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1 2008 Emerson Climate Technologies

Printed in the U.S.A.

AE4-1287 R4

Application Engineering

B U L L E T I N

COPELAND DISCUS DEMAND COOLING

AE4-1287 R4 April 2009


B U L L E T I N

Introduction

HCFC-22, when used in a properly designed andcontrolled refrigeration system, is a realistic lowtemperature refrigerant alternative to CFC-502, whichhas been phased out due to its high ozone depletionpotential. However, experience has shown thatHCFC-22 can present problems as a low temperaturerefrigerant because under some conditions the internalcompressor discharge temperature exceeds the safetemperature limit for long term stability of refrigerationoil. Other refrigerants such as HFC-407A and HFC-407Calso have these characteristics.

The Demand Coolingsystem (seeFigure 1) uses modernelectronics to provide a reliable cost effective solution tothis problem. It is required for all single stage HCFC-22,HFC-407A and HFC-407C applications with saturatedsuction temperatures below -10F.

Demand Cooling is compatible with single (conventional)units as well as parallel racks.

The Demand Cooling module uses the signal ofa discharge head temperature sensor to monitordischarge gas temperature. If a critical temperatureis reached, the module energizes a long life injection

valve which meters a controlled amount of saturatedrefrigerant into the compressor suction cavity to coolthe suction gas. This process controls the discharge

temperature to a safe level. If, for some reason, thedischarge temperature rises above a preset maximumlevel, the Demand Cooling module will turn thecompressor off (requiring a manual reset) and actuateits alarm contact. To minimize the amount of refrigerantwhich must be injected, the suction gas coolingprocess is performed after the gas has passed aroundand through the motor.

Injection valve orifices have been carefully chosenfor each body style to be large enough to provide the

necessary cooling when required but not so largethat dangerous amounts of liquid are injected, or thatexcessive system pressure fluctuation occurs duringinjection valve cycling. Normally, pressure fluctua-tions are no greater than 1 to 2 psi. It is important touse the correct valve for each compressor bodystyle.

Performance data for Demand Cooling compressorsincludes the effects of injection when it isrequired. The approximate conditions where injectionoccurs are shown in Figure 2 and 3. At the conditionswhere Demand Cooling is operating, the performancevalues are time averages of the instantaneous values,

since smallfluctuations in suction and dischargeconditions occur as the Demand Cooling injection

valve cycles.

Figure 1Demand Cooling System

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90

100

110

120

130

140

perature(F) 65F Return Gas Demand

Cooling Injecon Line

40F Return Gas DemandCoolingInjeconLine

DemandCooling

Required*

30

40

50

60

70

80

-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5

CondensingTe

Evaporang Temperature (F)

*If Liquid Injecon Is Not Installed, Recommend 265F MAX Discharge Line Temp. Limit

Figure 2Low Temperature Operating Envelope with Demand Cooling for R-407A and R-407C (without Head Fan*)

* If using with a head fan with a HFC-407A or HFC-407C system, assume the 40F return gas and 65Freturn gas injection lines can each be shifted up about 5F.

90

100

110

120

130

140

mperature(F)

Demand Cooling

Required*

30

40

50

60

70

80

-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5

CondensingT

Evaporang Temperature (F)

e urn as eman

Cooling Injecon Line

*If Liquid Injecon Is Not Installed, Recommend 265F MAX Discharge Line Temp. Limit

Figure 3Low Temperature Operating Envelope for R-22 at 65F Return Gas (with Head Fan)

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DEMAND-COOLING

CONTROL

MODULE

TO CONTROL

CIRCUIT

REFRIGERANT INJECTION LINE

MANUAL SHUTOFF

VALVE

INJECTION

LINE FILTER

DEMAND COOLING

SENSOR AND

SENSOR LINES

RECEIVER

LIQUID LINE

FILTER DRIER

COMPRESSOR

EVAPORATOR

INJECTION

SOLENOID

VALVE

SIGHT GLASS

SUCTION

LINE FILTER

ACCUMULATOR

CONDENSER

M

L

AS

TXV

INJECTION VALVE

ELECTRICAL

CONTROL LINE

While the refrigerant injection concept has beenwidely recognized for some time, its application hasnot been widely used since the early 1960s becauseof the widespread availability of CFC-502, reductionof capacity and efficiency, and poor reliability of injectionsystems.

