Twist TwistAero PCA090480WH User manual

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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
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CHAPTER 2
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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
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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.
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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.
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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.
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Section 2: Safety Precautions
2-2 March 2013
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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.
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Section 3: Refrigeration Basics and Service
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© 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.
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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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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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3. Servicing System and Charging
A. Gauge Manifold
The most important tool of the refrigeration serviceman is the gauge
manifold. It can be used for checking system pressures, charging
refrigerant, evacuating the system, purging non-condensable and
adding oil.
The gauge manifold consists of compound and high pressure gauges
mounted on a manifold with hand valves to isolate the common
connection or open it to either side as desired.
The left-hand gauge is a compound or suction pressure gauge. The
right- hand gauge is the high or discharge pressure gauge. Flexible
hoses are used to make connections from the manifold to the system.
Connecting the gauge manifold to a system is the most common service
function. To avoid introducing contaminants into the system, always
purge the hose connections with refrigerant. The service person
making the connections should always follow a consistent procedure.
Crack (open slightly) the high-pressure manifold valve, allowing
refrigerant to bleed through the common hose. Allow refrigerant to
bleed for a few seconds then close the high-pressure valve on the
manifold. Repeat the same procedure with the low-pressure valve.
Close the valves on the manifold and crack the low-pressure service
valve, connecting the manifold to the system, making it ready for use.
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B. Service Valves
Schrader type valves are used on the PCA unit.
The Schrader type valve is for convenient checking of system pressures
or charging refrigerant without disturbing the unit’s operation. An
adapter is necessary for the standard service gauge or hose connection
to fit the Schrader type valve.
The valves are located on the compressor piping leading to each
compressor. Once connections are made, ensure that all service doors
are closed as much as possible to allow proper airflow through the
condenser coils.
C. Removing Refrigerant
Occasionally it will be necessary to remove the refrigerant from a
system. This may be required in order to repair leaks or make other
repairs. If a system has been overcharged, it may be necessary to
remove the excess charge to insure proper system operation.
EPA Regulations prohibit venting refrigerant into the atmosphere.
Always use a refrigerant recovery system. Check the instructions on
the recovery system for proper operation and follow the latest EPA
Regulations for refrigerant disposal and records. Check the oil level in
the compressor crankcase after the refrigerant is removed.
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D. Adding or Removing Oil
Visually check the oil level in the compressor. The oil level should be
visible in or slightly above the center of the sight glass but not below it.
Keep in mind that some slight fluctuation in oil level may occur during an
operating cycle. As long as the oil level is maintained well within the
sight glass, such fluctuations are not harmful. On two compressor sets,
one compressor oil level could be below the sight glass when it is first
started but should come back after five minutes.
NOTE: If the oil is black in color, call a qualified service technician
because the oil is contaminated and should be replaced.
Unless there are particular reasons for changing the oil, do not
change it. The oil does not deteriorate or wear out with normal
usage.
Excess oil can be removed from the compressors’ crankcase at the Oil
Charging Valve, which is located beneath the oil level of the
compressor. To remove oil, connect a manifold hose to the Oil
Charging Valve connection, open the manifold valve slowly, and allow
the oil to run into a suitable container. Take special care when
removing the oil because of oil foaming. The foaming not only may
cause the oil to overflow from the container into which it is being drained
but also make it difficult to determine the amount of oil being removed.
When sufficient oil has been drained, close the manifold valve tightly
and start the compressor. Allow the compressor to run for
approximately one-half hour and then recheck the oil level.
For adding oil:
(1) Insert an oil pump into the oil container until it touches the bottom
and push the universal stopper down into the neck opening of the
container. (A little oil will keep the stopper from sticking.) The
function of the stopper is to stabilize the pump and keep out
contamination.
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(2) Connect either copper tube or a manifold charging hose to the
1/4" flare fitting at the top of the pump and attach the other end
loosely to the valve on the compressor. Next, purge the air from
the hose and tighten the fitting at the system.
(3) When it has been connected and purged, start pumping the oil
into the compressor with slow, even strokes. Always push
straight down on the pump.
(4) After pumping the desired charge of oil into the compressor,
remove the connecting hose or tube from the system. Cap the
flare connection on the pump to help keep it clean and free of
contamination.
