Refrigeration Servicing

Refrigeration Servicing 2011

Answer the questions using the text references noted in the student study notes. For example, IM is the abbreviation for Industrial Maintenance, 3rd edition HVACR 201 is (HVACR).

Answer the questions in your own words. Not all the answers are found in these texts but will be discussed in the pod casts and/or demonstrated in lab activities at the seminar.

Refrigerant Handling Safety

1. What happens to pressure inside a cylinder or a refrigeration system when a refrigerant is heated?

2. When a large pressurized cylinder is moved what safety precautions MUST be taken?

3. What is the approved method for moving a pressurized cylinder?

4. What is the purpose of a fusible plug or rupture disc on a pressurized cylinder?

5. Sketch the approved method for heating a refrigerant cylinder.

6. What two pieces of personal protective equipment will you use when working around refrigerant that could be released as the work proceeds?

7. Why MUST nitrogen pressure be regulated while being used?

8. What precautions MUST you take when working in cool or cold spaces?

9. What serious problems can occur if refrigerant gas leaks?

10.Why are refrigerant monitors placed in refrigerant storage areas?

11.Why must the fire department know about the amounts and types of refrigerants stored in your facility?

12.What precautions MUST be taking when handling chemicals or used refrigerant oil?

1 MECHANICAL REFRIGERATION CYCLE 1. Define refrigeration. (IM p. 195) 2. Sketch and describe the basic operation of a mechanical refrigeration cycle. State what the various parts do. Sketch and describe the state of the refrigerant in each section of the refrigerant cycle. Sketch in the division points. (IM Fig 6-2 p.196)

THEORY 1. What is temperature? (IM p. 195) 2. What is the definition of a BTU? (IM p. 68) 3. Define heat and cold. (IM p. 76-78) 4. In which direction does heat always move? (IM p. 77) 5. What is the law of the conservation of energy? 6. What three factors determine the rate at which heat will flow? 7. Sketch and describe the movement of heat through conduction, convection, and radiation in a home air conditioning system. (IM p. 677-78) 8. What is forced convection? 10. What is sensible & latent heat? (IM p. 239) 11. Where does a refrigeration system absorb and reject latent heat? 12. 1 lb of ice at 32F will take 144 BTUs to melt to water at 32F. To raise one lb of water from 32F to 212F will take 180 BTUs per lb of water. 1 lb of water at 212F needs 970.4 BTUs to change the water to steam at 212F. If steam is heated above 212F sensible heat is added (superheat). (HVACR p. 322, Fig 13-7) 13. One ton of refrigeration effect is 28800 BTU/day, 12000 BTU/hour, and 200 BTU/minute (HVACR p. 319-322).

PRESSURE 1. What is atmospheric pressure at sea level? How high up will atmospheric pressure at sea level push a column of mercury?

2 2. What is gage pressure, pounds per square inch gage, psig? 4. What is absolute pressure, psia? (0 pisg = 14.7 psia at sea level) 5. How is vacuum expressed in refrigeration terms? Complete vacuum = 29.92 in. Hg vacuum = 0 microns = 0 psia. 6. What happens to saturation temperature of a refrigerant as pressure increases and decreases? 7. What happens to pressure and volume of a gas if you increase temperature of the gas in a confined space? 8. Why should you not heat a can of refrigerant, an evaporator, or a condenser, with a torch or other extreme heat source? 9. If you know the pressure in the evaporator or condenser what else do you know? 10. If you know the temperature in the evaporator or condenser what else do you know? 11. What happens to the pressure of a refrigerant if air or another gas is mixed into the refrigerant? 12. Why do you need a high and low-pressure side to make a refrigeration system work properly? 13. When will you use a refrigerant pressure temperature chart? 14. Check the refrigerant pressure temperature chart to determine these values (HVACR Fig 13-7, p. 42)

HFC-134a boils at 15°F at atmospheric pressure, at69°F at 70 psi, and 112°F at 150 psi. CFC-22 boils at 41°F at atmospheric pressure, at 44°F at 70 psi, and 83°F at 150 psi.

