Tech method lesson 1a.txt

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Tech method lesson 1a.txt
2013-05-24 06:49:32


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    • author "me"
    • tags "Cooling 101"
    • description ""
    • fileName "Tech method lesson 1a"
    • freezingBlueDBID -1.0
    • Tech method (introduction)
    • Faulty / incomplete diagnosis is the underlying cause of most callback. Callbacks are the #1 enemy of the service technician.
    • Callbacks eat up profits and destroy the reputation of both the service technician and contractor.
    • Diagnosing systems is a process of elimination.
    • Eliminate those portions of the system that are operating properly.
    • You must be able to identify proper operation.
    • T = temperature controls
    • E = evaporating unit
    • C = condensing unit
    • H = Heat measurements
  1. T = temperature controls
    • Temperature controls can be electric electronic or pneumatic.
    • Nothing happens until the temperature controls tell the system to start. This makes it the ideal place to start.
  2. E = evaporating unt
    • Evaporating unit consists of coil, fan, and duct work.
    • Any obstruction system operation and will confuse your diagnostic efforts.
  3. C = condensing unit
    • Condensing unit consist of the outdoor coil, fan, compressor.
    • Inadequate outdoor airflow will cause confusing symptoms to appear in various parts of the system.
  4. H = heat measurements
    • Superheat & sub cooling measurements are most accurate under design conditions.
    • In cold ambient conditions it is necessary to raise the condensing temperature to at least 100 degrees before taking these measurements.
  5. Excessive sub cooling caused by:
    • Non-condensables (air)
    • Overcharged
    • Restriction (normally at metering device)
  6. Note:
    • TXV; charge refrigerant through subcoolng.
    • Fixed Orifice; charge refrigerant through superheat.
  7. High superheat (based on txv/fixed orifice)
    • High superheat caused by;
    • Undercharge (leak),
    • Restriction
  8. Low superheat (based on fixed orifice)
    • Low superheat is caused by;
    • Overcharge (fixed orifice),
    • Over feeding metering device (txv/fixed orifce),
    • Inefficient compressor (fixed orifice)
  9. Note;
    • Low airflow gives low superheat,
    • High airflow gives high superheat.