E. Dealing with Non-Condensable Gases
A leak in the low-pressure side of an operating system may result in the
entrance of air. Before purging non-condensable gases from a system,
note the compressor operating discharge pressure and compare it with
the temperature of the refrigerant (see Appendix). Since air is non-
condensable under the temperatures and pressures encountered in an
air conditioning system, the system’s condensing pressure will increase
due to the pressures exerted by the trapped air. The amount of
increased pressure is dependent on the quantity of air trapped.
If non-condensable gases are suspected in the system, remove the
refrigerant charge and evacuate the system to get rid of the non-
condensable gases. Once this is completed, recharge the system with
the correct amount of refrigerant.
F. Refrigerant Leaks
Refrigeration systems must be absolutely air tight for two reasons:
First, any leakage will result in loss of the refrigerant charge. Second,
leaks allow air and moisture to enter the system, causing damage to
components.
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Leaks can occur not only from joints or fittings, but also from line
breakage due to vibration, gasket failure, or other operating
malfunctions.
The common means of pressure testing a system for leaks include the
following:
(1) If the system is not already charged with refrigerant, it is more
economical and just as effective to slightly charge with refrigerant
and then use an inert gas such as dry nitrogen or dry carbon
dioxide to build up pressure in the system to approximately 175
psig for testing purposes.
WARNING: NEVER USE OXYGEN FOR PRESSURIZING A
SYSTEM; AN EXPLOSION MAY OCCUR IF OIL IS
PRESENT IN THE SYSTEM. ALWAYS USE A GAUGE
EQUIPPED PRESSURE REGULATOR ON THE HIGH
PRESSURE BACK-UP GAS, AND NEVER
INTERCONNECT THE REFRIGERANT CYLINDER AND
THE INERT GAS CYLINDER THROUGH A GAUGE
MANIFOLD. NITROGEN AND CARBON DIOXIDE
CYLINDER PRESSURES CAN RUPTURE A
REFRIGERANT CYLINDER.
The electronic leak detector is the most sensitive type available
and can detect small leaks of a fraction of an ounce per year,
often missed when using other testing methods. Because of their
extreme sensitivity, only use electronic detectors in a clean
atmosphere not contaminated by refrigerant vapor, smoke, vapor
from carbon tetrachloride, or other solvents, which may give a
false reaction.
(2) Yet another method is by means of soap bubbles. Swab a
suspected leak with liquid soap or detergent, and bubbles will
appear if a leak exists. Despite its simplicity, the soap bubble
method can be extremely helpful in pinpointing a leak that is
difficult to locate.
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When a leak is located, mark it. When leak testing is completed and all
leaks have been located and marked, vent the test pressure gas. If a
leak requiring brazing is found in the high-pressure side of a system
containing a refrigerant charge in a location that cannot be isolated,
remove the refrigerant in order to make repairs.
When pressure has been removed from the area where the leak is
located, repair the leak. It may be necessary to re-braze fittings,
replace gaskets, repair flare connections, or merely tighten connections.
When all leaks have been repaired, pressurize the system again and
repeat the leak testing process.
Pressure leak testing is necessary to locate individual leaks. In order to
determine if the system is free of all leaks, a vacuum test is helpful.
After repairing all known leaks, draw a deep vacuum on the system with
a good vacuum pump. Reduce the pressure to 1 psia or less (the
vacuum registered on the test gauge will vary with atmospheric
pressure), reseal the system, and leave it for at least 12 hours. Any
leakage of air into the system will cause the vacuum reading to
decrease. (Changes in ambient temperature may cause some slight
change in pressure.) If an air leak is indicated, again pressure leak test
the system and locate and repair the leaks.
G. Brazing Refrigerant Lines
The refrigeration system must be leak free. Clean and burnish the
tubing bright before brazing. Care in cleaning is essential for good gas-
tight connections. Give particular attention to preventing metal particles
or abrasive material from entering the tubing.
A suitable low temperature brazing flux that is fully liquid and active
below the flow point of the brazing alloy is required. Brazing fluxes are
quite active chemically and must be kept out of the system. Only flux
the male connection and use only enough flux to adequately cover the
surface.
When heat is applied to copper in the presence of air, copper oxide is
formed. This oxide can be extremely harmful to a refrigerating system.
To prevent its formation, sweep an inert gas such as dry nitrogen
through the line at low pressure during the brazing operation. Always
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use a pressure-regulating valve in the line connecting the nitrogen
cylinder to the system.
Apply heat evenly to the tube and fitting until the flux begins to melt.
The way heat is applied can either draw flux into the joint or prevent its
entry. Apply heat around the circumference of the fitting to draw the
brazing alloy into the joint, making a mechanically strong and tight joint.
