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1© 2008 Emerson Climate Technologies

Printed in the U.S.A.

AE4-1298 R4

Application Engineering

B U L L E T I N

Extended Medium Temperature R-404A/507Hermetic Compressors and Condensing Units

AE4-1298 R4 December 2008

Application Engineering

B U L L E T I N

New hermetic compressors and condensing unitshave been developed for application with R-404A/507refrigerants (HFCs) suitable for use in MediumTemperature and Extended Medium Temperatureapplications. These compressors are described inEmerson Climate Technologies Form No. 1.303.Condensing unit models are described in Form No.94-36 and 94-40. All of these brochures are availablethrough the Emerson Climate Technologies LiteratureDepartment.

These models have been developed due to the needfor non-ozone depleting hermetic products. It must benoted however, that under low evaporating conditionsthe operating envelope for these models will berestricted, especially in comparison to semi-hermeticcompressors typically used in similar applications.The operating envelope and restrictions are shown inFigures 1 and 2.

For a given saturated suction temperature (SST), themaximum condensing temperature, the maximum returngas temperature and the maximum discharge linetemperature as outlined in Figures 1 and 2 must not beexceeded! Operation beyond these limits will cause highcompression ratios and/or excessive internal compressor temperatures resulting in overheating, connecting rodwear, and shortened compressor life.

If the system design is such that operation within theseguidelines cannot be guaranteed, then the followingadditional controls must be added:

1. Discharge Line Thermostat – Located 6" from thecompressor and set to cut-out the compressor at 250°F maximum

2. Low Pressure Control – Set to cut-out at 12 psigminimum

Superheat Requirements

In order to assure that liquid refrigerant does not returnto the compressor during the running cycle, attentionmust be given to maintaining proper superheat at thecompressor suction inlet. Emerson recommends aminimum of 20°F superheat, measured on the suctionline 6 inches from the suction valve, to prevent refrigerantfloodback.

 Another method to determine if liquid is coming back tothe compressor is to accurately measure the differencein temperature between the compressor oil crankcaseand the return line. If this delta can be kept at a minimumof 50°F, no liquid will be present in the crankcase.

Suction Accumulator Requirements

Through our development testing we have found thecombination of HFC refrigerants and polyol ester oil todevelop significantly higher cylinder pressures during

flooded start conditions. As a result, our maximumcharge limits have been adjusted for these families of compressors as shown in the following table.

Table 1

Model Family Maximum Charge (Lbs)

JS 1.75

RS 3

CSxxK3 4

CSxxK6 6

 Any system that exceeds these charge limits mayrequire a suction accumulator or pumpdown cycle. Thepurpose of these precautions is to prevent damage tothe compressor due to continuous floodback and/or flooded start conditions. An accumulator is an effectivemeasure againstfloodback and provides some protectionagainst flooded starts; however, the pumpdown cycleis the most positive means of preventing flooded startconditions.

Crankcase Heater Requirements

Crankcase heaters are recommended on all outdoor applications or indoor applications if expected to

operate in ambients below 40°F, or any system with anaccumulator. CSxxK3 models will only be supplied witha crankcase heater.

 After extensive reliability testing, all of these products,with the exception of the R series, have been approvedfor both R-507 and R-404A refrigerant. The R series didnot pass our motor start test requirements with R-507and is therefore NOT approved for use with R-507.

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2© 2008 Emerson Climate Technologies

Printed in the U.S.A.

AE4-1298 R4

Application Engineering

B U L L E T I N

APPROVED REFRIGERANTS

Lubricants

HFC refrigerants like R-404A and R-507 requirepolyolester lubricants to provide proper miscibility andlubricity. Emerson has approved only three POE's atthis time:

• Mobil Artic EAL 22CC• ICI Emkarate RL32CF

• Thermal Zone 22CC

Should a system require the addition of lubricant for any reason, only the lubricants specified should beused.

Practical Considerations

The application restrictions imposed on thesemodels will require careful system design. Some

considerations for the designer are:1. Units operating at low evaporator 

temperatures will be susceptible tooverheating with dirty condensers and/or restricted air flow. Large condensers (with lowTD's) should be designed into stsyems usingthese compressors and proper condenser coil maintenance will be more critical.

2. Minimum suction line pressure drops willbe important to maintain SST limits at thecompressor.

3. Traditional superheat settings at the TXV's

may be too high to maintain the return gastemperature limits specified.

4. Suction lines should be well insulated.

5. Suction to liquid heat exchangers may not bedesirable if return gas temperatures specifiedare to be maintained.

Model FamilyApproved Refrigerants

R-507 R-404A

JS X X

RS X

CSxxK3 X X

CSxxK6 X X

CS and RS Operating Envelope JS Operating Envelope

Figure 1 Figure 2