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1 2010 Emerson Climate Technologies

Printed in the U.S.A.

AE4-1240 R7

Application Engineering

B U L L E T I N

Application of Model BR Compressor

AE4-1240 R7 June 1988Reformatted October 2010


B U L L E T I N

Since the introduction of the Copelaweld "BR" motor-compressor family, major improvements in design andconstruction have been incorporated which greatlyexpand the application range of these models. Thedouble Scotch yoke design has proven its ruggeddurability under severe operating conditions.

Figures 1, 2, and 3 help visualize the internal workingparts of the compressor and their interrelated movementwhen the motor is energized. Power is transmittedfrom an electric motor by a revolving crankshaft of

conventional design, with offset throws to create acircular driving force.

Figure 1 illustrates the yoke and piston assembly.Two opposing pistons are mounted rigidly on a yoke.The yoke is constructed of high strength aluminumwith steel plates on the inner surfaces for a durablebearing surface.

The slide block shown in Figure 2fits inside the yoke andis designed to slide smoothly back and forth, providing

the means of converting the rotating movement of thecrankshaft to the reciprocating movement of the pistons.The offset throws of the crankshaft fits through the holein the slide block.

Figure 3 illustrates a complete compression cycle withthe double Scotch yoke mechanism.

In position A, #1 piston is at the bottom of its suctionstroke, while #2 piston is on top dead center at the endof its compression stroke.

In position B, the crankshaft has rotated 90. The #1piston is now midway in its compression stroke, while#2 piston is midway in a suction stroke. Note that theslide block has moved to the left to compensate for therotary movement of the crankshaft, while the yoke andpiston assembly moves rigidly as shown.

In position C, the crankshaft has now rotated 180 fromits original position. The slide block has returned to thecenter of the yoke. The #1 piston has completed itscompression stroke while #2 piston has completed itssuction stroke.

In position D, the crankshaft has rotated 270 from itsoriginal position or 3/4 of one revolution. The slide blockhas moved to the right, #1 piston is now on its suctionstroke, while #2 piston is midway in its discharge stroke.

When the crankshaft has completed one revolution,it will again return to position A, and the cycle will berepeated. During the cycle, the slide block moves in fourdirections in one plane, while the movement of the yokeand piston assembly is two directional only.

Figure 1

Yoke and Piston Assembly

Figure 2

Slide Block

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oil level. This can result in oil slugging and valve platedamage.

In order to provide a means of checking the oil level

and removing excess oil from the system, a Schradertype valve at the normal oil level is provided on "BR"compressors. The Schrader valve should dischargerefrigerant vapor with a proper oil charge in thecompressor. If the Schrader valve discharges oil (liquidor foam), this indicates an excessive oil charge, and oilshould be removed through the valve until it dischargesvapor.

Application

All "BR" compressors include as standard equipmenta bellyband type crankcase heater installed at oil levelon the compressor shell. This heater should be located1-1/4 to 2-1/2 inches from the top of the mounting foot.

Field experience indicates that as the refrigerant chargein the system increases, the potential mechanicalstress level from liquid flooding or liquid migration alsoincreases rapidly. Furthermore, if the evaporator candrain liquid by gravity to the compressor, the crankcaseheater may be overpowered by refrigerant recondensingand running back into the compressor as fast as thecrankcase heater vaporizes it.While a compressor can digest small amounts of

The BR family is a four-cylinder compressor with twodouble-ended Scotch yoke assemblies mounted oneabove the other. In the compressor, the crankshaft isvertical and each Scotch yoke assembly is offset 180,

so the cylinders are located 90 apart. As a result, thecompressor is inherently well balanced and smoothrunning.

Motor Protection

BR*2 models all have internal inherent motorprotection. BR*1 models had pilot circuit solid stateprotection, manufactured by either Robertshaw orTexas Instruments, which are not interchangeable.The wiring diagrams for BRK1 compressors with TexasInstruments protection modules are shown in Figure4. The wiring diagram for compressors with internalinherent protection is shown in Figure 5.

Lubrication

BR compressors are furnished with either white or 3GSoil, depending upon OEM requirements. White oil and3GS are fully compatible and may be mixed in the field.

On applications where a service replacementcompressor has been installed, it is quite possible thatthere may be residual oil in the system, with the resultthat, after a short period of operation, the replacementcompressor can be operating with an excessively high

Figure 3

Scotch Yoke Compression Cycle

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compressor compartments can cause excessively highoil temperatures.

"BR" models are suitable for both air conditioning

and heat pump applications with refrigerant R-22.The published operating curves indicate the limits forspecified evaporating and condensing temperatures.

The compressor cut-off points on the operating curvesare established at conditions when discharge valvetemperatures reach a level where oil coking can occur.Prolonged operation at or near cut-off points canhave a detrimental effect on compressor life and forcompressors which must operate continuously with lowevaporating temperatures R-502 may be a preferablerefrigerant because of its lower discharge temperatures.