The Demand Cooling system addresses thecapacity and efficiency issues by limiting injectionto those times when it is required to control dischargetemperatures to safe levels. For most applications this willonly be during periods of high condensing temperatures,high return gas temperatures, or abnormally lowsuction pressure. The Demand Cooling systemhas been designed to meet the same high reliabilitystandards as Discus compressors.

In most cases, with floating head systems wherecondensing temperatures are low during most of theyear, Demand Cooling will operate primarily as acompressor protection control much as the oil failurecontrol protects the compressor during periods of lowoil pressure. Demand Cooling will be called to operateonly during those periods when condensingtemperatures and return gas temperatures are highor in periods where a system failure (such as an icedevaporator, an expansion valve which does not controlsuperheat, blocked condenser, or a failed condenser

fan) raises condensing temperatures or return gastemperatures to abnormally high levels or lowers suctionpressure to abnormally low levels.

Operating Range

Demand Cooling is designed to protect thecompressor from high discharge temperatures overthe evaporating and condensing temperature rangesshown previously in Figure 2 and Figure 3 for bothHFC-407A/ HFC-407C and HCFC-22. For informationon head fan requirements or other return gas conditions,contact your Application Engineer.

Demand Cooling System Design

When Demand Cooling operates, it divertsrefrigeration capacity in the form of injected saturated

refrigerant from the evaporator to the compressor(See Figure 4 for a typical single system schematic).The effect of this diversion on evaporator capacityis minimal because the diverted capacity is used tocool the gas entering the compressor. As the gas iscooled, it naturally becomes more dense, increasingthe mass flow through the compressor, which partlycompensates for the capacity diverted from theevaporator.

Figure 4Demand Cooling System Diagram

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If there is substantial heat gain along the suctionline, injection may result in a substantial loss inevaporator capacity during Demand Coolingoperation.In order to minimize this loss, good practice indicatesDemand Cooling operation be kept to a minimumthrough proper system design and installation practices.There are three areas which can be addressed tominimize the impact of Demand Cooling operation onperformance.

1. Compressor Return Gas Temperature: Suctionlines should be well insulated to reduce suctionline heat gain. Return gas superheat should be aslow as possible consistent with safe compressoroperation.

2. Condensing Temperatures: It is important whenusing HCFC-22, HFC-407A or HFC-407C as

a low temperature refrigerant that condensingtemperatures be minimized to reduce compressionratios and compressor discharge temperature.

3. Suction pressure: Evaporator design and systemcontrol settings should provide the maximumsuction pressure consistent with the applicationin order to have as low a compression ratio aspossible.

Demand Cooling Compressors

No new compressor models have been introducedfor Demand Cooling. Instead, existing lowtemperature Discus CFC-502 compressors have been

modified for use with HCFC-22, HFC-407A or HFC-407C and Demand Cooling. The modifications are

the addition of an injection port on the compressorbody and a temperature sensor port in the head of thecompressor. The locations of these ports are critical andwere determined through an extensive developmentprogram.

The HCFC-22, HFC-407A and HFC-407C rating dataincludes the effects of Demand Cooling injection whenoperating conditions require it based on 65 F returngas.

Condenser Sizing

Condensers should be sized using conventionalmethods. Demand Cooling has virtually no effect onsystem heat of rejection.

Demand Cooling System Components

The Demand Cooling System (see Figure 1) consistsof: The Demand Cooling Temperature Sensor (TS),The Demand Cooling Module (CM), and the InjectionValve (lV).

The TS uses a precision Negative TemperatureCoefficient (NTC) Thermistor (thermistor resistancedrops on temperature rise) to provide temperaturesignals to the CM.

The IV meters refrigerant flow from the liquid lineto the compressor. The IV solenoid receives on-offsignals from the CM. When compressor cooling isrequired the solenoid is energized and opens the IVorifice to deliver saturated refrigerant to the compressorfor cooling. The valve orifice is carefully sized tomeet the requirements of each body style of Discuscompressors.