Never apply heat to a line under refrigerant pressure. The line may
rupture, and the escaping refrigerant pressure may throw blazing oil or
molten solder through the air. Refrigerants exposed to an open flame
may break down into irritating or poisonous gases.
Immediately after the brazing alloy has set, apply a wet brush or cloth to
the joint to wash off the flux. All flux must be removed for inspection
and pressure testing.
H. Pressure Testing
After repairs are made on a system, refer to sub-section “F” above to
review pressure-testing options. Ensure that no leaks exist before
proceeding forward. If leaks are noted, remove pressure from system
and re-solder joint(s) per sub-section “G.”
I. Evacuation
Any time the compressor or system is exposed to atmospheric air or if
the system becomes contaminated and removal of the refrigerant
charge is necessary, evacuate the system. Use a portable vacuum
pump specifically built for refrigeration evacuation purposes. The gauge
manifold provides a convenient means of connecting the vacuum pump
to service valves on the compressor.
Triple evacuation is strongly recommended if possible. To evacuate a
system, attach the common connection on the gauge manifold to the
suction connection on the vacuum pump. Connect the “High” and “Low”
pressure connections on the gauge manifold securely to the service
valves on the “High” and “Low” pressure sides of the system
respectively and close the valves on the gauge manifold.
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Start the vacuum pump and gradually open the gauge manifold valves.
It may be necessary to restrict the vacuum pump suction pressure by
means of the gauge manifold valves to avoid overloading the pump
motor. Continue evacuation until the desired vacuum reading on “Low
Pressure” gauge is reached.
When evacuation is complete, close the gauge manifold valves tightly,
remove the line from the vacuum pump, and connect it to the refrigerant
cylinder. Loosen the common hose connection at the gauge manifold,
crack the refrigerant drum valve to purge the hose, and retighten the
hose connection. Crack the valves on the gauge manifold until the
system pressure rises to 2 psig. Close the refrigerant drum valve and
the gauge manifold valves.
For triple evacuation, repeat the above procedure three times,
evacuating twice to 1500 microns and the last time to 500 microns.
When the procedure is complete, the system is ready for charging.
J. Charging
With the gauge manifold connected to the service valves of the system,
connect the common hose to the refrigeration cylinder. Loosen the
common hose connection at the gauge manifold, crack the refrigerant
drum valve to purge the hose, and retighten the hose connection.
Weigh the refrigerant cylinder prior to charging. Open the refrigerant
cylinder vapor valve, open the suction valve allowing pressure to build
up in the system, and start the compressor. Modulate the rate of
charging with the gauge manifold valve.
The refrigerant cylinder must remain upright with refrigerant withdrawn
only through the vapor valve to insure that only vapor reaches the
compressor. The vaporizing of the liquid refrigerant in the cylinder will
chill the liquid remaining and reduce the cylinder’s pressure. To
maintain cylinder pressure and expedite charging, warm the cylinder by
placing it in warm water or by using a heat lamp. Do not apply heat
with a torch.
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To determine if sufficient charge has been introduced, close the
refrigerant cylinder valve and observe the system operation. Continue
charging until the proper charge has been added. Again weigh the
refrigerant drum and subtract the previously determined weight to
ensure that only the proper amount of refrigerant has been added.
At times the sight glass may show bubbles or flash gas even when the
system is fully charged. A restriction in the liquid line ahead of the sight
glass may cause a sufficient pressure drop to cause flashing of the
refrigerant. If the expansion valve feed is erratic or surging, the
increased flow when the expansion valve is wide open can create a
sufficient pressure drop to create flashing at the receiver outlet. Rapid
fluctuations in condensing pressure can also be a source of flashing.
While the sight glass is a valuable aid in determining the proper charge,
the system performance must be carefully analyzed before placing full
reliance on it as a positive indicator of the system charge.
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Section 4: Introduction to Preventive Maintenance Checklists
March 2013 2-4
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1. Introduction
The following checklists cover all points to be inspected and/or adjusted. A
space is provided for the maintenance person to initial. Twist, Inc. suggests
those responsible for unit upkeep make copies of these checklists, give them
to the maintenance personnel, and after the service work is completed, bind
these checklists into a history of the work performed. The maintenance
history must be accessible for review when filing warranty claims.
The checklists are numbered as follows:
(1) Quarterly
(2) Semi- Annual
(3) Seasonal
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