wearBaseplate

Valves Whistling rom thermostatic expansion valves

Chatter rom solenoid and check valves

System noise Liquid noise

(mainly in evaporator)

Installation Piping

Compressor, an and condenser brackets

Danoss compressors and condensing unitsdo not normally give rise to complaints about

noise. The noise level o compressors and, aboveall, ans is well in agreement with the demandsmade by the market. I occasional complaints arereceived, they usually arise rom installation orsystem errors.

The rare noise problems that do occur are mostlybecause o production aults, e.g. discharge linetouching the compressor housing, oil level toohigh/low, too much clearance between pistonand cylinder, aulty assembly o the valve system.Such noise is easy to diagnose with a screwdriverused as a "stethoscope".

System noise is a critical actor in householdappliances. Here, liquid noise at the evaporatorinlet is characteristic. On the system side it isdifcult to remedy this problem because whatis involved is a mass produced equipment. Ithe lter is mounted vertically, it might help tomount it horizontally instead. However, it shouldbe remembered that noise can be amplied bystructure, e.g. with a built-in appliance. In such asituation, the manuacturer should be contacted.

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4.5

4.6

4.7

To prevent noise transer, pipework should notbe allowed to touch the compressor, the heatexchanger or the side walls.When installing a compressor, the ttings andgrommet sleeves supplied must be used to avoid

the rubber pads being compressed so much thatthey lose their noise-suppression properties.

Fans are used mostly in commercial rerigerationsystems. Noise will be generated i the an bladesbecome deormed or touch the heat exchanger

ns. Worn bearings also produce a great deal onoise. Additionally, the an unit must be rmlysecured so that it does not move in relationto its mounting bracket. Normally, ans have ahigher noise level than compressors. In somecircumstances, it is possible to reduce the noiselevel by installing a smaller an motor, but thiscan only be recommended when the condenserarea is over-sized.

I the noise comes rom the valves, the causeis usually incorrect sizing. Solenoid and check

valves must never be sized to suit the pipeconnections, but in accordance with the kv value.

This ensures the min. pressure drop necessary toopen the valve and keep it open without valve"chatter". Another phenomenon is "whistling"in thermostatic expansion valves. Here a checkshould be made to ensure that the size o theorice corresponds to the system characteristicsand that above all there is sufcient liquid sub-cooling ahead o the expansion valve [approx. 5 K].

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103 FN Troubleshooting