- Austin, TX 78736
- 9217 Hwy 290 W STE 200
Evaporator Fan Mystery
When a parallel circuit becomes a series circuit ... Hmmmm:
Here's an interesting case of an evaporator fan that seems to be on when it should be off and vice versa.
- ED27DQX series
- Uses Adaptive Defrost Control, p/n 2169267
- very poor cooling
- if thermostat OFF:
- compressor OFF => good
- condenser fan OFF => 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 => good
- condenser fan ON => good
- evaporator fan OFF! -----> Huh? they're all wired in parallel!! How can this be true???
The Adaptive Defrost Control Board:
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!!
Simplified Circuit (Normal Operation):
Simplified Circuit (Fault Condition):
Oak Hill Appliance