For heat pump applications the general recommendationsas set forth in AE17-1243 apply, including a liquidflooding refrigerant control device, a suction accumu-lator, and continuous compressor operation at lowambients. In order to avoid compressor overheating onair-to-air heat pump applications, the expansion devicemust flood sufficient liquid to cool the compressor, andto avoid liquid refrigerant damage, the accumulatormust limit the amount of liquid refrigerant that reachesthe crankcase. The most critical operating conditionsare operation at low outdoor ambients in the heatingmode, or operation with the outdoor coil iced up, whichresults in high compression ratio.

Recommended Test Procedure for Air-to-Air HeatPumps

In order to determine if the "BR" compressor can bemaintained within safe temperature limits on an air-to-air heat pump, the following test procedure should befollowed.

Mount the unit in a suitable test room and disconnectthe defrost control. Maintain the indoor room at 70Fand lower the temperature of the outdoor room to as lowa temperature as possible. Spray the outdoor coil withwater to frost it completely, and recirculate the airflowon the outdoor coil to drive the evaporator temperatureto -20F or below. Operate the unit several hours at

this condition.

If the compressor sump temperature falls below 35F,too much liquid refrigerant is reaching the compressorcrankcase, and an accumulator with a smaller orificeshould be used.

If the discharge temperature exceeds 250F, thecompressor is not being adequately cooled, andeither the liquid expansion device or the orifice in the

liquid refrigerant on an occasional basis, frequentliquid induced stress can cause mechanical damage.Since the BR line is in the higher horse power rangefor welded compressors, by the mere fact of its size

and capacity, system induced problems tend to moresevere. Therefore, in the best interest of both EmersonClimate Technologies and our customers, more stringentapplication requirements have been established for"BR" compressors compared to smaller hermeticcompressors.

Since there is no direct factory control of condensingunit applications, a suction accumulator is mandatoryon any remote condensing units utilizing the BRH andBRK models. A suction accumulator is mandatory forall BR models in all systems if the system refrigerantcharge exceeds 16 pounds. Packaged computerroom air conditioners require an accumulator under allconditions due to poten tial rapid cycling operation andclose coupled components. If the system refrigerantcharge on any type of system exceeds 30 pounds, apumpdown system type of control should be used inaddition to the accumulator. Failure to follow Emersonspecifications in this regard may adversely affectcompressor replacement at no charge should a failureoccur during the warranty period.

There is no internal pressure relief valve in BRcompressors and a high pressure control is requiredfor all applications. On compressors with Rotalockspud connections, a port is provided on the spud for ahigh pressure control connection. On compressors withstub tubes for brazed connections, no port is providedon the compressor and the connection must be madeexternally to the hot gas discharge line. Abnormally highdischarge pressure usually indicates a system problemwhich needs to be corrected. Automatic reset highpressure controls provide marginal protection at best,and a manual reset high pressure control is stronglyrecommended for proper compressor protection.

For loss of charge protection, a low pressure controlis required for all applications. For air conditioningapplications a minimum setting of 30 psig isrecommended while 10 psig is recommended for heat

pumps. For heat pump applications a high dischargetemperature cut-off on the discharge line is required toprevent overheating under loss of charge conditions.The cut-out temperature should be 275F.

The "BR" compressor requires air flow over thecompressor shell for proper cooling. Ventilation ofthe compartment in which the compressor is locatedby airflowing to the condenser fan will be ade quateprovided vents are located so that air flows freelyaround the base of the compressor. Tightly insulated

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accumulator must be enlarged to allow additional liquidrefrigerant flooding to cool the compressor.

The use of refrigerant R-502 is another alternativewhich will result in a significant reduction in dischargetemperatures.

Replacement of BR*1 Compressors with BR*2Models

Aside from the electrical terminal box, BR*2 modelswith inherent protection are physically identical to BR*1models with solid state module protection. Therefore,the only installation problem when changing models isa minor wiring modification described below:

When installing BR*2 models in a system originallycontaining BR*1 models:

1. Remove the wiring leads originally run from theline or transformer to the line terminals (T1-T2)on the solid state module.

2. Either jumper the leads originally run to thecontrol terminals (M1-M2) on the solid statemodule, or remove the leads to M1-M2 and rerunthe control wiring directly from the control to thecontactor coil.

3. The only wiring connections to the BR*2 modelsare the three power leads.

4. See Figures 4 and 5.

BR Mounting Assembly

The mounting assembly for the BR compressor is shownin Figure 6, along with part numbers for the mountingcomponents which Emerson supplies.

Figure 4

Solid State Protection, TSC, TSD, TSE

BRK1 Model

Figure 5

Internal Inherent Motor Protection BRE2, BRG2,

BRH2, BRK2 Models

Figure 6

BR Mounting Assembly

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