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Evaluating an A/C or Heat Pump System

Evaluating an A/C or Heat Pump System. North Seattle Community College HVAC Program Instructor – Mark T. Weber, M.Ed. This presentation uses an A/C system in its evaluation. However, this same procedure can be used for any type of refrigeration system. First, Hook Up The Manifold Gauge Set.

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Evaluating an A/C or Heat Pump System

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  1. Evaluating an A/C or Heat Pump System North Seattle Community College HVAC Program Instructor – Mark T. Weber, M.Ed.

  2. This presentation uses an A/C system in its evaluation. However, this same procedure can be used for any type of refrigeration system.

  3. First, Hook Up The Manifold Gauge Set Blue line goes to the suction (larger) line Red line goes to the liquid (smaller) line

  4. Second, set thermometers at their locations for evaluation

  5. You’ll need a Digital Psychrometer

  6. Evaluating the Refrigerant Charge • Evaluate Fixed Metering Device Systems by Superheat • Evaluate Thermal Expansion Valves by Sub-cooling

  7. Determine the Required Refrigerant Level ReadingsBrief run-down 1. Determine the Required Superheat 2. Determine the Required Condenser Saturation Temperature 3. Determine the Required Liquid Level in the Condenser 4. Calculate the Operating Superheat

  8. Practice Worksheets • In your course material, there are practice worksheets. Download them and print 5 or 6. • Download and print info sheets. • Pressure Temperature Chart • Refrigerant Troubleshooting Worksheet (Fixed Metering & TXV Systems) • Residential Refrigerant Charging Chart As we work thru these, copy the information in red on the following slides onto one of your worksheets.

  9. In real life, your gauges is where you get the pressures and the saturation temps. These will be provided for this excerise.

  10. Copy the red information on the next slide onto onto your practice sheet.

  11. Air conditioning checklist SEER_10_________ Refrig__R-22__________ Outdoor Unit Model #___XXXXXXXX_______________ Metering device Fixed_X___ TXV________ Determine the Required Readings: Return Air Wet Bulb Temp:__62______ Return Air Relative Humidity:____58% __________ Outdoor Temp:__80_____ + ReqCond Temp :________= Re Cond. Saturation Temp:____________ Req Superheat:________ ReqSubcooling:________ Req Indoor T.D.:____________ Suction Press (PSI):_________ Head Press (PSI):___________________ Suction Line Temp:__________ Cond. Saturation Temp:______________ minus minus Evap. Sat Temp: __________ Liquid Line Temp:___________________ equals equals SUPERHEAT:____________ SUBCOOLING:__________________ Indoor Conditions: Supply Air Temp:____________ Minus Return Air Temp:____________ Indoor Delta T _____________

  12. Worksheet 1. Determine the Required Refrigerant Level Readings 1. Determine the Required Superheat This is a fixed Meter unit. The Return Air Wet Bulb is 62 Outside Air is 80 Use a superheat chart to find the required superheat based on the previous conditions. Make note of this number. It looks like this: Go to next slide.

  13. Outdoor Temp Return Air Wet Bulb Copy this number onto your worksheet

  14. Air conditioning checklist SEER_10_________ Refrig__R-22__________ Outdoor Unit Model #___XXXXXXXX_______________ Metering device Fixed_X___ TXV________ Determine the Required Readings: Return Air Wet Bulb Temp:__62______ Return Air Relative Humidity:____58% __________ Outdoor Temp:__80_____ + ReqCond Temp :________= Req Cond. Saturation Temp:____________ Req Superheat:__12______ ReqSubcooling:________ Req Indoor T.D.:____________ Suction Press (PSI):_________ Head Press (PSI):___________________ Suction Line Temp:__________ Cond. Saturation Temp:______________ minus minus Evap. Sat Temp: __________ Liquid Line Temp:___________________ equals equals SUPERHEAT:____________ SUBCOOLING:__________________ Indoor Conditions: Supply Air Temp:____________ Minus Return Air Temp:____________ Indoor Delta T _____________

  15. 2. Determine the Required Condenser Saturation Temperature We know the SEER of the system is 10. The required TD (Temperature Difference) is 20 degrees. Measure the Condenser Entering Air Temp (O.D. temp). 80 degrees. Calculate the Required Condensing Temp. 80 degrees Plus 20 degrees = 100 degrees Go to next slide

  16. Air conditioning checklist SEER_10_________ Refrig__R-22__________ Outdoor Unit Model #___XXXXXXXX_______________ Metering device Fixed_X___ TXV________ Determine the Required Readings: Return Air Wet Bulb Temp:__62______ Return Air Relative Humidity:____58% __________ Outdoor Temp:__80_____ + ReqCond Temp :__20______= Req Cond. Saturation Temp:__100________ Req Superheat:__12______ ReqSubcooling:________ Req Indoor T.D.:____________ Suction Press (PSI):_________ Head Press (PSI):___________________ Suction Line Temp:__________ Cond. Saturation Temp:______________ minus minus Evap. Sat Temp: __________ Liquid Line Temp:___________________ equals equals SUPERHEAT:____________ SUBCOOLING:__________________ Indoor Conditions: Supply Air Temp:____________ Minus Return Air Temp:____________ Indoor Delta T _____________

  17. Determine the Required Liquid Level in the Condenser Refer to the Charging Chart to identify the required sub-cooling. The unit is SEER 10 so typical sub-cooling is 10 – 15. Split the difference and use 12.

