Understanding Refrigeration Systems: Types, Components, and Recovery Procedures, Exams of Nursing

Download Understanding Refrigeration Systems: Types, Components, and Recovery Procedures and more Exams Nursing in PDF only on Docsity! 1 [Date] 1 HVAC- EPA 608 Certification Study Guide 100 Questions & Answers 2024 Are there drop-in replacements for R-12 systems? Why or why not? - Correct answer No because the new refrigerants are incompatible with the oils and lubricants used in R- 12 systems. What type of oil is used in R-134a and what oils will it mix with? - Correct answer Ester based oils and they do not mix with other oils What type of lubricant is used with HCFCs? - Correct answer Alkyl benzene lubricant What is difference b/w ternary blend an isotropic blend? - Correct answer Ternary blends are three-part mixtures whereas azeotropic blends are blends of two or more compounds that act like a single compound. What is the trait of a hygroscopic lubricant? - Correct answer it absorbs (takes on) moisture What is temperature glide and what type of blend won't have it? - Correct answer Temp. blend is the difference between the dew point and the bubble point Dew Point - Correct answer Occurs when saturation temp in evaporator causes refrigerant to change from liquid to vapor Bubble Point - Correct answer occurs when saturation temp in condenser changes refrigerant from vapor to liquid 2 [Date] 1 Will the gases in a ternary blend leak at the same rate? Why or why not? - Correct answer No because different refrigerants in blend have different vapor pressures, causing them to leak at uneven rates Refrigeration Process - Correct answer transfer of heat from one place to another Evaporator - Correct answer Absorbs heat into system from space to be cooled. Absorption of heat causes refrigerant to boil. Upon leaving, refrigerant changed to low pressure, low temperature vapor Compressor - Correct answer Takes low pressure, low temp vapor and changes it to a high-temp, high-pressure, superheated vapor and delivers it to the condenser Condenser - Correct answer Rejects heat from system and changes refrigerant from high-temp, high-pressure vapor into high-pressure, high-temp liquid Metering Device - Correct answer reduces pressure of refrigerant and changes the high-pressure, high-temp liquid into low pressure, low temp liquid. Compound Gauge - Correct answer typically blue and measures low pressure (psig) and vacuum (night). High Pressure Gauge - Correct answer Red and measures high side (discharge) pressure. 0 to 500 psi What does a compressor compress? - Correct answer Vapor Why will refrigerant migrate to the crankcase in a compressor? - Correct answer Because of the vapor pressure difference between refrigerant and oil What color is the high pressure gauge? - Correct answer Red 5 [Date] 1 Low-loss Fittings - Correct answer can be manually or automatically closed when disconnecting hoses in order to prevent refrigerant loss Service Aperture - Correct answer typically straight piece of tubing that is entered with piercing access valve Find the pressure for R-12 at 80 degrees F. - Correct answer 84.4 psi Find pressure for R-22 at 70 degree F. - Correct answer 121.4 psi R-134A at 90 degree F - Correct answer 104.3 psi What might happen if cylinder containing mixed refrigerants is given to reclamation center? - Correct answer Refuse to process it and ship back to sender or destroy it for a substantial fee What is difference between self-contained recovery tank and system-dependent recovery tank? - Correct answer a self-contained recovery tank uses its own power to recover refrigerant from systems and is capable of reaching required recovery rates with or without compressor operating. Stores in pressurized tank. A system-dependent recovery tank captures refrigerant into a non-pressurized container. Uses system's compressor, an external heat source, or vacuum pump to recover refrigerant. What are two things that can cause high discharge pressures? - Correct answer not opening tank inlet valve or having excess air will cause higher discharge pressures 6 [Date] 1 How can you check if a tank contains excess air or non-condensable? - Correct answer Check pressure inside recovery tank after allowing temp of cylinder to stabilize to room temperature What type of system can a vacuum pump be used on for recovery? - Correct answer a vacuum pump can only be used on a recovery device in combination with a non- pressurized container and cannot be used with self-contained recovery equipment (pressurized container) When using a system-dependent recovery system with an operating compressor, where should the refrigerant be recovered from? With a non-operating compressor? - Correct answer when using a system-dependent recovery process with an operating compressor, run the compressor and recover from the high side of the system. When using a non-operating compressor, it may be necessary to access both low and high side of system to achieve required recovery level and it will speed the recovery How can you release trapped refrigerants in the oil? - Correct answer Necessary to heat and tap compressor with mallet several times or use vacuum pump How will activating a defrost timer aid in recovery process? - Correct answer Help vaporize any trapped liquid refrigerant When should piercing type valves be used? What is a common problem with these valves? - Correct answer Copper or aluminum tubing only. Tend to leak over time What are some other small refrigeration systems that contain other types of refrigerants? Should these refrigerants be recovered with standard EPA equipment? - Correct answer Ammonia, hydrogen or water and therefore, should not be recovered using current EPA-approved recovery devices. Similarly, systems built before 1950 may 7 [Date] 1 have methyl format, methyl chloride, or sulfur dioxide as refrigerants and require special recovery equipment What should be done before charging a new system with refrigerant? - Correct answer the unit should first be pressurized with NITROGEN (inert gas) and leak checked What are the leak repair requirements for comfort cooling appliances and