1
Q
Describe Vapor Cycle Air Conditioning
A
- used on most non-turbine aircraft equipped
with air conditions - not a source of pressurizing air - it only cools
the cabin - it is a closed systems used solely for the
transfer of heat from inside the cabin to
outside of the cabin
2
Q
Define Boiling Point
A
- the temperature at which a substance
changes from a liquid to a vapor - when pressure in liquid increases -the boiling
point increases - when pressure decreases - the boiling point
decreases
3
Q
What temperature does vapor condense into a liquid
A
Boiling Point
4
Q
What are the 2 sides of the Vapor Cycle system?
A
- Low Side - this side accepts heat
- High Side - this side gives up heat
low and high refer to the temperature and
pressure of the refrigerant
5
Q
List the 7 components of the Vapor Cycle Air Conditioning system
A
- Refrigerant
- Receiver Dryer
- Expansion Valve
- Evaporator
- Compressor
- Condenser
- Service Valves
6
Q
Refrigerant - Things to know
A
- R12 - old refrigerant - used in older systems
- R134a replaced R12
- R134a is better for the environment
- R12 and R134a should not be mixed
- gloves, goggles, skin protection required when
using
7
Q
Describe the Receiver Dryer
A
- acts as the reservoir of the vapor cycle system
- located downstream of the condenser and
upstream of the expansion valve - when it is vey hot, more refrigerant is used
8
Q
What is a stand tube used for?
A
- a stand tube is used to remove refrigerant
that may enter the receiver dryer - it runs to the bottom of the unit to ensure all
liquid is withdrawn and sent to the expansion
valve - there is a sight glass at the top allowing tech
to see the refrigerant - bubbles will show if
low on refrigerant
9
Q
What is the Expansion Valve?
A
- refrigerant exists the receiver dryer and flows
to the expansion valve
10
Q
How much refrigerant should the expansion valve release?
A
only the amount of refrigerant spray that can be completely converted to a vapor
11
Q
What determines the amount of refrigerant the expansion valve should spray into the evaporator?
A
the temperature of the cabin air to be cooled
12
Q
What can happen if too much refrigerant is released by the expansion valve into the evaporator?
A
- some of it remains liquid when it exists the
evaporator - it is sucked into the compressor -
could cause the compressor to break
** liquids are not compressible**
13
Q
Describe an Evaporator
A
- made of copper or aluminum tubing coiled
into a compact unit - fins are attached to increase the surface area
- expansion valve located at evaporator inlet
releases high pressure
14
Q
What keeps condensed water from freezing in the Condenser?
A
the continuous movement of warm cabin air around the fins
15
Q
What is the compressor?
A
- the heart of the vapor cycle air conditioning
system - it circulates the refrigerant around the vapor
cycle system - it receives low pressure, low temperature
refrigerant vapor from the outlet of the
evaporator and compresses it. - it is the dividing point between the low side
and the high side of the vapor cycle system - modern compressors are either engine driven
or driven by an electric motor - it is usually a piston type pump
16
Q
What is a Condenser?
A
- the final component in the vapor cycle
- it is a radiator-like heat exchanger situated so
that outside air flows over it and absorbs heat
from the refrigerant received from the
compressor
17
Q
What are Service Valves?
A
- used for servicing of vapor cycle air
conditioning systems - one valve is located in the high side and
one valve is located on the low side of the
system - should always be capped when not in use
18
Q
What is a common type of valve used in a vapor cycle system?
A
- Schrader valve
- operates with R12 refrigerant
19
Q
What 2 other types of valves are used, besides a Schrader valve, in a vapor cycle system?
