AAON CB-060 User Manual

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CB SERIES

Condensing Units

Installation, Operation

& Maintenance

WARNING

QUALIFIED INSTALLER

Improper installation, adjustment, alteration, service or maintenance can cause property damage, personal injury or loss of life. Startup and service must be performed by a Factory Trained Service Technician. A copy of this IOM should be kept with the unit.

WARNING

FOR YOUR SAFETY

Do not store or use gasoline or other flammable vapors and liquids in the vicinity of this or any other appliance.

WARNING

If the information in this manual is not followed exactly, a fire or explosion may result causing property damage, personal injury or loss of life.

Table of Contents
Safety ..............................................................................................................................................	5
CB Base Model and Features Description ......................................................................................	8
General Description ........................................................................................................................	9
Codes and Ordinances.................................................................................................................	9
Receiving Unit ............................................................................................................................	9
Storage ........................................................................................................................................	9
Direct Expansion (DX) Condensing Units ...............................................................................	10
Wiring Diagrams.......................................................................................................................	10
Installation.....................................................................................................................................	11
Locating Unit ............................................................................................................................	11
Lifting the Unit .........................................................................................................................	12
Electrical ...................................................................................................................................	12
Thermostat ................................................................................................................................	14
Refrigerant Piping.....................................................................................................................	14
General..................................................................................................................................	14
Determining Refrigerant Line Size .......................................................................................	15
Liquid Line Sizing ................................................................................................................	15
Suction Line Sizing...............................................................................................................	16
Hot Gas Bypass Line ............................................................................................................	17
Hot Gas Reheat .....................................................................................................................	18
Predetermined Line Sizes .....................................................................................................	18
Startup ...........................................................................................................................................	21
Compressors..............................................................................................................................	21
Charging Refrigerant & Adjusting Refrigerant Charge............................................................	21
Before Charging....................................................................................................................	21
Checking Liquid Sub-cooling ...............................................................................................	22
Checking Evaporator Superheat ...........................................................................................	22
Adjusting Sub-cooling and Superheat Temperatures ...........................................................	22
Air Flow ....................................................................................................................................	23
Operation.......................................................................................................................................	25
Thermostat Operation ...............................................................................................................	25
Compressor ...............................................................................................................................	25
Variable Capacity Compressor Controller....................................................................................	25
Low Ambient Options...................................................................................................................	28
Maintenance..................................................................................................................................	28
Coils ..........................................................................................................................................	28
E-Coated Coil Cleaning ............................................................................................................	28
DX Cooling...............................................................................................................................	30
Condenser Fan Motor ...............................................................................................................	30
Replacement Parts.....................................................................................................................	30
Warranty, Service, and Parts Department.................................................................................	30
Refrigerant Piping Diagrams ........................................................................................................	31
CB Series Startup Form ................................................................................................................	43
Literature Change History.............................................................................................................	45

Index of Tables and Figures
Tables:
Table 1 - Recommended Elevation Minimums ............................................................................	12
Table 2 - Predetermined Line sizes for CB units with two step compressors and R-410A..........	20
Table 3 - Sub-cooling and Superheat............................................................................................	22
Table 4 - Performance Testing Air Flow Setpoints ......................................................................	23
Table 5 - R-410A Refrigerant Temperature-Pressure Chart.........................................................	24
Table 6 - Demand Signal vs. Compressor Capacity Modulation..................................................	26
Table 7 - Thermistor Temperature vs. Resistance Values ............................................................	27
Figures:
Figure 1 – Condensing Unit Clearances .......................................................................................	11
Figure 2 - Riser height versus total equivalent line length ...........................................................	20
Figure 3 - Variable Capacity Compressor Controller ...................................................................	26
Figure 4 - Compressor Controller Flash Code Details..................................................................	27
Figure 5– A/C only piping, AHU above CU ................................................................................	31
Figure 6 – A/C only piping, AHU below CU ...............................................................................	32
Figure 7 – Modulating hot gas reheat piping, AHU above CU ....................................................	33
Figure 8 – Modulating hot gas reheat piping, AHU below CU ....................................................	34
Figure 9 – Hot gas bypass piping, AHU above CU......................................................................	35
Figure 10 – Hot gas bypass piping, AHU below CU....................................................................	36
Figure 11 – Modulating hot gas reheat with hot gas bypass piping, AHU above CU..................	37
Figure 12 – Modulating hot gas reheat with hot gas bypass piping, AHU below CU..................	38
Figure 13 – Heat pump piping, AHU above CU ..........................................................................	39
Figure 14 – Heat pump piping, AHU below CU ..........................................................................	40
Figure 15 – Heat pump with modulating hot gas reheat piping, AHU above CU ........................	41
Figure 16 – Heat pump with modulating hot gas reheat, AHU below CU ...................................	42
R57611 · Rev. - · 130603
(ACP J00187)

Safety

Attention should be paid to the following statements:

NOTE - Notes are intended to clarify the unit installation, operation and maintenance.

