Split Systems Flashcards
Which gauge on the manifold gauge is considered to be the compound gauge?
The low side gauge (blue) is a compound gauge
Name four main types of electronic leak detectors?
Ion source detection, thermistor type, halogen type, and ultrasonic type
What is the difference between a recovery unit and a recycle unit?
Recycle units work in the same manner as the recovery units, but they take it one step further by adding filters and oil separators that remove any compressor oil, moisture, and some contaminants from the refrigerant
What is the maximum capacity of any service or storage cylinder used for refrigerant?
Must not be filled 80 percent of its capacity
What does reclaiming the a refrigerant mean?
It is cleaned and processed to new specifications
Why should nitrogen be purged through the copper lines when they are being brazed?
To prevent oxidation
How should we purge nitrogen through the copper lines when they are being brazed?
By allowing a small amount of nitrogen into the system at a very low pressure less than 2 psig.
Which hoses are connected to each service valve?
The low pressure gauge (blue gauge) goes to the low pressure side of the system. The high pressure side (red gauge) goes to the high pressure side of the system. The centre hose in connected to the inlet port on the recovery unit.
What color is the gauge on the low pressure gauge?
Blue
What color is the gauge on the high pressure gauge?
Red
To what pressure should the system be tested when dealing with refrigeration?
A pressure between 125 psi to 150 psi is considered safe for most systems.
Removing the stem in the Schraeder valve speeds up the evacuation process. True or False?
True
What amount of vacuum must be obtained to render the system free of refrigerant?
10” to 11” of Hg
What are the two reasons for performing a deep evacuation?
To remove moisture, and to remove non-condensable gases
When is a triple evacuation used?
If the system is deemed to be dirty or wet
How many CFM is required for each ton of cooling?
Between 400 CFM to 425 CFM per ton of cooling
What are the two methods of calculating the CFM in a system?
Calculating by temperature rise across the evaporator coil and calculating by static pressure across the evaporator coil.
Which ways of calculating CFM is one of the most accurate?
The static pressure method
Which method is used for checking the refrigeration charge on a system equipped with a TXV?
The method of checking for proper sub-cooling
We as sheet metal workers are allowed to service and install cooling systems up to and including?
60 000 Btuh (5 tons)
What are installed on all newer condensing units?
Both liquid line and suction line service valves are installed on newer units.
What is a manifold gauge set used for?
To diagnose and service air-conditioning and refrigeration systems properly.
What color is the centre hose manifold gauge usually?
Yellow
What are the yellow hand valves on the manifold used for?
To perform recovery, evacuation and recharging procedures.
What is the sight glass on the manifold used for?
It allows you to see if there is a liquid, gas bubbles, or vapour in the system.
What should you always do when using gauge sets that were used on different refrigerants in order to avoid cross contamination?
Purge the lines with nitrogen
Most copper tubing has a max pressure of?
700 PSI
What are three styles of gauges used in the refrigeration field?
High pressure, vacuum, and compound gauges
Always remember gauges should never be subjected to more than ____ of their full scale range on the gauge face.
75 percent
Hoses are constructed to withstand pressures in excess of?
500 psi (burst pressure 2000 psi)
Which color on the hoses is used for charging and evacuating?
Yellow or black
All hoses must have?
Shut off devices to prevent the introduction of air into the system.
When servicing air conditioning systems, what are the three ways of identifying the refrigerant?
Labels, service fittings, and using a refrigerant identifier
Many refrigerants are ___ and ___.
Colourless and odourless
What is the only way to test refrigerants?
By using a refrigerant identifier
How do ion source leak detectors detect leaks?
By using the positively charged particles in the refrigerant
What do halogen leak detectors only work on?
Halogen based refrigerants such as R-12 and R-22
How do ultrasonic leak detectors detect leaks?
By picking up sounds that we cannot hear
What is a recovery unit used for?
To remove the refrigerant from the system and store it in an approved external container without necessarily filtering it processing it in any way,
Service cylinders are, for the most part reusable. True or False?
True
What cylinder color is R-11?
Orange
What cylinder color is R-12?
White
What cylinder color is R-22?
Light green
What cylinder color is R-134a?
Light blue (sky)
What cylinder color is R-410a?
Rose
What cylinder color is R-502?
Light purple (lavender)
What are storage cylinders used for?
For the recovery, recycling, and reclaiming of refrigerant. They are the cylinders that you put the refrigerant into when you remove it from the cooling system.
All storage cylinders must be?
Department of Transportation (DOT) approved
What are vacuum pumps used for?
They are used to evacuate the closed refrigeration system into a deep vacuum. It removes any gas or moisture that may be in the system.