A
- R134a valve
- fittings are different than Schrader valve
- will not attach to Schrader valve threads
- Compressor Isolation Valve
- serves 2 purposes
- permits servicing of the system with
refrigerant - can isolate the compressor so oil level can
be checked
- permits servicing of the system with
- serves 2 purposes
20
Q
Describe a Compressor Isolation valve
A
- permits servicing of system with refrigerant
- can isolate the compressor so oil level can
be checked
21
Q
What equipment used for servicing Vapor Cycle Systems
A
- Manifold Set, Gauges, Hoses, and Fittings
- Full Service Refrigerant Recovery, Recycling,
Evacuation, and Recharging Units - Refrigerant Source
- Vacuum Pumps
- Leak Detectors
22
Q
Describe the manifold set
A
- contains 3 hose fittings, 2 O-ring sealed
valves, and 2 gauges - it is a manifold into which the gauges, fittings,
and valves are attached - all servicing operations are performed by
manipulating the valves - when not using manifold set - make sure
hoses are capped
23
Q
Describe the gauges on the manifold
A
- the gauges on the manifold are dedicated
- one for the low side of the system and one for
the high side of the system - the low pressure gauge is a compound gauge
- indicates pressure above/below atmospheric
pressure
- indicates pressure above/below atmospheric
Below atmospheric pressure
1. the gauge is scaled in inches of mercury down
to 30 inches - to indicate vacuum
2. 29.92 inches equals an absolute vacuum
(absolute zero air pressure)
Above atmospheric pressure
1. gauge pressure read in psi ranging from 1 - 60
psi ( some go go 150 psi)
2. high pressure gauge - range is 0-500 psi
24
Q
Describe modern refrigeration and recovery units
A
- they perform all of the servicing functions
required for vapor cycle air conditioning
systems - All in one units that have the manifold set
built into the unit - Integral solenoid valves, reservoirs, filters, and
smart controls allow entire servicing
procedure to be controlled from the unit
panel - built-in compressor allows complete system
refrigerant purging - built-in vacuum pump performs system
evacuation
25
Refrigerant - things to know
1. R134a comes in containers measured by
weight of the refrigerant contained
2. 12oz to 2 1/2 lb cans are common for adding
refrigerant
3. 30 and 50lb cylinders with shutoff valves are
used to charge an evacuated system / used in
shops that service vapor cycle systems
26
Describe Vacuum Pumps
1. used with a manifold set or as part of a
service cart
2. connected to the vapor cycle system so the
system pressure can be reduced to a near
total vacuum - this removes all water from the
system
27
What can happen if water is left in the vapor cycle system?
1. water can freeze causing the system to
malfunction
2. water can combine with the refrigerant to
create corrosive compounds
28
Describe the types leak detection in vapor cycle systems
1. Electronic leak detectors
2. soapy solution applied to fittings
3. special leak detection dyes can be injected
4. visual inspections
29
What 8 tests/steps are performed when servicing a Vapor Cycle Air Conditioning System?
1. Visual inspection
2. Leak Test
3. Performance Test
4. Feet Test
5. Purging the System
6. Checking Compressor Oil
7. Evacuating the System
8. Charging the System
30
During the visual inspection - what should you pay special attention to?
1. Evaporator Fins - should be checked - clean,
unobstructed, and not folded from impact
2. Condenser - check for debris that may restrict
airflow / make sure fan operating correctly
3. Hinged Units - check for security and wear
4. Capillary Temperature Feedback Sensor -
make sure securely attached to evaporator
outlet
5. Evaporator - check for ice
6. Fan Blower - make sure rotates freely
31
What are the signs/indications that there is a leak in Vapor Cycle Air Conditioning system?
1. low refrigerant
2. bubbles in sigh glass
32
How do you locate the leak point in a Vapor Cycle Air Conditioning system?
1. partially charge system with refrigerant -
about 50 psi in the high and low sides
2. by introducing refrigerant into the high side,
pressure indicated on the low side gauge
verified the orifice in the expansion valve is
not clogged
33
When all refrigerant is lost in a Vapor Cycle system - what should be done?
A full system evacuation must be performed after the leak is found and repaired
34
What happens when a Vapor Cycle air conditioning system loses all of its refrigerant charge?
1. air and water can enter the system
2. a full system evacuation is required after the
leak is found and repaired
35
Performance Test of the Vapor Cycle air conditioning system - things to know
1. involves operating the system and checking
parameters to ensure they are in normal
range
2. A key indication of performance is the
temperature of the air that is cooled by the
evaporator - this can be measured at the air
outflow from the evaporator - thermometer
should read 40-50 degrees
3. Pressures can also be observed
a. low side pressure is normally 10-50psi
b. high side pressure is 125-250psi
4. all system tests are performed at a specified
engine rpm
36
Feel Test on a Vapor Cycle air conditioning system - things to know
1. components and lines in the high side (from
compressor to expansion valve) should be
warm or hot to the touch - lines on both sides
of the receiver dryer should be the same temp
2. Low side lines and the evaporator should be
cool - no ice should be visible
37
Purging the Vapor Cycle air conditioning system
- what does it mean
- things to know
Meaning: Purging the system means emptying of
its refrigerant charge
1. A service cart is required since the refrigerant
must be captured
2. vapor cycle systems must be properly purged
before opening for maintenance or
component replacement
38
Describe the process for purging a vapor cycle air conditioning system
1. Connect hoses to the high side and low side
service valves
2. Select recover, cart solenoid valves position so
that a system pursing compressor pumps the
refrigerant out of the vapor cycle system and
into a recovery tank
39
Evacuating a vapor cycle air conditioning system
- what does this mean
- when is this done
Meaning: water is removed from the system - also known as pumping down the system
When done:
1. anytime the system refrigerant charge falls
below atmospheric pressure
2. the refrigerant charge is lost
3. the system is opened
40
What 2 types of oxygen systems are used on civilian aircraft?
