Twist TwistAero PCA090480WH User manual

Property of American Airlines
Maintenance

MODEL PCA090480WH
CHAPTER 2
SERVICE
Table of Contents
March 2013 Table of Contents
Proprietary/Confidential Page 31
© 2013 Twist, Inc.
CHAPTER/
TITLE SECTION PAGE
1: Introduction to Servicing
Owner’s Responsibility.............................................................2 - 1...............33
Preventive Maintenance...........................................................2 - 1...............33
Precautionary Measures .......................................................... 2 - 1...............33
Operator Daily Inspection.........................................................2 - 1...............34
2. Safety Precautions
General Precautions ................................................................2 - 2...............35
Refrigerant Precautions ...........................................................2 - 2...............36
3. Refrigeration Basics and Service
Theory......................................................................................2 - 3...............37
Basic Cycle Explanation................................................2 - 3...............37
Fundamentals ..........................................................................2 - 3...............38
Cleanliness of the Refrigeration System........................ 2 - 3...............38
Oil Refrigerant Mixture...................................................2 - 3...............39
Servicing System and Charging...............................................2 - 3...............40
Gauge Manifold............................................................. 2 - 3...............40
Service Valves............................................................... 2 - 3...............41
Removing Refrigerant....................................................2 - 3...............41
Adding or Removing Oil................................................. 2 - 3...............42
Dealing with Non-Condensable.....................................2 - 3...............43
Refrigerant Leaks.......................................................... 2 - 3...............43
Brazing Refrigerant Lines..............................................2 - 3...............45
Pressure Testing ...........................................................2 - 3...............46
Evacuation.....................................................................2 - 3...............46
Charging........................................................................2 - 3...............47
Property of American Airlines

MODEL PCA090480WH
CHAPTER 2
SERVICE
Table of Contents
Table of Contents March 2013
Page 32 Proprietary/Confidential
© 2013 Twist, Inc.
CHAPTER/
TITLE SECTION PAGE
4. Introduction to Preventive Maintenance Checklists..................2 - 4...............49
5. Preventive Maintenance Quarterly Checklist............................2 - 5...............51
6. Preventive Maintenance Semi- Annual Checklist.....................2 - 6...............53
7. Preventive Maintenance Seasonal Checklist ...........................2 - 7...............55
8. Adjustments
Thermostats .............................................................................2 - 8...............57
Expansion Valve Superheat.....................................................2 - 8...............57
Hot Gas By Pass Valve Adjustment.........................................2 - 8...............58
9. Cleaning and Painting
Filters .......................................................................................2 - 9...............59
Condensers..............................................................................2 - 9...............59
Evaporators and Ducts.............................................................2 - 9...............59
Painting....................................................................................2 - 9...............60
Property of American Airlines

MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 1: Introduction to Servicing
March 2013 2 –1
Proprietary/Confidential Page 33
© 2013 Twist, Inc.
1. Owner’s Responsibility
Ownership of PCA units supplied by Twist, Inc. imposes a duty upon the
Owner to maintain the integrity of the equipment. The objective of periodic
maintenance is to ensure that the units are in the same condition and
configuration as originally supplied by Twist, Inc. and to incorporate any
changes directed by Twist, Inc. to assure the continued service life and safety
of the product.
Maintenance must be performed on a routine basis in accordance with Twist,
Inc.’s recommended preventive maintenance checklists in this chapter to keep
warranty coverage active. Replacement parts must conform to original
equipment specifications.
Modification of the structural, electrical, mechanical, or safety components of
Twist, Inc. Pre-Conditioned Air units must be accomplished in strict
accordance with Twist, Inc.’s specifications if performed by any party other
than Twist, Inc.
Any questions which owners may have relative to the installation,
maintenance, or modification of Twist, Inc.’s products should be referred to
Twist, Inc.
2. Preventive Maintenance
Rigidly adhering to a good program of preventive maintenance will prevent or
reduce failure or the need for corrective maintenance. Preventive
maintenance includes recommended inspections, cleaning of designated
components, and touch-up painting as required. Local conditions will
determine to some degree the exact details of a good preventive maintenance
program.
3. Precautionary Measures
A. Exercise extreme care to insure that all repairs, installations, and
service are of the highest possible quality. Always use the proper tools
for the proper job. Wipe clean all spills, smudges, smear, or dirt
accumulation resulting from preventive maintenance exercises.
Property of American Airlines

MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 1: Introduction to Servicing
2 - 1 March 2013
Page 34 Proprietary/Confidential
© 2013 Twist, Inc.
B. General Considerations
(1) Only trained personnel should work on the Twist Pre-Conditioned
Air unit.
(2) Avoid hurried or careless workmanship.
(3) Schedule work from start to finish without interruption to insure
no steps are overlooked.
(4) Maintenance or work done on the refrigeration systems must be
done only by EPA certified personnel.
4. Operator Daily Inspection
A. The PCA unit operator should visually check to ensure that no loose,
broken, or missing components exist on the unit. When connecting the
supply air hose, ensure that the gasket and clamps is in good physical
condition.
B. After confirming the overall operation of the unit, report any concerns
noted to the maintenance department for repair.
Property of American Airlines

MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 2: Safety Precautions
March 2013 2-2
Proprietary/Confidential Page 35
© 2013 Twist, Inc.
1. General Precautions
WARNING: AVOID CONTACT WITH THE TOP OF A SCROLL
COMPRESSOR. COMPRESSORS BECOME HOT DURING
NORMAL OPERATION.
WARNING: NEVER REMOVE THE COMPRESSOR FROM THE UNIT
WITHOUT REMOVING THE REFRIGERANT PRESSURE
FROM BOTH THE HIGH AND LOW SIDE OF THE SYSTEM.
FAILURE TO DO SO COULD RESULT IN SERIOUS INJURY
OR DEATH, BECAUSE THE ESCAPING PRESSURIZED OIL
AND REFRIGERANT MIXTURE COULD BE IGNITED BY THE
TORCH FLAME.
NOTE: Since the compressor’s scroll flanks may seal the refrigerant
pressure between the high and low sides preventing pressure
equalization through the compressor, remove the refrigerant
charge from both the high and low side of the compressor before
removing the compressor from the system.
Whenever performing work on the unit, turn off the external
power and ensure that all OHSA and/or company safety
requirements are met.
NOTE: The actuator handle mounted on the control panel door is
equipped with provisions for inserting a lockout device when
placed in the OFF position. Always lock the actuator handle "off"
when working on the unit.
If the control panel door is open when the breaker handle
actuator is in the "ON" position, the safety switch will trip the
circuit breaker shunt trip and turn the circuit breaker “OFF”. To
work on the unit with the door open and to turn on the power, the
safety switch can be pulled out to by pass the safety switch. The
power then can be turned on. Use extreme caution when
working on the unit with power ON.
Property of American Airlines

MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 2: Safety Precautions
2-2 March 2013
Page 36 Proprietary/Confidential
© 2013 Twist, Inc.
2. Refrigerant Precautions
A. Eye Hazard - Liquid refrigerant may cause permanent damage if it
comes in direct contact with the eye due to rapid cooling. Whenever
handling refrigerant, wear eye protection and keep face away from
working area.
B. Inhalation - Inhaling high concentration of refrigerant may cause
lightheadedness, narcosis, and possible cardiac arrhythmia. Use
adequate ventilation when handling refrigerants.
C. Toxic Products - Refrigerant by itself is very stable; however, at high
temperatures it may decompose to produce hydrochloric and
hydrofluoric acid. In the presence of open flame, poisonous phosgene
gas is produced.
WARNING: DO NOT BRAZE PIPING, WHICH HAS NOT BEEN PURGED OF
REFRIGERANT. THIS MAY RESULT IN AN EXPLOSION DUE TO
THE OIL/REFRIGERANT MIXTURE.
D. Explosion - Refrigerant by itself is not flammable; however, it is stored
and shipped in pressurized containers. Containers should not be stored
or heated above 125 degrees F, which creates dangerously excessive
pressure in the container and possible explosion.
E. Burns - Body tissue may be damaged by freezing. Avoid contact of
liquid refrigerant with the bare skin since damages similar to burns may
result.
Property of American Airlines

MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 3: Refrigeration Basics and Service
March 2013 2-3
Proprietary/Confidential Page 37
© 2013 Twist, Inc.
1. Theory
The unit employs a vapor-cycle refrigeration system using a scroll type
compressor and refrigerant.
A. Basic cycle explanation
The following is a simplified description of the basic cycle starting at the
compressor:
The compressor receives low-pressure refrigerant vapor and the
compressing process increases both the pressure and the temperature.
The hot, high-pressure gas is forced from the compressor into the
condenser. As the high-pressure gas passes through the finned
condenser coil, it is cooled by outside air moved by motor-driven fans.
As the temperature of the refrigerant vapor reaches the saturation point
corresponding to the pressure in the condenser, the vapor condenses
into a liquid and flows through the thermostatic expansion valve, which
controls the feed of liquid refrigerant to the evaporator. It reduces the
pressure of the refrigerant to the evaporator by means of an orifice.
The reduction of pressure on the liquid refrigerant causes it to boil or
vaporize until the refrigerant is at the saturation point corresponding to
its pressure. As the low temperature refrigerant passes through the
evaporator coil, heat from the air being conditioned flows through the
walls of the evaporator tubing to the refrigerant, causing the boiling
action to continue until the refrigerant is completely vaporized into a
gas.
The expansion valve regulates the flow through the evaporator coil as
necessary to maintain a preset temperature difference (or superheat)
between the evaporating refrigerant and the vapor leaving the
evaporator. As the temperature of the gas leaving the evaporator coil
varies, the expansion valve power element bulb senses its temperature
and acts to modulate the feed through the expansion valve as required.
The refrigerant vapor leaving the evaporator coil travels through the
suction line to the compressor inlet. The refrigeration process starts
over again and continues as long as the compressor is in operation.
Property of American Airlines

MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 3: Refrigeration Basics and Service
2-3 March 2013
Page 38 Proprietary/Confidential
© 2013 Twist, Inc.
2. Fundamentals
A. Cleanliness of the refrigeration system
Absolute cleanliness is necessary in a refrigeration system in order to
insure reliable and trouble-free operation.
Vapor cycle refrigeration systems are vulnerable to attack from two
common contaminants: air and moisture, which are not readily apparent
in the system. If either or both are present in a system, they quickly join
together in attacking the refrigerant and oil, causing corrosion, copper
plating, acid formation, sludge, and other problems. When opening a
refrigeration system for repair or component replacement, take extreme
care to cover or cap open joints to prevent moisture from entering in the
form of vapor, which is always contained in the outside air.
When copper tubing and fittings are brazed, copper oxide may form on
the inside of the tube unless nitrogen or dry CO2is circulated through
the tubing during the brazing operation. This oxide may become a
powdered abrasive, plugging oil passages, scoring bearings, plugging
refrigerant passages, plugging filters, and causing other problems.
Taking reasonable care during service will keep contamination in a
system at a safe and acceptable level.
Important rules of cleanliness:
Keep tubing clean and dry.
Pass an inert gas through the tubing when brazing.
Keep foreign materials out of the system when it is opened.
Thoroughly evacuate the system after any exposure to the
atmosphere.
Any time the system is to be opened, introduce a slightly positive
pressure to prevent air from rushing into the lines.
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MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 3: Refrigeration Basics and Service
March 2013 2-3
Proprietary/Confidential Page 39
© 2013 Twist, Inc.
B. Oil-Refrigerant mixture
In vapor cycle refrigeration systems, oil and refrigerant mix
continuously. Refrigeration oils are soluble in liquid refrigerant, and at
normal room temperatures they will mix completely.
Since oil must pass through the compressor scrolls to provide
lubrication, a small amount of oil is always circulating with the
refrigerant.
Oil circulating in a refrigeration system may be exposed to both very
high and very low temperatures. Because of the critical nature of
lubrication under these conditions and the damage that can be done to
the system by impurities in the oil, use only the proper oil prepared for
the refrigerant and the compressor.
One of the basic characteristics of a refrigerant and oil mixture in a
refrigeration system is the fact that refrigerant is attracted by oil and will
vaporize and migrate through the system to the compressor crankcase
even though no pressure difference exists to cause its movement.
Upon reaching the crankcase, the refrigerant will condense into liquid,
and this migration will continue until the oil is saturated with liquid
refrigerant.
Upon start-up, excess refrigerant in the compressor crankcase may
result in violent foaming and boiling action, driving all of the oil from the
crankcase and causing lubrication problems.
If excessive foaming is noted in the site glass, too much liquid has
returned to the crankcase and the system must be taken out-of-service
until a qualified technician can service the system. Failure to do so can
severely damage the compressor, creating added work and
considerable expense.
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