CAUTION - Caution statements are given to prevent actions that may result in equipment damage, property damage, or personal injury.

WARNING - Warning statements are given to prevent actions that could result in equipment damage, property damage, personal injury or death.

DANGER - Danger statements are given to prevent actions that will result in equipment damage, property damage, severe personal injury or death.

WARNING

ELECTRIC SHOCK, FIRE OR EXPLOSION HAZARD

Failure to follow safety warnings exactly could result in dangerous operation, serious injury, death or property damage.

Improper servicing could result in dangerous operation, serious injury, death or property damage.

Before servicing, disconnect all electrical power to the unit. More than one disconnect may be provided.

When servicing controls, label all wires prior to disconnecting. Reconnect wires correctly.

Verify proper operation after servicing. Secure all doors with key-lock or nut and bolt.

WARNING

Electric shock hazard. Before servicing, disconnect all electrical power to the unit, including remote disconnects, to avoid shock hazard or injury from rotating parts. Follow proper Lockout-Tagout procedures.

WARNING

FIRE, EXPLOSION OR CARBON MONOXIDE POISONING HAZARD

Failure to replace proper controls could result in fire, explosion or carbon monoxide poisoning. Failure to follow safety warnings exactly could result in serious injury, death or property damage. Do not store or use gasoline or other flammable vapors and liquids in the vicinity of this appliance.

WARNING

During installation, testing, servicing and troubleshooting of the equipment it may be necessary to work with live electrical components. Only a qualified licensed electrician or individual properly trained in handling live electrical components shall perform these tasks.

Standard NFPA-70E, an OSHA regulation requiring an Arc Flash Boundary to be field established and marked for identification of where appropriate Personal Protective Equipment (PPE) be worn, should be followed.

WARNING

GROUNDING REQUIRED

All field installed wiring must be completed by qualified personnel. Field installed wiring must comply with NEC/CEC, local and state electrical code requirements. Failure to follow code requirements could result in serious injury or death. Provide proper unit ground in accordance with these code requirements.

WARNING

ROTATING COMPONENTS

Unit contains fans with moving parts that can cause serious injury. Do not open door containing fans until the power to the unit has been disconnected and fan has stopped rotating.

WARNING

UNIT HANDLING

To prevent injury or death lifting equipment capacity shall exceed unit weight by an adequate safety factor. Always test-lift unit not more than 24 inches high to verify proper center of gravity lift point to avoid unit damage, injury or death.

CAUTION

Rotation must be checked on all MOTORS AND COMPRESSORS of 3 phase units at startup by a qualified service technician. Scroll compressors are directional and can be damaged if rotated in the wrong direction. Compressor rotation must be checked using suction and discharge gauges. Fan motor rotation should be checked for proper operation. Alterations should only be made at the unit power connection

CAUTION

Compartments containing hazardous voltage or rotating parts are equipped with a panel requiring tooled access. Always re-install screws on the panel after installation or service is completed.

WARNING

Do not work in a closed area where refrigerant or nitrogen gases may be leaking. A sufficient quantity of vapors may be present and cause injury or death.

CAUTION

Do not clean DX refrigerant coils with hot water or steam. The use of hot water or steam on refrigerant coils will cause high pressure inside the coil tubing and damage to the coil.

CAUTION

To prevent damage to the unit, do not use acidic chemical coil cleaners. Do not use alkaline chemical coil cleaners with a pH value greater than 8.5, after mixing, without first using an aluminum corrosion inhibitor in the cleaning solution.

WARNING

Some chemical coil cleaning compounds are caustic or toxic. Use these substances only in accordance with the manufacturer’s usage instructions. Failure to follow instructions may result in equipment damage, injury or death.

WARNING

Do not use oxygen, acetylene or air in place of refrigerant and dry nitrogen for leak testing. A violent explosion may result causing injury or death.