COMPRESSORS 1. What is the purpose of a refrigeration compressor? How does a compressor compress a gas? (HVACR p. 12; IM p.198) 2. What is the difference between a hermetic compressor and a semi hermetic

3 compressor? (HVACR p. 12; IM p.198) 3. List three general refrigeration compressor types. 4. What is the compression ratio of a compressor? What is the problem with a high compression ratio? 5. What maintenance rules apply to refrigerant oils? 6. What problems are caused when too much oil is carried in the refrigerant when it leaves the compressor? (HVACR p. 35) 7. What is foaming and how is it prevented? (HVACR p. 36) 8. What maintenance do compressors require? 9. Why should you not try to convert a refrigeration system from medium or high temperature to low temperature operation? 11. How will you clean-up after a compressor burnout? (IM p. 188)

EVAPORATORS 1. What is the purpose of an evaporator? (HVACR p. 146) How will you determine the low side saturation (boiling temperature) in an evaporator called? 2. Why must an evaporator be colder than the surrounding air in the cooled space? 3. How does an evaporator remove moisture from the air? (RT 21.6, p. 404) 4. Sketch and describe the operation of a dry type of evaporator under normal load. (HVACR Fig. 1-7, p. 147; IM Fig 6-14 p. 200) 5. Describe what is meant by superheat. (HVACR Fig 7-3, p. 148) 6. What is relative humidity and dew point? How does ice form on an evaporator? 7. (HVACR p. 148 & 149) 8. Describe the on-off method of defrosting.

9. Sketch and describe a hot gas by-pass defrost. (IM Fig 6-15 p. 206) 10.What maintenance do evaporators require? 11.What is a hot pull down and what problems can this cause when troubleshooting? (HVACR p. 163)

4 12.What is the Seasonal Energy Efficiency Rating? (HVACR p.23, 187. 323-324, 428) 13.What do we mean by temperature difference or Delta T in evaporators? (RHVAC pl 160 & 164) 14.Describe the operation of a flooded evaporator (HVACR pl. 146 & 149).

LEARNING RESOURCES: 1. IM p. 193-195

CONDENSERS What is the purpose of a condenser (HVACR p. 5-58; IM p. 201) Sketch and describe the operation of an air-cooled condenser. (HVACR Fig. 4-2 & 4-3 p. 57-62 ; IM Fig 6-6 p. 201 ) Describe the operation of a low ambient temperature head pressure control. What is the purpose of this control? (HVACR p. 70 - 72) What is subcooling in a condenser? (HVACR 92-93) Briefly describe the operation of these water cooled condensers: tube within tube, shell and coil condenser, and shell and tube condenser. (HVACR p. 72-77; IM p. Fig 8-7 p. 202 ) Describe the operation of an evaporative condenser. (HVACR p. 78-79; IM Fig. 6-8 p. 202 ) What maintenance do condensers require? (IM p. 202)

Metering Devices What is the purpose of a metering (expansion) device? (HVACR p. 86; IM p. 203) Describe the general operation of a thermo-expansion valve as it opens and closes. What condition is this valve trying to maintain? (HVACR p. 87-89; IM Fig. 6-11 p. 204 ) Why do you generally want a ball park figure of 10 °F of superheat in an evaporator? Describe the pressure temperature method for determining superheat. (HVACR p.92- 93; IM p 231 )

5 Describe how to attach a sensing bulb correctly to piping. (HVACR p. 106 )

Describe the operation of an electrically controlled expansion valve and where it might be used. (HVACR p111-114) Describe the operation of an automatic expansion valve and in what type of application it will be used. (IM Fig 6-12 p 205) Describe the operation of a capillary tube. (HVACR p. 95-97; IM p. 204) What maintenance will expansion devices require? Describe the operation of a fixed orifice metering valve.