The CM has three functional groups:

A. The Input signal and calculator circuitscompare the temperature sensor input signal to an

internal set-point and decide whether to energizethe IV solenoid or, in the case of a problem, theCM alarm relay.

B. The output signal to the IV is controlled byan electronic switch connected to the IVsolenoid so that, when required, refrigerantvapor can be metered to the compressor toprevent compressor overheating. One side of theelectronic switch is connected internally to L1and the other side to output terminal S (seeFigure 6).

C. The alarm signal for local or remote control. The

alarm relay is energized, after a one minute delay,by a continuous, low or high TS temperature signal.An alarm signal can indicate the following:

1. Compressor discharge temperature hasrisen above the level designed to becontrolled by Demand Cooling.

2. A shorted sensor.

3. An open sensor.

In order to avoid nuisance trips, a one minutetime delay is provided before alarm after a continuoushigh or low resistance reading or over temperaturecondition.

The alarm relay uses a single-pole-double-throwcontact. The contact terminals are L, M, andA:

L - Common (to A and M)

L - M - Normally Closed (compressor run. openon alarm)

L - A - Normally Open (alarm signal, close onalarm)

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The Normally Closed (NC) contact of the alarmrelay (L to M) should be wired in the compressorcontactor control circuit so that opening thiscontact removes the compressor from the line andremoves power to the CM. See Figure 5A, B, C, and D.

Figures 5A and B also show a current sensing relay(which must be used with compressors employinginternal overcurrent protection) and Sentronicoil pressure switch. The control circuit is purposelyarranged so that an internal overload protector tripremoves power to both the Sentronic and the Demand

Cooling module. This precaution prevents the oilpressure switch from timing out and the DemandCooling solenoid from injecting when the compressoris not operating.

The alarm relay requires a manual reset in order to call

attention to a system problem.

System Information

1. Demand Cooling is designed to work on allCopeland Discus compressors equipped withinjection ports. A different kit is required for eachcompressor body style and control voltage. SeeTable 2 for a listing of Demand Cooling Kit partnumbers.

2. The system must be clean. A dirty system mayhave foreign material that can lodge in the solenoidorifice. Always install a liquid line filter dryer in

the injection valve inlet line capable of removingparticles as small as 25 microns.

3. Do not use anyfilters containing materials that canleave the filter and possibly clog the IV orifice.

4. The liquid refrigerant supply line must be aminimum of 3/8" and routed so it will not interferewith compressor maintenance. Liquid refrigerantmust have sufficient subcooling at the injectionvalve to prevent flashing upstream of the valve.

5. The liquid refrigerant supply line to the IV must besupported so that it does not place stress on theIV and IV tubing or permit excess vibration. Failure

to make this provision may result in damage to theIV and its tubing and/or refrigerant loss.

6. A head fan must be used to help lower compressordischarge temperatures for compressors usingHCFC-22. Contact your Application Engineer forhead fan requirements with other refrigerants.

7. Return gas temperatures must NOT exceed65F.

8. System designers are advised to review theirdefrost schemes to avoid floodback to thecompressor which may occur at defrost terminationwith HCFC-22, HFC-407A and HFC-407C. Theserefrigerants have a significantly higher heat ofvaporization than does CFC-502, and if the samedesign parameters used with CFC-502 are used,floodback may occur.

Demand Cooling with Discus CompressorUnloading

Demand Cooling has been approved with unloadingfor 4D, 6D and 3D Copeland Discus Digital. DemandCooling has NOT been approved for 3D Moduload.

Note! Intelligent Store Discus with Demand CoolingIs NOT approved at this time.

4D and 6D Unloading with Demand Cooling

Demand Cooling has afixed injection orifice designed forfully loaded Discus compressors. Because an unloadedcompressor has less ability to handle the saturated vaporintroduced to the suction cavity, there can be liquid buildup in the crankcase of the compressor with consequentreduced lubrication and possible slugging.

To prevent excessive liquid introduction the compressorcontrol circuit should be designed to fully load thecompressor whenever Demand Cooling injection isnecessary.