WARNING

COMPRESSOR CYCLING

5 MINUTE MINIMUM OFF TIME To prevent motor overheating compressors must cycle off for a minimum of 5 minutes.

5 MINUTE MINIMUM ON TIME

To maintain the proper oil level compressors must cycle on for a minimum of 5 minutes.

The cycle rate must not exceed 6 starts per hour.

1.Startup and service must be performed by a Factory Trained Service Technician.

2.The unit is for outdoor use only. See General Information section for more unit information.

3.Every unit has a unique equipment nameplate with electrical, operational and unit clearance specifications. Always refer to the unit nameplate for specific ratings unique to the model you have purchased.

4.READ THE ENTIRE INSTALLATION, OPERATION AND MAINTENANCE MANUAL. OTHER IMPORTANT SAFETY PRECAUTIONS ARE PROVIDED THROUGHOUT THIS MANUAL.

5.Keep this manual and all literature safeguarded near or on the unit.

CB Base Model and Features Description


				Model/Feature Number
CB	-	B	- 060 -	3	-	B	-	1	: A	D	0	0	0	A	0
Series and		Design	Unit			Compressor		Number
Series and		Design	Unit	Voltage		Compressor		of	1	2	3	4	5	6	7
Generation		Sequence	Size	Voltage		Type		of	1	2	3	4	5	6	7
Generation		Sequence	Size			Type		Circuits
								Circuits

BASE MODEL

SERIES AND GENERATION

REVISION

B = Design Sequence

UNIT SIZE

024 = 24 MBH - 2 Ton - Vertical Discharge 036 = 36 MBH - 3 Ton - Vertical Discharge 048 = 48 MBH - 4 Ton - Vertical Discharge 060 = 60 MBH - 5 Ton - Vertical Discharge

VOLTAGE

1 = 230V/1Φ/60Hz

2 = 230V/3Φ/60Hz

3 = 460V/3Φ/60Hz

4 = 575V/3Φ/60Hz

8 = 208V/3Φ/60Hz

9 = 208V/1Φ/60Hz

COMPRESSOR TYPE

B = R-410A Two Step Scroll Compressor

D = R-410A Variable Capacity Scroll Compressor

F = R-410A Two Step Scroll Compressor with Sound Blanket

H = R-410A Variable Capacity Scroll Compressor with Sound Blanket

NUMBER OF CIRCUITS

1 = One Circuit

FEATURE 2: REFRIGERATION

OPTIONS

0 = Standard - Split System Air Conditioner

A = External Hot Gas Bypass

B = Split System Heat Pump

D = Modulating Hot Gas Reheat

F = Options A + D

G = Options B + D

FEATURE 3: CONTROLS

0 = Standard - Terminal Block

A = Suction Pressure Transducer (F1Wattmaster Reheat)

H = Control Circuit Transformer

J = Variable Capacity Compressor Integrated Controls

S = Suction Pressure Transducer (Not F1 - Wattmaster Controls)

T = Control Circuit Transformer w/ Suction Pressure Transducer

W = Wattmaster CB/F1 Controller

FEATURE 4: COIL PROTECTION

0 = Standard

A = Polymer E-Coated Coil

FEATURE 5: CABINET OPTIONS

0 = Standard – Louvered Panels

A = Wire Grille

D = Corrosion Protection Paint

G = Options A + D

FEATURE 1: AMBIENT CONTROL

0 = Standard (55°F Ambient)

B = Adjustable Fan Cycling (35°F Ambient)

D = Modulating Fan Pressure Control (35°F

Ambient)

F = Flooded Condenser Ambient Controls +

Option B

G = Flooded Condenser Ambient Controls +

Option D

FEATURE 6: WARRANTY

0 = Standard

A = Second to Fifth Year Extended Compressor Warranty

FEATURE 7: TYPE

0 = Standard

X = Special Pricing Authorization

General Description

AAON® CB Series condensing units have been designed for outdoor installation only. Startup and service must be performed by a Factory Trained Service Technician.

WARNING

Codes and Ordinances

System should be sized in accordance with the American Society of Heating, Refrigeration and Air Conditioning Engineers Handbook.

Installation of CB Series units must conform to the ICC standards of the International Mechanical Code, the International Building Code, and local building, plumbing and waste water codes. All appliances must be electrically grounded in accordance with local codes, or in the absence of local codes, the current National Electric Code, ANSI/NFPA 70 or the current Canadian Electrical Code CSA C22.1.