  18. Air conditioning checklist SEER_10_________ Refrig__R-22__________ Outdoor Unit Model #___XXXXXXXX_______________ Metering device Fixed_X___ TXV________ Determine the Required Readings: Return Air Wet Bulb Temp:__62______ Return Air Relative Humidity:____58% __________ Outdoor Temp:__80_____ + ReqCond Temp :__20______= Req Cond. Saturation Temp:__100_____ Req Superheat:__12______ Req Subcooling:__12______ Req Indoor T.D.:____________ Suction Press (PSI):_________ Head Press (PSI):___________________ Suction Line Temp:__________ Cond. Saturation Temp:______________ minus minus Evap. Sat Temp: __________ Liquid Line Temp:___________________ equals equals SUPERHEAT:____________ SUBCOOLING:__________________ Indoor Conditions: Supply Air Temp:____________ Minus Return Air Temp:____________ Indoor Delta T _____________

  19. Here are low side gauge & thermometer measurements 102 72 F Thermometer Low side Gauge Supply air = 59 O.D. Temp = 80 Return Air: Temp = 72 Wet Bulb = 62 R.H. = 58%

  20. Calculate the Operating Superheat • A. Now, we read the gauge. The low-side gauge reads 102 PSIG. Use Pressure Temperature Chart to get temp. For R-22 it is 60 degrees. • The Suction Line actual temp is 72 degrees • Calculate the Operating Superheat • Suction Line Temp 72 degrees • minus Evaporator Saturation Temp 60 degrees • = Operating Superheat 12 degrees • Compare the Operating Superheat to the Required Superheat. • In step 1, we used the chart to determine the Required Superheat and made note of it. It was 12. • Go to next slide to see what your worksheet should look like.

  21. Air conditioning checklist SEER_10_________ Refrig__R-22__________ Outdoor Unit Model #___XXXXXXXX_______________ Metering device Fixed_X___ TXV________ Determine the Required Readings: Return Air Wet Bulb Temp:__62______ Return Air Relative Humidity:____58% __________ Outdoor Temp:__80_____ + ReqCond Temp :__20______= Req Cond. Saturation Temp:__100_____ Req Superheat:__12______ Req Subcooling:__12______ Req Indoor T.D.:____________ Suction Press (PSI):___102___ Head Press (PSI):___________________ Suction Line Temp:____72______ Cond. Saturation Temp:______________ minus This pressure gets you minus this temp from P/T chart Evap. Sat Temp: ____60______ Liquid Line Temp:___________________ equals equals SUPERHEAT:_____12_______ SUBCOOLING:__________________ Indoor Conditions: Supply Air Temp:____________ Minus Return Air Temp:____________ Indoor Delta T _____________

  22. The Operating Superheat is 12 degrees and from our chart we found the ideal to be 12 degrees. With a fixed metering device, plus or minus 5 degrees is acceptable although it is better to be on the + side rather than the – side. Go to next slide.

  23. 5. Measure the Operating Condenser Saturation Temperature 102 PSIG 197PSIG 72 F High-side Pressure Supply air = 59 O.D. Temp = 80 Return Air: Temp = 72 Wet Bulb = 62 R.H. = 58% 80 F

  24. 5. Measure the Operating Condenser Saturation Temperature A. The pressure reading on the High-side gauge is 197 PSIG. B. On the Pressure Temperature Chart, R -22 at 197 PSIG equals 100 – 101 degrees. We’ll use 100 degrees. C. The Liquid line temp is 80 degrees. D. From this chart, for a condenser SEER rating of 10, Typical Cond. TD (Temperature Difference) is 20 degrees. E. Go to your sheet and enter the above numbers

  25. Air conditioning checklist SEER_10_________ Refrig__R-22__________ Outdoor Unit Model #___XXXXXXXX_______________ Metering device Fixed_X___ TXV________ Determine the Required Readings: Return Air Wet Bulb Temp:__62______ Return Air Relative Humidity:____58% __________ Outdoor Temp:__80_____ + ReqCond Temp :__20______= Req Cond. Saturation Temp:__100_____ Req Superheat:__12______ Req Subcooling:__12______ Req Indoor T.D.:____________ Suction Press (PSI):___102___ Head Press (PSI):_________197________ Suction Line Temp:____72______ Cond. Saturation Temp:__100_________ minus minus Evap. Sat Temp: ____60______ Liquid Line Temp:_______80__________ equals equals SUPERHEAT:_____12_______ SUBCOOLING:_____20___________ Indoor Conditions: Supply Air Temp:____________ Minus Return Air Temp:____________ Indoor Delta T _____________

  26. What is your evaluation of this system? This system is operating perfectly. You probably should practice.

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