Extending the Life of the Unloader ControlSolenoid

Demand Cooling cycles off and on to maintain dischargetemperatures between 282F and 292F. If thecompressor unloader solenoid is allowed to operate eachDemand Cooling cycle then its life will be shortened.

To extend the life of the compressor unloading solenoid,the compressor control circuit must be designed to firstopen the unloading control circuit, and then hold theunloading circuit open with the compressor loadedfor one minute after injection has stopped.

The Unloader Control Circuit Electronic Timer

The unloader one minute timer is a delay-after-breaktype. This describes a timer whose output contactsswitch immediately with an initiating signal. Only afterthe signal voltage is removed will the timing action begin.

At the end of the timing action, the timer contacts returnto their original positions. If during the timing period theinitiating signal returns, the timer resets and will not begintiming again until the signal is removed.

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CC

L1

L2L3

L1

L2

L

M

L

M

A

A

S

240 2

L1

L2

L3

L1

L2

LMAS

CC

CS

CC

L1

L2

L3

L1

L2

L

M

LM

A

A

S

CS

2402

L1

L2

L

MS

A

L

M A

240

2

L1

L2

WithSe

ntronicOilPressureControl

AndCurrentSensingRelay

LessSentronicOilPressureControl

WithSentronicOilPressureControl

Less

CurrentSensingRelay

With

IsolatedControlContacts

NOTE:Compressorswith

internaloverloadprotection

MUSThavesomemeans,

suchasacurrentsensing

relay,todeenergizethe

DemandCoolingModule

andtheSentronicwhenthe

compressorisnotrunning!

NOTE:Thecontrolcircuit

mustbearrangedsothatthe

DemandCoolingModule

andtheSentronicare

deenergizedwhenthe




DemandCoolingModule

andtheSentronicare

deenergizedwhenthe




DemandCoolingModule

andtheSentronicare

deenergizedwhenthe

compressorisnotrunning!2

40vac

Current

Sensing(CS)

Relay

Compressor

Contactor(CC)

C

ompressor

M

otor

240

vac

Current

Sensing(CS)

Relay

Compressor

Contactor(CC)

C

ompressor

M

otor

Compressor

Contactor(CC)

Comp

ressor

Motor

240

vac

Demand

Cooling

Module

Demand

Cooling

Module

Demand

Cooling

Module

Demand

Cooling

Module

Sentronic

Sentronic

Control

Controls

Controls

Controls

Temp.

Sensor

Temp.

Sensor

Tem

p.

Sensor

Temp.

Sensor

Electronic

Switch

Electronic

Switch

Electronic

Switch

Electronic

Switch

Injection

Solenoid

Injection

Solenoid

Injection

Solenoid

Injection

Solenoid

Sentronic

OilPressure

Control

Figure5A,B,C

,DDemandCoolingWiringSchematic

Figure5A

Figure5C

Figure5B

Figure5D

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The timer used in the unloader control circuit uses anormally closed contact that switches open to deenergizethe unloading solenoid.

Electronic timers are not available with a solid statenormally closed contact, unless they are speciallydesigned. The timer usually energizes the coil of anelectro-mechanical relay.The electro-mechanical relayfurnishes the normally closed contact.

Extending the Life of the Timing Relay

To extend the life of the timing relay, the control circuitshould be designed so both the signals from DemandCooling and the unloading control device must bepresent before the timer operates.

The Sequence of Operation of the Unloader Control(See Figure 6 for circuit schematic)

1. If both unloading and injection signals are present,open the unloading solenoid control circuit to returnthe compressor to its fully loaded condition.

2. When injection stops begin the one minute delaybefore reclosing the unloader control circuit.

3. If the timer times out, reclose the unloader control

circuit.4. If injection begins again during timing, reset the

timer. Go to Step 2 or Step 5.

5. Cycle off fully loaded when the load temperaturesare satisfied.

Timing Control Circuit for Demand Cooling-Unloading Control

This circuit uses a hybrid timer that incorporates statetiming with an electro-mechanical output relay on thesame printed circuit board.

