HET 4 A/C Flashcards
190403 A,B,C
Most people feel comfortable at what temperature?
70-75°F (21-25°C)
What is the ideal cab humidity level?
40-45%
AC adds or removes humidity?
Removes humidity
Heat energy moves from hot to cold or cold to hot?
Hot to cold
Heat moves in three methods, what are they?
Conduction, Convection, Radiation
Where are condensers usually located?
Front or Roof of cab
Conduction transfers heat in what way?
Heat energy from one particle to another particle
How is heat transferred through convection?
by movement of warm gases or liquids
Radiation can be described as?
Electromagnetic rays or moving particles moves the heat
Sun heat coming through the window of a cab is what type of heat movement?
Radiation
Heat is measured in two ways, what are they?
Heat Intensity
and
Heat Quantity
A well running A/C unit will drop the temperature by what?
30°F drop from ambient temp
At what temperature does water freeze at?
0°C or 32°F
What is the boiling temperature of water?
100°C or 212°F
When liquid changes into a solid, it is called?
Fusion Freezing
Melting is what types of state changes?
Solid changes into a liquid
A liquid has turned into a vapour what has occurred?
Evaporation or Vaporization
What can be superheated?
Vaporized refrigerant
What does superheat protect compressor from?
Liquid refrigerant
What condition is the refrigerant in when it is considered subcooling?
Refrigerant is completely liquid
At what temp does R134A boil at?
R134A boils at -26°C
How is subcooling degrees found?
High side pressure gauge reading (convert to temp) then subtract condenser outlet temp from that.
Why was R-134a preferred over R-12?
R-12 destroyed the ozone - R-134a is environment friendly
Refrigerants are usually what colour?
No colour
What colour are the containers that have R-134a in it?
Light blue (Sky Blue)
What colour are the containers for R-12?
White
What colour is the container that has R-22 refrigerants in it?
Light Green colour
What temperatures can the AC system get to in the summer?
350 PSI
Why should refrigerant not be released to atmosphere?
To protect the environment and is economical
What are the three types of refrigerant lubricant?
Mineral oil MO
Polyol Ester POE
Polyalkylene Glycol PAG
Mineral oil is used with what type of refrigerant?
R-12
POE and PAG lubricants are used in what systems?
R-134a
If MO and PAG lubricants are mixed together what will most likely happen?
lack of lube faults
What can POE lubricants be mixed with?
Mineral oil and PAG
What are the components of an AC system?
Condenser Compressor Expansion Valve Evaporator Receiver/Dryer
Where is an evaporator usually located?
In Cab - to pull heat out
A condenser’s basic purpose is?
To give heat to atmosphere
What are the four events the refrigerant undergoes?
Expansion
Evaporation
Compression
Condensation
What type of material make up an AC coil?
Copper or aluminium
Is the Condenser in the high or low pressure side of the AC system?
High pressure side
Is the Compressor part of the high or low pressure side of an AC system?
Half is high pressure
Half is low pressure
Is the refrigerant liquid or vapour in the condenser?
Half liquid
Half Vapour
As pressure goes up what does temperature do?
go UP
Low pressure will have what temperatures?
Lower temps
On the high pressure side of the compressor the line will have what in it? (cold, hot, vapour, liquid)
Hot Vapour
As ambient temperature goes up what will happen to the temperatures in the AC system?
Go up (all sides of the system)
If a compressor gets fluid in it, what would it sound like?
Cavitation, will cause damage
Tin plate (reed valve) on a compressor valve plate would indicate inlet or outlet side?
Inlet side
Does belt tension matter on the compressor?
Yes
What type of clutch does the ac compressor use?
stationary electromagnetic
The clutch hub is splined to what component on the compressor?
The compressor drive shaft (front of compressor)
What types of access valves are used on the AC systems?
Schrader or stem type
For the AC system to work normally what position does the stem type service valve need to be in?
Backseat (open)
To isolate a compressor what position does the AC stem type service valve need to be in?
Frontseat - closed
What size are the threads on a schrader valve on a AC system?
1/4 inch SAE is most common
can see 3/16 SAE flare or metric
What is a common fault for loosing refrigerant?
Leaking schrader valve
Are the R-134a quick disconnect fittings the same as all other systems?
No, low pressure as a small valve
high pressure has a larger valve
no external threads
Schrader type
What are the classes of condensers?
Tube and fin
serpentine
parallel flow
What is the most expensive type of condenser?
Tube and Fin
What is the most common type of condenser?
Parallel Flow
What is the largest most inexpensive condenser?
Parallel Flow
What material is in the receiver/dryer?
Filters/Screens and Desiccant
Where is the receiver/dryer mounted in the ac system?
Between the condenser and expansion valve
What is important for a technician to know about the desiccant in the receiver/dryer?
If it is compatible with the refrigerant used
What are the three functions of a receiver/dryer?
Storage of refrigerant
Dryer
Filter
What label is on the receiver/dryer that shows its compatible with R-134a?
XH-7 or XH-9
What is installed on the receiver/dryer or moisture indicator, incase of a fire?