Without a vacuum gauge, you take the risk of not dehydrating the system properly. True or False?
True
A thermistor vacuum gauge contains which two elements?
A heater (filament) and a thermocouple junction that contacts the filament.
What measurement is used for dehydration?
Microns
How many microns do we want to boil and evacuate moisture in a refrigeration system?
500 microns
What are refrigeration charging scales used for?
They are used to weigh in the accurate charge in a refrigeration system.
What are two ways that nitrogen is used in a refrigeration system?
By flowing through copper to prevent it from forming oxides and to pressurize the system to test for leaks.
Liquid in a refrigeration system is what kind of pressure?
High pressure
Vapour in a refrigeration system is what kind of pressure?
Low pressure
Pressure goes from ___ to ___?
High to low
The preferred method of making a strong leak-free joint is?
Brazing with a silver based rod.
What important to do before you braze any pipe?
Fit the pipe and clean it
Oxide forms on copper if?
Air is present
What is our enemy in refrigeration systems?
Oxidation
What is our friend in refrigeration systems?
Nitrogen
What rod is normally used for brazing cooling lines?
An alloy containing 5 to 15 percent silver and is commonly known as Silfos
What should you do after a pipe is brazed?
Apply a wet rag or water to the joint
What test should be done on all field installed systems?
The leak test which is done by filling the system with dry nitrogen.
Laws prevent the release of ___ or ___ into the atmosphere.
CFC or HCFC refrigerants
Where can you identify the type of refrigerant the system contains?
On the equipment rating plate
What is one of the most common ways of compressor failure?
Lack of lubrication or overheating
If components show evidence of icing during the recovery process, what can be done to fix that?
The components can be heated gently to speed up the flow of refrigerant by using a heat gun but never any type of open flame.
What are the two reasons for a proper deep evacuation?
It removes non-condensable gases and it removes moisture.
If you’re using a vacuum pump in a refrigeration system and the gauge rises slowly to 1500 microns, what does this indicate?
That there is moisture in the system and the process must be repeated.
If you’re using a vacuum pump in a refrigeration system and the micron gauge steadily rises to atmospheric pressure, what does this indicate?
That there is a leak and it must be located and repaired.
What steps are done to do a triple evacuation?
Evacuate the system to 1000 microns from both the service valves and hold for two hours, evacuate to 500 microns and hold for 2 hours minimum, and then evacuate the system to the lowest pressure (200 microns for two hours minimum).
What is the reason for taking the system into a perfect vacuum?
As the pressure drops, the temperature at which water evaporates drops as well.
What is super heat?
heat (a liquid) under pressure above its boiling point without vaporization.
What is subcooling?
the difference between condensing pressure/temperature and liquid temperature at the expansion valve inlet.
What is the difference between superheat and subcooling?
While superheat indicates how much refrigerant is in the evaporator (high superheat indicates not enough, low superheat indicates too much), subcooling gives an indication of how much refrigerant is in the condenser.
What do most new split systems come with and how much?
A factory charge of refrigerant and a 15 to 25 feet of line set that is referred to as the default lengh.
What must be done if the actual line set length is greater than the default length for which the manufacturer pre-charged the condenser?
Add refrigerant by weight to account for the actual line set length.
Manufacturers recommend how much CFM per ton of cooling?
400 CFM to 425 CFM per ton of cooling
What are the two most common methods to check for the proper CFM when calculating air flow?
By calculating temperature rise and by calculating static pressure across the evaporator coil.
To calculate the CFM by the temperature rise method you must have?
The furnaces Btuh output, the temperature rise, and the formula CFM = furnace Btuh output divided by (1.08 x temperature rise)
Temperature rise = ?
Supply air temperature - return air temperature
How many readings must you take when using the static pressure method?
Two readings: one before and another after the evaporator coil
When using the superheat chart always get the system down to the lower value and top up as much as you can. True or False?
True
What must you do any time you make an adjustment to the amount of refrigerant in the system?
You must let it run for a minimum of 15 minutes to allow the system to stabilize.
It is much easier to add refrigerant than it is to remove it. True or False?
True
Superheat temperature measurements should be taken within how many feet of the compressor suction line connection?
3 feet
Do not adjust charge based on superheat on systems with thermal expansion valves. True or False
True
What must you do to determine sub-cooling?
Determine the high pressure reading on the gauge, and the temperature of the liquid as close to the evaporator as possible.
Liquid line temperature at the evaporator should be within how many degrees of liquid line temperature at the condensing unit?
2 degrees
Sub-cooling = ?
Saturation temperature - liquid line temperature
