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Evaporator Fan Mystery

When a parallel circuit becomes a series circuit ... Hmmmm

  • Model
  • ED27DQX series
  • Uses Adaptive Defrost Control, p/n 216926
  • Symptoms
  • Very poor cooling
  • if thermostat OFF:
  • compressor OFF, as expected=> good
  • condenser fan OFF, as expected=> good
  • evaporator fan ON! Huh? -----> they're all wired in parallel!! How can this be true???
  • if thermostat set for ANY cooling setting
  • compressor ON, as expected=> good
  • condenser fan ON, as expected=> good
  • evaporator fan OFF! -----> Huh? they're all wired in parallel!! How can this be true???
Control Board
  • ANALYSIS
  • The defrost heater and the evaporator fan return path share a crimp connection going into the wiring harness connector on the neutral side. The connector pin has oxidized and created on open circuit condition between the two sides of the wiring harness connector. This changes the circuit, which normally has the evaporator fan in parallel with the condenser fan and compressor motor, such that the evaporator fan is now in series with the defrost heater and compressor//condenser fan motors. The resistance of the compressor motor and defrost heater is much lower than that of the evaporator fan. The result is that the evaporator fan runs when in defrost mode, but not in cooling mode!! Ahaah!
  • Simplified Circuit (Normal Operation)
  • Evap Mystery 1
  • Simplified Circuit (Fault Condition)
  • Evap Mystery 2

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