Fusible Plug
At 240°F, what will happen to the AC system?
The fusible plug will open and vent refrigerant to atmosphere
An internally equalized thermal expansion valve has how many capillary tubes?
one
Some thermal expansion valves may need what wrapped around them?
Insulating material
On thermal expansion valves that are externally equalized, do they always have one temp sensing bulb?
They can have multiple up to 17
True or False?
An orifice tube has moving parts and changes how much refrigerant is sent through the system?
False
How do the colours of an expansion tube help a technician?
Colour shows what refrigerant and how much it allows through
What is the normal temperature range for superheat?
8-12°F
What is the normal temperature range for subcooling?
12-21°F
A compressor with a green wire is what voltage system?
24V
A compressor with one black wire needs how many volts to work and grounds to?
12V - source to actuate
grounds through body to frame
At what degree does water freeze?
0°C or 32°F
If a condenser starts to become plugged what will be the complaint?
No AC in stop/go traffic but works fine at highway speeds
On a hot day the technician finds high super heat, and low gauge reading, what could be the fault?
TXV may be freezing due to moisture in system
A piece of equipment runs in a climate that is usually below 7°F, the technician finds the TXV freezes up regularly. What could be the cause of the fault?
Plugs are missing from schrader valves
Ambient temp/air is opening the schrader and moving air/moisture into the AC system
What are the three types of HVAC controls?
Active controls
Passive (automatic) controls
Combination and supplemental control devices
What type of control is used by the operator?
Active controls
Where are active controls mounted?
Dash mounted
HVAC air velocity is measured in?
Cubic Feet Per Minute CFM
Ambient Temperature switches, Multi-function pressure switches, radiator fan clutches and radiator shutter systems are all examples of what type of HVAC control?
Combination and supplemental controls
How can flow be divided to two areas at the same time?
in bi-level position
If the gas charge is lost, what is the operators complaint? AND what will the technician notice?
AC does not work
Compressor will NEVER run
Where is the sensing bulb in the evaporator?
Lower 3rd (coldest) Evap Outlet
What causes the temperature drop in a fixed orifice tube?
Pressure difference, pressure drop
What could moisture in the system do to an AC system?
Cause rust and freezing
What is inside an air condition hose that keeps the tiny molecules from escaping?
Elastomeric layer - internal barrier liner
A detached sensing bulb could cause what fault in the system?
Slug the compressor
If a sensing bulb is sensing ambient temperature when will the operator complain?
On hot days
Engine coolant water valves are located where?
Upstream from heater core
Why would a flow restricter be used in a water valve?
To slow the coolant so heat has time to transfer into cab
What type of lubricant should be used to install fittings onto AC hose?
Mineral oil - does not attract moisture
Is refrigerant heavier than air?
Yes
Where should hoses be checked for leak?
On the lower side of hose/fitting
at the hole in the fitting
What can prevent coolant hot spots?
H fitting in series with heater core
What could cause a bad crimp of an AC hose fitting?
Worn out crimping tool
Crimping tool not square in press
Wrong/damaged fitting
CCOT stands for?
Clutch cycling switch
Where is hidden heat?
In the evaporator, when the state of change happens to the refrigerant but not CHANGE in temperature
What state does the refrigerant have to be in to pass through the compressor and not cause damaged?
Vapour
How is the temperature controlled in the evaporator in a fixed orifice tube system?
Cycling the compressor clutch on/off
Trinary switch has three functions what are they?
Protects against low pressure/temp
Protects against high pressure/temp
Controls shutters
How many prongs/connections do trinary switches have?
4 prongs
What is used in a bunk model to control the AC system in the sleeper?
Electrically controlled refrigerant solenoid valve
Due to truck idling laws what is used to keep the sleeper temperature comfortable?
Fuel fired air heater
or
Auxiliary power units
What is used to warm the engine and give problem-free engine starting?
Fuel fired coolant heater
How much oxygen do we need in our air to survive?
9%
How much can you fill an AC container?
80% MAX
What is used to test/pressurized an AC system to check for leaks?
Nitrogen only
Who approves refrigerant recovery containers?
CTC
What can a refrigerant identifier diagnose?
Purity of refrigerants, propane and butane
and air %
When refrigerant is released into atmosphere, how fast does its temperature drop?
Instantly
How long is the condenser fan on when driving less than 8km/h?
180 seconds
What is considered low voltage in a 12V system?
11V or less
What is considered high voltage in a 12V system?
Above 16V
What is the normal AC compressor delay during engine cranking?
15 seconds
What are the three types of refrigerant flow control?
H-block style thermal expansion valve
Thermal expansion Valves
Fixed orifice expansion tubes
What are the normal speeds on an HVAC blow motor?
1-4 speeds
How many shafts are there on an HVAC blow motor?
single or double shaft
How many evaporators are on a truck with a sleeper?
2 evaporators
What is needed to split refrigerant flow on a truck with a sleeper?
Refrigerant solenoid valve
Where is the Trinary switch located on the AC system?
