Hvac Flashcards
What are flaws?
Exist at every joint fitting, seam, or weld
Flaws may be too small to detect but given time, vibration, temperature, and environmental stress, these flaws become larger detectable leaks
What can flow under layers of paint, flux, rust, slag, and pipe insulation?
Vapor
Vapor can flow under layers of paint, flux, rust, slag, and pipe insulation
What is important to do at the leak site?
Clean the leak site by removing loose paint, slag, flux, or rust
It is important to clean the leak site by removing loose paint, slag, flux, or rust
Besides loose paint, slag, flux, or rust, what else must be removed at the leak site?
Pipe insulation, oil, and grease
Must also remove pipe insulation, oil, and grease to avoid contaminating the detection tips
Standing leaks
Detected while the unit is at rest or off
The most common of all leaks
Pressure dependent leaks
Detected as the system pressure increases
Pressure dependent leaks
Temperature-dependent leaks
Associated with the heat of expansion
Temperature-dependent leaks
What is the first step in performing a standing pressure test?
Pressurize the system with dry nitrogen to a pressure no higher than the lowest system test pressure
Example: Pressurize the system to 100 psi
What is the second step in performing a standing pressure test?
Allow the system to rest for ten minutes
No additional information
What is the third step in performing a standing pressure test?
Mark the needle positions on the gauge manifold
No additional information
What is the final step in performing a standing pressure test?
Monitor gauge needle position
No additional information
Vibration-dependent leaks
Occur during unit operation
Vibration-dependent leaks occur during unit operation.
Combination-dependent leaks
Require two or more conditions to leak
Combination-dependent leaks require two or more conditions to leak.
Cumulative microleaks
All the individual leaks that are too small to detect with standard tools
Cumulative microleaks refer to all the individual leaks that are too small to detect with standard tools.
What can vapor flow under at the leak site?
Vapor can flow under layers of paint, flux, rust, slag, and pipe insulation
Example sentence: Vapor can flow under layers of paint, making it important to properly clean the leak site.
Why is it important to clean the leak site?
So system is more efficient
What else must be removed from the leak site?
Must also remove pipe insulation, oil, and grease to avoid contaminating the detection tip
Additional information: Removing pipe insulation, oil, and grease helps maintain the integrity of the detection process.
What does air contain?
Oxygen, nitrogen, and water vapor
Air contains oxygen, nitrogen, and water vapor
What is nitrogen?
A non-condensable gas
Nitrogen is a non-condensable gas
What do non-condensables cause?
A rise in the system’s operating head pressure
Non-condensables will cause a rise in the system’s operating head pressure
What do oxygen and water vapor cause in the system?
Chemical reactions
Oxygen and water vapor cause chemical reactions in the system
What do oxygen and water vapor produce in the system?
Acids that deteriorate system components, electroplating of the running gear, and the breakdown of motor insulation
Produce acids that deteriorate system components, electroplating of the running gear, and the breakdown of motor insulation
Is repairing leaks usually as economical as adding refrigerant?
No, repairing leaks is usually not as economical as adding refrigerant.
Example sentence: It is often more cost-effective to simply add refrigerant instead of repairing leaks.
What is the best field practice when it comes to system leaks?
The best field practice is to repair system leaks whenever possible.
Additional information: Repairing leaks helps maintain system efficiency and prevents environmental harm.
Who establishes requirements regarding when leaks must be repaired?
The EPA (Environmental Protection Agency) establishes requirements regarding when leaks must be repaired.
No additional information provided.
What factors may determine when leaks need to be repaired?
The factors that may determine when leaks need to be repaired include the type of system, refrigerant used, and/or total system charge.
No additional information provided.
Systems with Schrader Valves take longer to evacuate than systems with service valves
Field service valves are used to replace Schrader valve stems while the system is under pressure
Schrader valve caps should be put back on the valve after service
What do chemical combinations create?
Hydrofluoric or hydrochloric acids
Example sentence: Chemical combinations can create hydrofluoric or hydrochloric acids.
What does evacuation consist of?
Degassing + dehydration
None
What does moisture + acid + oil result in?
Sludge
None
What can sludge cause in system components?
Plugged components
None
What can proper evacuation eliminate?
Formation of acid and sludge
None
TEV or TXV (Thermostatic Expansion Valve)
Measuring and adjusting superheat
Mounting the sensing bulb
Use on multi-circuit evaporators
Identification and application
AEV (Automatic Expansion Valve)
EEV (Electronic Expansion Valve)
Fixed Metering Devices
Pistons and capillary tubes
Primary function of a TEV
Maintain superheat
TEV stands for Thermostatic Expansion Valve
Opening force/liquid line temp
Bulb pressure
Opening force is generated by the pressure in the sensing bulb
Closing forces
Evaporator pressure
One of the closing forces is generated by the evaporator pressure
The TEV closes when the evaporator pressure is too low
Closing forces
Adjustable spring
Another closing force is provided by an adjustable spring
Notes for the next slide
Assume an R22 system, and
There is R22 in the sensing bulb
These notes are important for understanding the operation of the TEV
Measuring Superheat
• Superheat =
Suction line temperature – Evaporator temperature
•
High superheat:
–
Evaporator is “Starving”
• Because all liquid has boiled off too soon
•