The timer has a normally closed, electro-mechanical

contact (Terminals 2 and 4)

Power supply voltage to the timer is on Terminals 5and 1

Figure 6Demand Cooling 4D and 6D Unloading Timer

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The timer initiate signal is to Terminal 6

One side of the timer power supply (Terminal 1) ispermanently connected to the control circuit power. When

voltage is applied to Terminal 5of the timer is powered,but timing does not start. The unloading pressure switchsignal is used to power the timer so the compressor mustbe unloaded for timer to actuate even though there isa Demand Cooling signal on timer Terminal 6. Thissaves unnecessary timer operations.

When the Demand Cooling signal voltage fromTerminal S is applied to Terminal 6, and the timeris powered, the timer contact (Terminal 2 to 4) isimmediately switched open and the unloading solenoidis deenergized.

The 27,000 Ohm, 3W resistor is used in the circuit to

provide a control path for the timer. This type of resistoris common when an electronic timer is used with highlyinductive loads such as an unloader solenoid.

After Demand Cooling injection stops, and there is nolonger a control signal on timerTerminal 6, timingbegins to return the timer contact to its closed position.Timing continues as long as there is no Demand Coolingsignal returns, the timer is instantly reset and must starttiming over again after the injection signal stops.

At no time after the initial contact switch from closedto open, did the timer contact return to its closedposition during the timing process. The timer contactremains open until the timer times out or the compressorcycles off after load satisfication.

3D Copeland Discus Digital with DemandCooling

Demand Cooling can be used with 3D Discusdigitalcompressors without adding extra unloader controlcircuitry. The Demand Cooling temperature sensingprobe must be installed to replace the temperaturesensing probe that is provided with the DigitalCompressor Controller. The T1 to T2 connection onthe Digital Compressor Controller should be jumperedwith a 5 kOhm 1 Watt resistor.This allows the DemandCooling module to protect against high discharge

temperatures and inject liquid when needed.

Performance Adjustment Factors

Since compressor discharge temperature dependsstrongly on the return gas temperature, the amount

of injection and its effect on evaporator capacity andmass flow will vary somewhat with return gastemperature. The approximate effects of return gastemperature on evaporator capacity and mass flow aretabulated in Tables 3A and 3B for HCFC-22. Thesefactors should be applied to the 65F return gas capacityand mass flow values in the published performancedata sheets.

Performance values for HFC-407A and HFC-407C are

not provided in this bulletin. For actual performance

values refer to the "Online Product Information" at

www.emersonclimate.com. As a general rule of thumb,

Emerson Climate Technologies recommends assuming

that HFC-407A and HFC-407C produces about 10% and

15% less evaporator capacity, respectively than R-22

for low temperature applications.

Demand Cooling Specifications

Demand Cooling is designed to operate andprotect the compressor within the evaporating andcondensing envelope identified in Figure 2. Operatingsetpoints and control actions are listed in Table 1.

Attached is the Demand Cooling DiagnosticTroubleshooting Guide (Form No. 92-91)

See also:

Demand Cooling Installation Instruction Guides

Emerson Climate Technologies Publication Nos.

90-130 for 2D/3D Compressors

90-131 for 4D Compressors

90-133 for 6D Compressors

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Table 1Demand Cooling Operating Setpoints and Control Actions

Table 2Demand Cooling Kit Part Numbers

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Table 3ADemand Cooling Evaporator Capacity Adjustment Factors for HCFC-22

Table 3BDemand Cooling Evaporator Mass Flow Adjustment Factors for HCFC-22

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CopelandDemand CoolingDiagnostics

Demand Cooling Operating Characteristics

The Copeland Demand Cooling control uses aNegative Temperature Coefficient Thermistor (NTC).Incorporated in the Demand Cooling Temperature Sensor(hereafter called sensor), is a compressor dischargetemperature monitor. When the temperature sensedby the NTC Thermistor rises, its resistance falls, andwhen temperature sensed by the thermistor drops, itsresistance increases.The sensor resistance signal is coupled to the DemandCooling Module (hereafter called module). The moduleuses the signal to determine when the compressor

discharge temperature has risen to a point whereDemand Cooling is required. When Demand Coolingis required the module energizes the Demand CoolingInjection Valve (hereafter called injection valve) andthe injection valve injects saturated refrigerant intothe compressor suction cavity until the dischargetemperature drops to an acceptable level.

