UNIT 8 Flashcards
Vacuum below 25 in HG
Deep vacuum
Inert Gas used to pressurize AC systems to leak check, remove contaminants and prevent oxidation while soldering
Nitrogen
Gases that do not change to a liquid when it’s temperature is reduced
Noncondensible gas
Much like the valve stem on an automobile and bicycle tires. Slows the vacuum process and should be removed during evacuation to speed up the process.
Schrader valve
To lower the pressure in a system below the pressure of the atmosphere
Vacuum
Oxygen nitrogen, water vapor, and other noncondensible gases
Contaminants
The last inch of vacuum is measured in this unit of measure
Micron
Reduces atmospheric pressure in a system. Can be single or two stage.
Vacuum pump
To remove refrigerant from the system and store it in an external container, without necessarily testing or processing it in any way
Refrigerant recovery
Used on large systems. Place between the wet system and vacuum pump. Water vapor passes through the container and hits the side of the walls and freezes saving the vacuum pump oil from being contaminated.
Cold trap
Why should you never start a hermetic compressor when it is in a deep vacuum?
Terminal venting
Why is the micron gauge placed as far away from the vacuum pump?
To obtain a more accurate reading
How is acid formed in a system?
Heat + refrigerant + moisture= acid
How does moisture get into a system?
Anytime the system is open, oxygen can easily travel into the system. Oxygen contains elements of moisture.
A micron gauge reads 180 microns. The vacuum pump is valve off and the micron gauge starts to climb. It finally stops at 1500 microns. Is there a leak in the system? explain why the reading increased and stopped rising.
The reason why the reading increased is due to residual trapped underneath the oil such as refrigerant and water. Therefore, it’s not a leak.
A 5CFM vacuum pump can be used on systems up to how many tons?
25 tons
What is the two letter designation on a filter dryer that indicates the filter is used to remove acid from the system?
HH
True or false
A vacuum pump can remove sludge from the system ?
False
True or false
When under a deep vacuum, any trapped water or refrigerant underneath the oil in the compressor can be removed by heating and or beating on the compressor
True
True or false
The oil in the vacuum pump should be changed after each use
False
True or false
Clean refrigerant oil may be used in a vacuum pump
False
True or false
The gas ballast feature on a vacuum pump, reduces the vapor from condensing inside the vacuum pump oil, thereby extending the life of the oil
True
True or false
Acid in a system can break down motor insulation and cause a short circuit or ground to happen
True
True or false
Defrost an evaporator before performing a leak check
True
True or false
The best way to perform a leak test is to pull the system into a vacuum
False
True or false
Oil present at a schrader or access port is a positive sign of a leak
False
True or false
The valves on the gauge manifold need to be open to read the system pressure when the service valves are opened
False
True or false
On systems where the high and low side cannot be isolated from each other, pressurize the system to the lowest pressure listed on the data plate
True
To raise the operating temperature of the system, block the___________
Condenser
When testing a system for combination leaks,___________
All of the above
The suction and discharge valves in a system are positioned in the__________ position for normal operation
Back seated
To stop the flow of refrigerant, flowing into the suction service port from the yellow hose,__________ the low side valve
Front seat
Of the six types of leaks, which one is the rarest or least likely to happen?
Vibration, dependent leaks
When isolating the condenser from outside air currents and to trap refrigerant gas to perform a leak check, what should not be used to prevent false positive readings from occurring?
Plastic sheet/tarp
Which of the following vacuum pumps will produce the lowest vacuum?
9 CFM two stage
The appropriate vacuum pump to use on a 144 ton system is a_______ vacuum pump
12 CFM two stage
What does the check valve in a vacuum pump prevent?
Vacuum pump oil from flowing into the system being evacuated
The best type of hose to use for finding a leak while pulling a vacuum is/are_______
Soft copper tubing
The best manifold to use when evacuating and charging a system without having to disconnect hoses would be the______valve,______hose manifold
4 and 4
If you suspect electroplating has occurred in a compressor, what parts should you check?
All bearing surfaces
What would you use to open a solenoid valve?
A magnet
What are two indicators that your vacuum pump oil needs to be changed?
visual inspection shows oil as cloudy
micron gauge reading, shows numbers above 50 microns
The four things you can do to speed up the evacuation of the system
Use larger, diameter hoses
Use a two stage vacuum pump with highest CFM
Evacuate without manifold
Open all valves
When recovering evacuating and charging refrigerant, what position should all service valves be placed in?
Mid seat
Your system passed the decay test and stayed under 500 microns for a minimum of 10 minutes. You can’t leave the system in a vacuum. What do you do?
Charge the system with nitrogen or refrigerant
Which contactor will not blow the 5A fuse on the low voltage side of the system if the transformer puts out 27VAC?
12 ohm contactor
A transformer puts out 24VAC. It is rated for 40VA. What is the maximum current flow on the output side of this transformer?
1.6A
1/2 “ ACR copper tubing is equivalent to what size nominal copper tubing?
5/8” copper tubing