CAUTION

The Clean Air Act of 1990 bans the intentional venting of refrigerant as of July 1, 1992. Approved methods of recovery, recycling, or reclaiming must be followed.

WARNING

Coils and sheet metal surfaces present sharp edges and care must be taken when working with equipment.

WARNING

Failure to observe the following instructions will result in premature failure of your system and possible voiding of the warranty.

Receiving Unit

When received, the unit should be checked for damage that might have occurred in transit. If damage is found it should be noted on the carrier’s Freight Bill. A request for inspection by carrier’s agent should be made in writing at once.

Nameplate should be checked to ensure the correct model sizes and voltages have been received to match the job requirements.

The warranty card must be completed in full and returned to AAON not more than 3 months after unit is delivered.

Storage

If installation will not occur immediately following delivery, store equipment in a dry protected area away from construction traffic and in the proper orientation as marked on the packaging with all internal packaging in place. Secure all loose-shipped items.

Direct Expansion (DX) Condensing Units

CB Series condensing units are factory assembled and wired, including a full charge of R-410A refrigerant for up to 25 feet of line set. Systems with the modulating hot gas reheat option will require refrigerant to be field added because of the additional refrigerant components and piping associated with the system.

Refrigeration system includes factory provided liquid line filter drier and fully hermetic scroll compressor with a positive pressure forced lubrication system.

CAUTION

CRANKCASE HEATER

OPERATION

Units are equipped with compressor crankcase heaters, which should be energized at least 24 hours prior to cooling operation, to clear any liquid refrigerant from the compressors.

Never cut off the main power supply to the unit, except for servicing, emergency, or complete shutdown of the unit. When power is cut off from the unit, compressors using crankcase heaters cannot prevent refrigerant migration. This means the compressor may cool down and liquid refrigerant may accumulate in the compressor. Since the compressor is designed to pump refrigerant gas, damage may occur when power is restored.

If power to the unit must be off for more than an hour, turn the thermostat system switch to “Off”, or turn the unit off at the control panel, and then cut off the main power supply. Leave the unit off until the main power supply has been turned on again

for at least 24 hours. This will give the crankcase heater time to clear any liquid accumulation out of the compressor before it is required to run.

Always control the system from the thermostat, or control panel, never at the main power supply, except for servicing, emergency, or complete shutdown of the unit.

Note: Low Ambient Operation

Units without a low ambient option, such as condenser fan cycling or the 0°F low ambient option, will not operate in the cooling mode of operation properly when the outdoor temperature is below 55°F. Low ambient and/or air handling unit economizer options are recommended if cooling operation below 55°F is expected.

Note: Multiple Systems with Multiple Thermostats

When several heating and cooling split systems are used to condition a space all thermostat switches must be set in either heating mode, cooling mode or off. Do not leave part of the systems switched to the opposite mode. Cooling only systems should be switched off at the thermostat during the heating season.

Wiring Diagrams

Unit specific wiring diagram is laminated in plastic and located inside the controls compartment door.

Installation

AAON equipment has been designed for quick and easy installation.

Locating Unit

CB Series condensing units are designed for outdoor application and placement at ground level or on a rooftop. Units must be placed on a level and solid foundation that can support the unit’s weight.

When rooftop mounted, a steel frame must be provided that will support the unit above the roof itself for load distribution.

When installed at ground level, a one-piece concrete slab or composite condenser pad should be used with footings that extend below the frost line (a substantial base that will not settle). Slab should be surrounded by a graveled area for proper drainage and should not adjoin the building as sound and vibration may be transmitted to the structure. Care must also be taken to protect the coils and fins from damage due to vandalism or other hazards.

Airflow to and from the condensing unit must not be restricted. Coils and fans must be free of any obstructions and debris in order to start and operate properly with a correct amount of airflow. Obstruction to air flow will result in decreased performance and efficiency.

The installation position must provide at least one foot of clearance from the wall for proper air flow to the coils. When multiple units are mounted adjacent to each other, the clearance required between them is three feet.

Service compartment must be accessible for periodic servicing of controls, safety devices, and refrigerant service/shutoff

valves. At least two feet of clearance on this corner of the unit is recommended for service.

Figure 1 – Condensing Unit Clearances

Condensing units should not be installed in an enclosure or pit that is deeper than the height of the unit. When recessed installation is necessary, the clearance to maintain proper airflow is at least three feet.

CB Series condensing units are single circuited with vertical air discharge. There must be no obstruction above the equipment. Do not place the unit under an overhang.