Whenever the compressor starts and the module firstreceives power, there is a one minute delay duringwhich the Demand Cooling system injects saturatedrefrigerant if it is required, but waits for compressordischarge temperature to stabilize before checking foralarm conditions. After one minute, if the resistance of

the probe is too low (the resistance equivalent of 310F),or too high (the resistance equivalent of 4F) the modulewill trip and deenergize the compressor.

Bench Testing Demand Cooling Components

Bench Check of the Sensor

Required Equipment:

A digital thermometer of +/- 1 % full scale accuracy.The thermometer probe should be checked forcalibration in an ice water bath or compared withanother accurately known temperature source.

A digital ohmmeter capable of +/- 1 % accuracy. The

ohmmeter should be checked for accuracy with aknown resistance value such as a +1 % resistor.

Room temperature should be stable and between 60Fand 110F.

1. Wrap the end of the digital thermometer probeand the metal end of the Demand Cooling sensorprobe together with electrical tape or Velcro. Theend of the probe and the end of the thermometermust touch.

2. Place the wrapped probe-sensor inside aninsulation shield to protect it from air currents. Usea material such as Permagum or piping insulationsuch as ArmafleX. The insulating material shouldbe tightly wrapped around the taped-sensor andthe wrap should be secured with wire or tiewraps ifnecessary. There should be no free air movementover the metal part of the taped-sensor.

3. Connect the digital ohmmeter to the two pins onthe plug of the sensor. Make sure there is a goodconnection. Do not take a sensor resistancemeasurement until there is no change in theohmmeter display.

4. Measure the temperature of the thermometersensor and find the corresponding calculatedsensor resistance value from Table 1. Since thevalues of Table 1 are not continuous, you mayhave to interpolate.

5. The sensor resistance reading should be within+/- 5% of the calculated resistance value of Step 4.

End of Test

Table 1

Appendix

ThermometerTemp. (F)

CalculatedSensor

Resistance(Ohms)

59 141426

60.8 135000

62.6 128907

64.4 123129

66.2 117639

68 112437

69.8 107478

71.6 102762

73.4 98289

75.2 9404177 90000

78.8 86139

80.6 82476

82.4 78984

84.2 75663

ThermometerTemp. (F)

CalculatedSensor

Resistance(Ohms)

86 72504

87.8 69480

89.6 66609

91.4 63864

93.2 61254

95 58770

96.8 56394

98.6 54126

100.4 51966

102.2 49914104 47943

105.8 46053

107.6 44262

109.4 42543

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Bench Check of the Module and Injection Valve

Required equipment:

A controlled voltage source the same as the rating

of the module and the injection valve.

A multimeter.

If the jumper supplied on the sensor plug of themodule is not available you may use a small paperclip for the test.

Before starting the test, make sure you have the correctmodule and injection valve.

1. With the module control voltage disconnected, shortthe module sensor plug female terminals with the

jumper or the paperclip. Press the module resetbutton.

2. Attach the injection valve leads to terminals L2and S of the module. The injection valve shouldbe propped in an upright position.

3. You should read zero ohms between the L and Mterminals of the module. This is the Normally Closed(NC) contact of the Single Pole Double Throw (SPDT)module alarm relay. You should read an open circuitbetween L and A. This is Normally Open (NO)contact of the alarm relay.

4. Energize the module by bringing module ratedvoltage to terminals Ll and L2.

*When the sensor connection at the module is

shorted, a very low resistance is seen by the moduleas a very high temperature, and an injection signalis sent to the injection valve.

5. The injection valve will be energized by the closingof an electronic switch in the module. The controlvoltage to energize the injection valve may bemeasured across module terminals S and L2.

*Because this measurement is made across anelectronic switch some leakage voltage may bemeasured when the switch is deenergized. Thisvoltage is much less than the control voltage whichis measured when the electronic switch is closed.

The injection valve operation may also be checked

by listening to the click heard each time the coilof the injection valve is energized and the injectionvalve solenoid plunger seats itself.

If background noise prevents an audible checkof the injection valve coil and magnant operation,grip the injection valve magnet housing and loosenits housing cover screw until magnet vibration isfelt. This proves solenoid operation. Retighten themagnet housing cover screw after this check.

