Tech method lesson 3A.txt

    • author "me"
    • tags "Cooling 101"
    • description "Diagnosing Refrigerant Circuit"
    • fileName "Tech method lesson 3A"
    • freezingBlueDBID -1.0
    • Tech statement
    • T= temperature controls tells the system to start operating.
    • E= evaporaing unit
    • - evaporator fan must be running in the right direction and at the proper speed.
    • - check blower belts bearings and pulleys.
    • - supply registers must be open and returns cannot be blocked. (Do not adjust dampers)
    • - coil cannot be iced up. If it is then it must be deiced before proceeding.
    • - compute airflow (cfm)
    • C= condensing unit
    • - condenser fan must be running in the right direction and at the proper speed.
    • - coil must be clean.
    • - check for external heat loads. (Ex) dryer vent, recirculation of condenser air, decks etc.
    • - check condenser TD (around 15 ~ 20°)
    • H= heat measurements
    • - measure subcooling and superheat and compare to manufactures specifications.
    • - any inadequacies found and corrected require a recheck of all heat readings to ensure proper operation and that all problems have been found.
    • - many system will have more than one problems.
  1. Superheat
    Heat added to vapor above its boiling or saturation temperature.
  2. Subcooling
    Heat removal from a liquid below its condensing or saturation temperature.
  3. What causes Overcharged
    High subcooling & Low superheat
  4. What causes Restriction
    High subcooling & High superheat
  5. What causes Low on charge
    Low subcooling & High superheat
  6. What cauaes Inefficient compressor / Over feeding metering device
    Low subcooling & Low superheat
  7. What causes Low suction pressure
    • Low airflow across evaporator coil (many reasons)
    • Low on charge
    • Restriction
    • Low indoor (return) air temp.
    • Very low outdoor temp. (Fixed orifice)
  8. What causes High suction pressure
    • High outdoor temp. (Fixed orifice)
    • Airflow too high
    • Overcharged (fixed orifice)
    • High indoor return air temp.
    • Over feeding metering device.
    • Inefficient compressor
  9. What causes Low discharge pressure
    • Inefficient compressor
    • Low outdoor ambient temp.
    • Low on charge
  10. What causea High discharge pressure
    • Non condensables
    • Overcharged
    • High outdoor temp.
    • Dirty outdoor coil / low airflow across condenser
    • Obstruction or recirculation of condenser air
  11. The difference between low on charge & restriction
    • Low on charge:
    • Low suction pressure,
    • High superheat,
    • Low discharge pressure,
    • Low subcooling

    • Restriction:
    • Low suction pressure,
    • High superheat,
    • near or normal discharge pressure,
    • High subcooling.

    • Method:
    • Add small amount of refrigerant to the unit and watch what happen to the gauge. If both pressure moving up proportionaly at the same time, then it is low on charge otherwise it is restriction.
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Tech method lesson 3A.txt