Between condenser and expansion device
What three ranges does the trinary switch monitor?
High pressure
Low Pressure
MID range pressure - fan/shutter control
At what temperature should the CCOT disengage the compressor clutch?
32°F
If the refrigerant pressure is 24 PSI, what temperature is in the evaporator?
32°F
What are the 3 information sources when diagnosing HVAC faults?
Tech’s own experience and knowledge
Operator
HVAC Testing
What are the three abnormal conditions in the AC system?
- Lower than normal low and high side pressures with warm duct air
- Higher than normal low side pressure and lower than normal high side pressure and warm duct air
- Higher than normal low side and high side pressures and warmer than normal air ducts
The gauges show lower than normal on the low and high side. The duct air is still cool. Why?
Operating at low ambient temp (below 65°F)
If refrigerant has been over charged what fault could happen to the compressor?
Damage Reed Valves - Slugging compressor
Cold weather operation can cause what problems with the AC compressor?
Slugging
If the H-block expansion valve is stuck open, what faults will occur?
Slugging compressor
No Super Heat
No meter of refrigerant
After 30 minutes of running the vacuum pump how much PSI or In Hg should their be on the compound gauge?
15 in Hg
A compressor is cycling on and off quickly, what could be the fault?
Undercharged system
AC drive belt should have how much movement in the belt (full spread)?
1/2” per foot
1/4” up and 1/4” down
What are the 6 possible air flows?
MAX NORM BI-LEVEL VENT HEATER DEFROST
Describe the HVAC system when MAX COOL is selected?
Re circulation cab air No coolant to heater core Temp to cold Floor/Panel air defrost is closed max blower motor
In max defrost setting is the ac clutch engaged or disengaged?
Engaged, AC compressor is running
What are the four steps that make up the recovery process?
Recover
Reuse
Recycle
Reclaim
True or False
A charge of 200 PSI of Nitrogen is safe.
True
True or False
Small AC components should be flushed?
False - should be replaced
Evaporators are worth flushing?
Yes
At what temperature does a refrigerant container need to be for 10 hours to find out how much air is present?
65°F (19°C)
What should AC components be flushed to remove contaminates during a rebuild?
Refrigerant oils or Approve flushing agent (many are illegal)
According to CTC, If temperatures stay below 50°C how full can a refrigerant container be filled?
80%
According to CTC, a container can only be filled to 60% in conditions where the temperature is over 50°C.
True or Fase
True
Which Protocol that was signed in Canada that protects the environment?
Montreal Protocol
What are the three types of UV rays that the Ozone layer protects the earth from?
UVB, UVA, UVC
How many GWP units does R-134a have?
1200 units
How far is the ozone layer from the earth’s surface?
15-40KM above
When should a technician pry on a compressor?
NEVER
What is the max tension an AC belt should be ?
110lbs of tension
How often should a visual inspection be done on a HVAC system?
6 months
Why should you remove a AC compressor belt during a 6 months inspection?
Checking bearings
Check the seal
Check the pulley condition
How can frozen coolant affect a heater core?
Can be deformed or split
What could cause an engine to over heat when the AC is on?
Wrong/Failed Thermostat
What heating system tools are used?
Pressure Testing
Hydrometer
Thermostat test
Why would a technician comb a evaporator?
To break up debris and straighten fins before cleaning with low pressure air/water
What pressure should nitrogen be when forcing oil compressor oil in?
50PSI
After a bubble is made what should be done to confirm it is accurate?
Measure the crimp in 3 spots with a micrometer
How far should the crimp start on the fitting sleeve?
1/4” or 7mm from the sleeve opening
What conditions will shut off the AC?
Low static refrigerant pressure
Open or Short in air conditioning electromagnetic clutch circuit
If a technician opens high and low gauges at the same time on a running engine what could happen?
Slug compressor
How long should a vacuum of 500 microns be held for by the vacuum pump?
20 minutes
What is the purpose of the scale for the refrigerant container?
Accurate measurement of refrigerant
What are the two ranges available on a compound gauge?
0-150 PSI
0-30 in Hg
What can be done with a manifold gauge set?
Safe access to system for diagnosis and checks
Remove Air/Moisture
Recover or Add refrigerant
What should be the duct temperature of a CCOT system?
46°F
In a CCOT system, the technician finds the inlet to the accumulator is warm. What is the fault?
Undercharged system
When retrofitting a R-12 system to a R-134a system, how much should the system be recharged to? (%)
80%
What can be used to test pressure switches to make sure they are working correctly?
Nitrogen
Without a manufacture specification around how much oil can be put into a compressor? (max oz)
8oz
A R-134a system needs how many cubic inches of desicant?
15 Cubic inches
When pulling a vacuum (evacuating) an AC system, how many microns should be held in vacuum for 5 minutes to prove the system is leak free?
500 microns for 5 minutes
What is the fastest way to recharge an AC system? Vapour or Liquid
Liquid
True or False
Oil can be added to a system during evacuation?
True
HRAI stands for?
Heating, Refrigerating and Air Conditioning Institute of Canada