6. After one minute, the module should trip. The runcontact L to M should open, and the alarm contactL to A should close. Deenergize the module anddisconnect the injection valve. The resistance shouldbe zero ohms between L and A, and between Land M there should be an open circuit.

7. Reset the module. Remove the jumper from themodule probe plug so there is an open circuit atthe plug input.

8. Energize the module.

When the sensor connection to the Demand CoolingModule is opened the very high resistance isinterpreted by the module as a very low temperature.Consequently no injection signal is sent to theinjection valve.

9. The injection valve should be energized. A recheck

of Step 5 will confirm this.10. Refer to the test of Step 6 to check the alarm circuit.

Reset the module after the test. If the module orinjection valve fails any of the checks it should bereplaced.

End of TestInstalled System Checks ofDemand Cooling Components

When the Demand Cooling control injects saturatedrefrigerant into the suction cavity of the compressor,the outlet tube of the injection valve frosts. If themodule sensor connection is opened or shorted while

the module is energized, the module will trip after oneminute of operation and must be reset to continue.Before starting the test, make sure you have thecorrect module and injection valve.

If the Injection Valve is Not Injecting

1. With the system deenergized, disconnect the sensorfrom the module and jumper the terminals of themodule connector. Energize the system so thecompressor is running and the module is activated.The injection valve should begin injecting, and frostshould form on the outlet tube of the injection valve.

If frost forms, go to Step 4 otherwise continue toStep 2.

2. If frost does not form in Step 1, check to see if thereis control voltage on the coil of the injection valve(terminals L2 and S of the module).

*Because this measurement is made across anelectronic switch in the module some leakagevoltage may be measured when the switch isdeenergized. This voltage is much less than thecontrol voltage which is measured when the switch

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is closed. If correct control voltage is not present,replace the module.

3. If correct control voltage is present, make sure there

is a full sight glass of liquid from the receiver at theinjection valve. If there is not a full sight glass ofliquid, the piping from the receiver should be checkedbefore proceeding.

Piping connections and sizes must be chosen toassure a full sight glass of liquid for the injectionvalve during any phase of the refrigeration systemoperation. Piping that is too small, or connectionstaken from the tops of manifolds rather from thebottom may result in a lack of refrigerant availablefor the injection valve just when it needs it most,such as after a defrost.

If a full sight glass is present and frost still does not

form, replace the injection valve.4. With the module sensor connector shorted or

open and the module and compressor running,the module should trip in one minute and stop thecompressor.

If the compressor does not stop, check the controlcircuit wiring to be sure the module is wired to stopthe compressor when the module trips. If the wiringis correct, replace the module.

5. Check the discharge temperature by performingSteps 1-6 of the Injection Valve is Cycling On andOff test.

If the discharge temperature is higher than theallowable Table 2 selection, remove the sensorfrom the compressor and use the Bench Check ofthe Sensor Test to check the probe. Replace thesensor if necessary.

End of Test

If the Injection Valve is Continually Injecting

1. Make sure there is a full sight glass of liquid fromthe receiver. If there is not a full sight glass of liquid,there may not be enough liquid to allow DemandCooling to cycle because it uses all available

liquid to keep the discharge temperature belowa dangerous level. The piping from the receiverto the injection valve should be checked beforeproceeding.

Piping connections and sizes must be chosen toassure a full sight glass of liquid for the injectionvalve during any phase of the refrigeration systemoperation. If the suction pressure rises then go toStep 6.

2. Deenergize the system and disconnect the sensorfrom the module. Energize the system so thecompressor is running. The frosting should stop.

If Step 2 is successful, go to Step 4 otherwisecontinue to Step 3.

3. If frosting does not stop, with the sensordisconnected, deenergize the system. Disconnectthe voltage supply to the injection valve and restartthe compressor. If frosting does not stop, replacethe injection valve. If frosting stops, replace themodule.