commercial appliances containing 50 pounds or more of refrigerant? - Correct answer the leak rate exceeds 15% in comfort cooling appliances The leak rate exceeds 35% in all commercial and industrial process refrigeration Using large vacuum pumps can lead to freezing of water in the system. What are two ways the technician can help prevent freezing? - Correct answer Increase pressure by introducing nitrogen to counteract freezing. Liquid charging of an R-12 refrigeration system should begin with vapor from a vacuum level to a pressure of approximately 33 psig followed by a liquid charge through the liquid-line service valve. Foaming at start-up may be found in what component? What does this mean? - Correct answer Refrigerant in the oil will cause oil foaming in the compressor at start-up When evacuating a vapor compression system how many microns does the vacuum need to achieve? - Correct answer 500 microns (or 29.90" Hg) Why should you never start a hermetic compressor when under deep vacuum? - Correct answer the motor winding could be damaged if energized What is a receiver? Where is it located and what is the state of the refrigerant after leaving the receiver? - Correct answer Systems using thermal expansion valves will have a receiver/tank on the outlet side of the condenser, designed to hold liquid refrigerant. 10 [Date] 1 Where should you remove the refrigerant in a system that has a condenser below the receiver? - Correct answer Condenser outlet How must you recover refrigerant from a parallel system? Why? - Correct answer Isolate a parallel compressor system in order to recover refrigerant. Failure to isolate a parallel compressor system will cause an open equalization that will prevent refrigerant recovery Where do leaks commonly occur in low pressure systems? What about open-drive type compressor systems? - Correct answer Leaks in gaskets or fittings. The SHAFT SEAL in open-drive compressor low pressure refrigeration systems is particularly susceptible to leaks Does refrigerant go out of the system in low pressure or does air and moisture go in? Why? - Correct answer A low-pressure system operates in a vacuum (below atmospheric pressure) to enter the refrigeration system. When a low pressure system should be leaked checked according to ASHRAE guideline 3-1996? - Correct answer if the pressure in system rises from 1 mm Hg to a level above 2.5 mm Hg during vacuum testing What does a purge unit do and what is a high efficiency purge unit? - Correct answer the purge unit prevents the accumulation of non-condensable substances (air and moisture) in order to keep the system clean and maintain efficiency. The purge unit removes air and moisture to prevent reduced condenser surface area, increased head pressure, compressor surge, increased pressure differential, and system corrosion. A high efficiency purge system will expel very little refrigerant along with the air. 11 [Date] 1 How does a centrifugal purge unit work? - Correct answer a centrifugal purge unit takes its suction from the top of the condenser, removes the air from the system, and returns the refrigerant to the evaporator. What are three visible ways to check for leaks in a low pressure system? - Correct answer Excessive running of a purge system, continuous excessive moisture in the purge unit could indicate a leak in the condenser or the chiller barrel, high lead pressure. What needs to be done to leak check a low pressure system? - Correct answer Increase the pressure in the system by use of controlled hot water or heater blankets. What can happen if you exceed 10 psig while pressurizing the system? - Correct answer can cause the rupture disc to fail How should a water box be leak tested? - Correct answer is certain water has been removed, and then places the leak detector probe in through the drain valve. What equipment should be used to leak test a tube? - Correct answer Hydrostatic tube test kit What are the leak repair requirements for comfort cooling appliances and commercial appliances containing 50lbs. or more of refrigerant? - Correct answer the leak rate exceeds 15% in comfort cooling appliances or the leak rate exceeds 35% in all commercial and industrial process refrigeration What are the typical pressure settings for rupture discs on low pressure systems and recovery equipment? - Correct answer the rupture disc on a low pressure system is set for 15 psig while the recovery unit's high pressure cut-out is typically set for 10 psig in order to help prevent damage to the low pressure 12 [Date] 1 How should a technician recover refrigerant from a system using R-11 or R-123? - Correct answer Remove the liquid first and recover the remaining vapor After removal of liquid, about how much vapor will remain in the system on a 350 ton R- 11 chiller? - Correct answer 100lbs How can you speed up the vapor recovery process on Type III systems? - Correct answer a heater on the recovery vessel side will help evacuate the vapor faster Where does the water typically come from in a water cooled condensing system? - Correct answer Municipal water supply What parts of the system should be drained of water before recovering refrigerant? - Correct answer the water sides of the evaporator and condenser should be drained prior to recovering the refrigerant How should a technician treat the oil before removal and why? - Correct answer a temperature of 130 degrees F should be attained first. Why should you never change liquid refrigeration into a deep vacuum? - Correct answer Causes the refrigerant to boil and may lower the temperature enough to freeze the water in the tubes. At what point in the system should you charge a low pressure system and what should you start the charge with? - Correct answer Charge through the evaporator charging valve as this is the lowest point on a low pressure system. First charge the system with vapor until the refrigeration saturation temperature reaches 36 degrees F or the vapor pressure reaches 16.9" Hg vacuum What are the levels of evacuation for low pressure systems for equipment manufactured before 11/15/1993? How about after 11/15/1993? - Correct answer 25" Hg for before