LEARNING RESOURCES: 1. IM Metering Devices p. 191 - 193

LEAKS 1. Describe the procedure for finding the general location of a leak then pinpointing the leak detector. (HVACR p. 168 - 169; IM p. 228 - 229 ) 2. How is a standing pressure test conducted? (HVACR p. 170; IM p. 228 ) 3. Describe how to use an electronic leak detector. (HVACR p. 141 &170) 4. What visual signs might you find at the location of an oil leak? 5. Why check any service ports when leak testing?

SYSTEM SERVICE VALVES When are piercing valves used? (HVACR p. 125) When will the service valve be in the back-seated position for an in-line service valve? (HVACR p. 123; IM Fig. 6-26 p.221) When will the service valve be in the mid-seated position for an in-line service valve? (HVACR p. 123; IM Fig. 6-26 p.221) When will the service valve be in the mid-seated position for an in-line service valve? (HVACR p. 123; IM Fig. 6-26 p.221) When will the service valve be in the cracked position for an in-line service valve? (IM

6 Fig. 6-27 p.221) Describe the operation of an access port. Describe the operation of a Schrader valve. (HVACR p. 122) How can a Schrader valve be removed from a system? (HVACR p. 125)

GAGE MANIFOLDS Sketch the front-seated and back seated positions for a three-hose gauge manifold. (IM Fig 6-25 p. 220) How do you disconnect a gauge manifold so that most of the refrigerant in the hoses will not be lost? (Seminar) What care do gage manifolds require? (Seminar) Describe a four-hose manifold. (IM Fig 6-25 p. 220 & seminar) Sketch and describe how to take system pressure readings using a three-hose gauge manifold. (IM Fig. 6-27 p. 222) What advantages are there in using low loss fittings for gage manifold hoses? How can you retrofit old-style, open-ended hoses to be low-loss hoses?

SYSTEM EVACUATION

1. Sketch the positions for a three hose manifold for evacuating a system. Sketch and describe how an evacuation will be conducted. (HVACR p. 174 IM p. 227) 2. Why must we make a complete evacuation before charging a system? (HVACR p. 175) 3. What two types of acids are formed in a 134a system? 4. What is the boiling point of water at sea level, at 20.80 in Hg vac, at 29.82 in Hg vac, and at 29.99 in Hg vac? (HVACR Fog 8-1 p. 175) 5. What is the reason for pulling a deep-vacuum on a refrigeration system? What micron reading is considered a deep vacuum? (HVACR p. 176 IM p. 228) 6. How many microns in one inch? What device is used to measure microns? 7. What happens to a micron gage reading system pressure when the vacuum

7 pump is shut off? What happens if there is still moisture or refrigerant in the system? What happens if there is a leak in the system? (seminar) 8. Why must vacuum pump oil be changed on a regularly scheduled basis? (HVACR p. 176- 180) 9. Why must vacuum pump oil containers and vacuum pumps be securely capped when not in use? 10.What happens if a vacuum pump is shut off improperly? 11.Why is vacuum leak detection not accurate? 12.Where can moisture be trapped in a system? How can it be removed during evacuation? 13.How will a contaminated system be cleaned? 14.Why should Schrader valves be removed when evacuating or charging a system? How are these valves removed? (HVACR p. 180 & 122) 15.Describe the general method of testing refrigerant for oil and moisture contamination. (seminar)

REFRIGERANT CHARGING 1. Sketch and describe the hose and valve positions for liquid and vapor charging a system. (HVACR Fig. 15 p. 184 IM Fig 6-35 p. 230) 2. Why might liquid refrigerant stop flowing into a system before it is fully charged? 3. How can you warm a refrigerant can? Why might you warm a refrigerant can? 4. Why might you have to bypass the low pressure control when charging a system? 5. When might you liquid charge into the low side? How can you accomplish this without damaging the low side? 6. Describe the general process of charging a system by weight. 7. Describe the general process of charging a system by determining superheat or subcooling. (HVACR p. 186 & 189; IM p. 231) 8. Describe the general process of charging a system using a charging chart. (HVACR p. 193; IM p. )

8 9. List three other conditions to consider when charging a system. (HVACR p. 193)