4. If frosting stops when the sensor is disconnected,check the system for high suction and/or condensingtemperatures before proceeding. As suction and/ordischarge temperatures rise toward the DemandCooling limits (40 F evaporator temperature, 130F

condensing temperature), Demand Cooling will callfor injection for longer periods of time and mayappear to be continuously injecting. Use Figure 1to check Demand Cooling operating areas. Figure1 shows where injection begins for two return gastemperatures (65F and 20F) for R-22. The arrowsmarked (A) and (B) on the graph show the lowestallowable evaporating temperatures using a givencondensing temperature.

Point (A) shows that with 65F return gas and 110F condensing temperature, the lowest evaporatingtemperature without Demand Cooling injectionis -5F. Point (B) shows that if the return gastemperature can be lowered to -20F, while still at a

condensing temperature of 110F, the evaporatingtemperature may be lowered to -20F withoutDemand Cooling operation.

Your injection point can be approximated bydrawing a line representing your return gastemperature in between and parallel to the tworeturn gas temperatures on the Figure 1 (Area2). The higher your return gas temperature is,the closer it will be to the 65F line. The lower itis, the closer it will be to the 20F line. You canthen draw your own dotted lines representing yourcondensing and evaporating temperatures to see ifyou are in the in a Demand Cooling injection zone.

The higher your condensing temperatures are for agiven evaporating temperature, the more injectionis required until finally Demand Cooling may beenergized constantly.

If the suction and condensing temperatures arelower than, or borderline to the injection areas ofFigure 1 then go to Step 5.

If they are much higher the system should becorrected to lower the temperatures or there may

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be occasional Demand Cooling trips. If loweringsystem temperatures corrects the continuousproblem, the test is ended, if not go to Step 5.

5. Deenergize the refrigeration system. Close thesuction service valve. Turn the system on andpump down the compressor to 2-3 psig. Turnthe system off. Wait one minute. The pumpdownshould hold and the pressure should not rise.

If the suction pressure rises then go to Step 6.If the suction pressure does not rise the sensoris calling for injection when it is not required andshould be replaced.

6. If the suction pressure rises, the suction servicevalve may not be entirely closed, the valve plateor valve plate gasket may have been damaged.Damage to the valve plate or its gasket can cause

discharge gas to be introduced to the suctioncavity, resulting in an artificially high suctiontemperature. The artificial suction temperature,in turn, causes an earlier than required DemandCooling injection.

Replace the compressor valve plate and gasketsif required.

End of Test

If the Injection Valve is Cycling On and Off

When the saturated refrigerant is injected into the

compressor suction cavity it lowers the temperature

sensed by the sensor. The lower temperature in turncauses the injection valve to shutoff. After shutoff the

temperature in the suction cavity rises again until it is high

enough for injection to start. The result of this cycling is

that frost on the injection valve outlet tubing alternately

appears during injection, and then disappears after

injection stops.

1) Measure the room temperature.2) Connect the temperature sensor probe to the

compressor discharge line 6 from the dischargevalve. The probe must be tightly secured to thedischarge line, and must be well insulated so that

moving air will not produce a false reading (a poorlyinsulated probe may cause errors of more than30F!).

3) Using Table 2, check the conditions that are closest

to your system. (The evaporator temperature used forTable 2 was -25F). There may be deviation from thetable due to system variation, however, within 5-10%of the published discharge pressures is acceptable.

Note! Table 2 is for HCFC-22. Emerson Climate

Technologies recommends assuming that HFC-407Aand HFC-407C runs about 10F to 15F cooler perthe approved operating ranges.

4) When operating under published conditions, thedischarge temperature should never be more than280F or less than 200F. If successful, the test isended. Otherwise continue to the next step.

5) If the measured discharge temperature is lower bymore than 10% of the discharge temperature of Table2, perform Steps 5-8 of the If The Injection Valve IsContinually Injecting test.

If the measured discharge temperature is more than280F, replace the sensor.

End of Test

Table 2Compressor

ModelRoom

Temp. (F)CondensingTemp. (F)

DischargeTemp. (F)

2D80 80 250-270

110 110 270-280

3D80 80 240-256

110 110 265-280

4D80 80 230-260

110 110 260-280

6D80 80 250-270

110 110 250-270

Figure 1Demand Cooling Areas of Expected Injection

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AE1287