Placement relative to the building air intakes and other structures must be carefully selected. Consider the effects of outdoor fan noise on conditioned space and any adjacent occupied space. It is recommended that the unit be placed so that discharge does not

blow toward windows less than 25 feet away.

Heat pumps require special location consideration in areas where snow accumulation can become an obstruction and in areas with prolonged continuous subfreezing temperatures. Heat pump unit bases are cutout under the outdoor coil to permit drainage of frost accumulation. The unit must be situated to permit free unobstructed drainage of the defrost water and ice. A minimum 3 inches clearance under the outdoor coil is required in the milder climates. In more severe weather locations, it is recommended that the unit be elevated to allow unobstructed drainage and airflow.

Table 1 - Recommended Elevation

Minimums

Design	Suggest Minimum
Temperature	Elevation
+15 F and above	3”
-5 F to +17 F	8”
Below -5 F	12”

Lifting the Unit

CB Series condensing units have channels underneath the base which provide lifting access to the underside of the equipment and allow moving and placement without physical damage.

Dollies and/or carts are recommended to lift and place the unit to prevent damage to the equipment and injury to the installer.

CAUTION

Incorrect lifting can cause damage to the unit.

Care should be taken if using spreader bars, blocking, or other lifting devices to prevent

any damage to the cabinet, coil or condensing fans.

Before lifting unit, be sure that all shipping material has been removed from unit.

Hoist unit to a point directly above the condenser pad, and lower unit into the proper place. Unit may also be positioned with a dolly. When the unit is in place, remove the dolly or lifting device. Make sure the unit is properly seated and level.

Electrical

Verify the unit nameplate agrees with the power supply. Connect power and control field wiring as shown on the unit wiring diagram provided with the unit.

WARNING

Electric shock hazard. Before attempting to perform any installation, service, or maintenance, shut off all electrical power to the unit at the disconnect switches. Unit may have multiple power supplies. Failure to disconnect power could result in dangerous operation, serious injury, death or property damage.

Route power and control wiring through the utility entries on the unit. It is recommended not to run power and control signal wires in the same conduit. If the control wires are to run inside the same conduit, 600 volt wires should be used, or as required by applicable codes.

Size supply conductors based on the unit MCA rating. Supply conductors must be rated a minimum of 75°C.

Protect the branch circuit in accordance with code requirements. The unit must be

electrically grounded in accordance with local codes, or in the absence of local codes, the current National Electric Code, ANSI/NFPA 70 or the current Canadian Electrical Code CSA C22.1.

Note: Units are factory wired for 208V, 230V, 460V or 575V. In some units, the 208V and 230V options may also be provided in single or three phase configurations. The transformer configuration must be checked by a qualified technician prior to startup.

Wire power leads to the unit terminal block or compressor contactor. All wiring beyond this point has been done by the manufacturer and cannot be modified without effecting the unit's agency/safety certification.

All units require field supplied electrical overcurrent and short circuit protection. Device must not be sized larger than the Maximum Overcurrent Protection (MOP) shown on the unit nameplate.

Codes may require a disconnect switch be within sight of the unit.

It is recommended that the field installed overcurrent protection or disconnect switch not be installed on the unit.

Supply voltage must be within the min/max range shown on the unit nameplate. Available short circuit current should not exceed the short circuit current rating (SCCR) shown on the unit nameplate.

CAUTION

Rotation must be checked on all MOTORS AND COMPRESSORS of three phase units. Condenser fan motors should be checked by a qualified service technician at startup and any wiring alteration should only be made at the unit power connection.

Three phase voltage imbalance will cause motor overheating and premature failure. The maximum allowable imbalance is 2.0%.

Voltage imbalance is defined as 100 times the maximum deviation from the average voltage divided by the average voltage.

Example:

(221V+230V+227V)/3 = 226V, then 100*(226V-221V)/226V = 2.2%, which exceeds the allowable imbalance.

Check voltage imbalance at the unit disconnect switch and at the compressor terminal. Contact your local power company for line voltage corrections.

Installing contractor must check for proper motor rotation and check blower motor amperage listed on the motor nameplate is not exceeded.

CAUTION

Three phase voltage imbalance will cause motor overheating and premature failure.

CAUTION

Scroll compressors are directional and will be damaged by operation in the wrong direction. Low pressure switches on compressors have been disconnected after factory testing. Rotation should be checked by a qualified service technician at startup using suction and discharge pressure gauges and any wiring alteration should only be made at the unit power connection.