1. Gaseous
2. Solid oxygen (oxygen generators)
**Can be built-in o portable oxygen systems**
41
Gaseous Oxygen Systems - things to know
TYPES:
1. can be a small carry-on portable cylinder w/ a
single mask (found on light aircraft)
2. can be a larger carry-one portable cylinder
fitted with a regulator that divides flow to 2-4
people (found on light aircraft)
3. can be be a built in system with a distribution
system to multiple breathing stations (high
performance and light twin engine aircraft)
4. Transport aircraft may use elaborate built in
gaseous system as a backup system to cabin
pressurization
42
How is oxygen stored on aircraft for gaseous oxygen systems?
1. oxygen is stored as a gas at atmospheric
temperature in high pressure cylinders
43
Describe Oxygen Storage Cylinders
1. traditionally heavy steel tanks rated for 1800-
1850 psi & capable of maintaining pressure up
to 2400 psi
2. some newer cylinders made of lightweight
aluminum shell wrapped with Kevlar are being
used - can carry same amount of pressure as
steel tanks, but much lighter
3. Heavy walled all aluminum cylinders are
commonly used for portable carry on tanks
4. certified to DOT specifications
5. must be hydrostatically tested periodically
6. cylinders must be removed from service after
a specified number of filling cycles or calendar
age
7. most commonly used heavy duty steel
cylinders used are 3AA and3HT
8. oxygen cylinders are considered empty when
the pressure inside drops below 50 psi
44
When should oxygen cylinders be removed/replaced?
cylinders must be removed from service after
a specified number of filling cycles or calendar
age
45
What are the most commonly used heavy duty steel oxygen cylinders?
3AA and 3HT
46
When are oxygen cylinders considered empty?
oxygen cylinders are considered empty when
the pressure inside drops below 50 psi
47
The design of various oxygen systems used in aircraft depends on what?
1. its operational requirements
2. whether the aircraft has a pressurization
system
48
How are oxygen systems characterized?
By the type of regulator used to dispense the oxygen
1. continuous flow system
2. demand flow system
49
Describe the continuous flow sytem
1. Once the valve is opened, the flow of oxygen
is continuous until the valve is closed
2. A portable oxygen setup for a light aircraft is
an example of a continuous flow system
3. Some more advanced systems use a regulator
that is adjustable - provides varying amounts
of oxygen based on altitude increases
4. The regulators can be manual or automatic
5. many systems include a fixed location for the
oxygen cylinders w/ permanent delivery
plumbing installed to all crew and passenger
stations
50
How are manual continuous flow regulators adjusted
They are adjusted by the crew as altitude changes
51
Describe automatic continuous flow regulators
How do they work?
1. have a built in aneroid
2. as the aneroid expands with altitude, a
mechanism allows more oxygen to flow
through the regulator to the users
52
Describe fully integrated oxygen systems and how they work
1. usually have separate, remotely mounted
components to reduce pressure and regulate
flow
2. A pressure relief valve, a filter, and a gauge to
indicate amount of oxygen pressure remains
in the cylinder
53
Describe a built-in continuous flow gaseous oxygen system and how it works
1. accomplishes a final flow rate to individual
user stations through the use of a calibrated
orifice in each mask
2. Larger diameter orifices are usually used in
crew masks to provide greater flow than to
passengers
54
What is a demand flow oxygen system?
1. oxygen is delivered only as the user inhales
2. used most frequently by the crew of high
performance and air transport category
aircraft
3. Similar to continuous flow systems, except the
demand flow oxygen regulators differ
significantly
55
Describe how a demand-flow oxygen system works
1. The pressure reducing valve (pressure
regulator) lowers the oxygen pressure from
the storage cylinder(s) to 60-85 psi and
delivers to individual regulators
2. A pressure reduction also occurs at the inlet
of the individual regulator
56
What are the two types of individual regulators
1. diluter-demand type
2. pressure-demand type
57
Airframe Test
flashcards
Decks in class (11)
# Cards
-
Layout, Forming, and Drilling of Sheet Metal Components77
-
Selection of Rivets, Hardware, and Fasteners for a Sheet Metal Repair11
-
Wood structures25
-
Thermoplastic material inspection/types of defects24
-
Flight Controls58
-
Airframe Inspection7
-
Landing Gear Systems101
-
Environmental Systems57
-
Electrical System100
-
Aircraft Lighting5
-
Aircraft Batteries4
