Mechanical Troubleshooting

1. Chapter 7 Mechanical Troubleshooting

2. 2 Objectives After completing the material in this chapter, the student should be able to: List several common reasons why an air conditioning/refrigeration system may fail. List some reasons why refrigerant escapes from a refrigeration system. Identify the effects of a defective condenser fan motor on system operation. Identify the effects of a defective evaporator fan motor on system operation. Explain how a system overcharge affects system operation.

3. 3 Objectives After completing the material in this chapter, the student should be able to: Explain how a refrigerant undercharge affects system operation. Explain the importance of a correctly mounted thermostatic expansion valve thermal bulb. List the seven steps in performing a successful service call. Perform a service call utilizing the seven-step method. Determine if an air conditioning system has an overcharge of refrigerant.

4. 4 Objectives After completing the material in this chapter, the student should be able to: Remove refrigerant from an overcharged air conditioning system. Determine if an air conditioning system has a refrigerant undercharge. Add refrigerant to an undercharged air conditioning system.

5. 5 Evaporator and Condenser Fan Motor Problems Improper airflow Improper lubrication Improper pulley alignment Improper belt tension

6. 6 Improper Airflow Condenser airflow: Dirty condenser coil Blocked condenser coil Evaporator airflow: Dirty air filter Dirty evaporator coil Defective evaporator fan motor Blocked supply registers

7. 7 Improper Airflow (A) Forward-curve centrifugal blower and housing assembly. (B) Dirt accumulations on the blades of the blower reduces the blower�s ability to move air.

8. 8 Improper Airflow Low overhangs can cause the discharge air from the condensing unit to recirculate through the coil.

9. 9 Improper Pulley Alignment Uneven belt wear. Excessive belt breakage. Belts coming loose from the pulleys without braking.

10. 10 Improper Pulley Alignment Pulleys must be aligned properly.

11. 11 Refrigerant Charge-Related Problems Excessive refrigerant charge: High condenser subcooling Low evaporator superheat (except on TXV systems) High temperature differential across evaporator coil Low refrigerant charge: Low condenser subcooling High evaporator superheat (except on TXV systems) Low temperature differential across evaporator coil

12. 12 Low Refrigerant Charge Can result from system undercharge or system leak Methods of leak detection: Audible hiss Using liquid leak detector or bubble solution Using a halide leak detector Using an electronic leak detector Using an ultraviolet (UV) light

13. 13 Non-Condensable Gas Typically air or nitrogen. Cause system pressures to be higher than normal. Reduce system efficiency.

14. 14 Excessive Superheat Can be caused by: Refrigerant undercharge. Improper superheat spring setting on the thermostatic expansion valve. Blocked or clogged strainer on the thermostatic expansion valve. Blocked or clogged capillary tube. Blocked or clogged strainer at the capillary tube inlet. Indoor fan motor speed too high.

15. 15 Low Superheat Can be caused by: Refrigerant overcharge Overfeeding metering device Improper superheat spring setting on the thermostatic expansion valve Improperly mounted thermostatic expansion valve thermal bulb Restricted airflow across the evaporator (blocked coil or inoperative fan motor) Dirty air filters Reduced water flow through the evaporator (chiller applications)

16. 16 Low Superheat Proper positions for TXV thermal bulb (Courtesy of Alco Controls).

17. 17 Low Subcooling Can be caused by: Dirty or blocked condenser coil Defective condenser fan motor Service panels removed from condensing unit Reduced water flow through the condenser (water-cooled applications) Defective water-regulating valve (water-cooled application)

18. 18 Excessive Subcooling Can be caused by: System operating in low ambient conditions Refrigerant-flow restriction Non-condensable gas in the system Overfeeding water-regulating valve (water-cooled applications)

19. 19 Troubleshooting Steps Verify the complaint. Gather information. Perform a visual inspection. Isolate the problem. Correct the problem. Test the system operation. Complete the service call.

20. 20 Summary Motor problems can result from improper airflow, lubrication, pulley alignment, or belt tension. A refrigerant overcharge or undercharge can cause reduced system efficiency and cooling capacity. Gauge manifolds must be installed and removed properly to reduce the possibility of allowing atmosphere to enter the system. Refrigerant leaks can be caused by rubbing or vibrating surfaces or poor quality soldering or brazing.

21. 21 Summary Refrigerant leaks can be located by audible noise, bubble solutions, electronic leak detectors, halide torches, or UV light. Non-condensable gases, such as air and nitrogen, increase operating pressures, reduce system performance, and reduce cooling capacity. A vacuum gauge should be used during system evacuation to ensure that proper vacuum levels are reached. Excessive evaporator superheat reduces cooling capacity.