Wire control signals to the unit’s low voltage terminal block located in the controls compartment.

If any factory installed wiring must be replaced, use a minimum 105°C type AWM insulated conductors.

Thermostat

If a thermostat is used for unit control, thermostat should be located on an inside wall 4-5 feet above the floor where it will not be subjected to drafts, sun exposure, or heat from electrical fixtures or appliances.

Follow thermostat manufacturer’s instructions for general installation procedure.

Thermostat control wiring size must be large enough to prevent excess voltage drop and ensure proper operation.

All external devices must be powered via a separate external power supply.

Units with the modulating hot gas reheat dehumidification feature must use a humidistat or a thermostat with a normally closed (NC) dehumidification option. The following thermostats have been approved for usage with the dehumidification feature,

Robertshaw® 9825i2 Thermostat

Honeywell VisionPRO® IAQ Thermostat

AAON Mini Controller

Refrigerant Piping

(See back of the manual for refrigerant piping diagrams.)

CAUTION

This section is for information only and is not intended to provide all details required by the designer or installer of the refrigerant piping between the condenser or condensing unit and the air handling unit. AAON is not responsible for interconnecting refrigerant piping. Consult ASHRAE Handbook – Refrigeration and ASME Standards.

General

Piping from the condensing unit to the air handler is the responsibility of the installing contractor.

Use only clean type “ACR” copper tubing that has been joined with high temperature brazing alloy.

The pipe or line sizes must be selected to meet the actual installation conditions and not simply based on the connection sizes at the condensing unit or air handler.

All CB Series condensing units are provided with in-line shutoff valves on both the liquid and suction lines. These should remain closed until the system is ready for start-up after piping and vacuuming.

Piping should conform to generally accepted practices and codes.

Upon completion of piping connection, the interconnecting piping and air handler MUST BE evacuated to 500 microns or less; leak checked and charged with refrigerant.

Determining Refrigerant Line Size

CAUTION

Line sizes must be selected to meet actual installation conditions, not simply based on the connection sizes at the condensing unit or air handling unit.

The piping between the condenser and low side must ensure:

1.Minimum pressure drop, and

2.Continuous oil return, and

3.Prevention of liquid refrigerant slugging, or carryover

Minimizing the refrigerant line size is favorable from an economic perspective, reducing installation costs, and reducing the potential for leakage. However, as pipe diameters narrow, pressure-reducing frictional forces increase.

Excessive suction line pressure drop causes loss of compressor capacity and increased power usage resulting in reduced system efficiency. Excessive pressure drops in the liquid line can cause the liquid refrigerant to flash, resulting in faulty Thermal Expansion Valve (TXV) operation and improper system performance. In order to operate efficiently and cost effectively, while avoiding malfunction, refrigeration systems must be designed to minimize both cost and pressure loss.

Equivalent Line Length

All line lengths discussed in this manual, unless specifically stated otherwise, are Equivalent Line Lengths. The frictional pressure drop through valves, fittings, and accessories is determined by establishing the equivalent length of straight pipe of the same diameter. Always use equivalent line lengths when calculating pressure drop.

Special piping provisions must be taken when lines are run underground, up vertical risers, or in excessively long line runs.

Liquid Line Sizing

When sizing the liquid line, it is important to minimize the refrigerant charge to reduce installation costs and improve system reliability. This can be achieved by minimizing the liquid line diameter. However, reducing the pipe diameter will increase the velocity of the liquid refrigerant which increases the frictional pressure drop in the liquid line, and causes other undesirable effects such as noise.

Maintaining the pressure in the liquid line is critical to ensuring sufficient saturation temperature, avoiding flashing upstream of the TXV, and maintaining system efficiency. Pressure losses through the liquid line due to frictional contact, installed accessories, and vertical risers are inevitable. Maintaining adequate subcooling at the condenser to overcome these losses is the only method to ensure that liquid refrigerant reaches the TXV.

Liquid refrigerant traveling upwards in a riser loses head pressure. If the evaporator is below the condenser, and the liquid line does not include risers, the gravitational force will increase the pressure of the liquid refrigerant. This will allow the refrigerant to withstand greater frictional losses without the occurrence of flashing prior to the TXV.

A moisture-indicating sight glass may be field installed in the liquid line to indicate the occurrence of premature flashing or moisture in the line. The sight glass should not be used to determine if the system is properly charged. Use temperature and pressure measurements to determine liquid sub-cooling, not the sight glass.

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