The normally closed evaporator overload feedback relay opens between terminals 5 & 9 when either the supply fan has been physically blocked or when it does not receive the correct power (208/230VAC +/- 10%). This alarm also serves as a warning when no power is applied to the WPU.  

Note: Evaporator Overload alarm only applies to AC powered supply fans. If this alarm is displayed when the power supply for the fan is DC, change the fan setting SF1 in D menu from 1 to 0 or from AC/AUT to DC. If using the PGD, change option Ch1 in the Manufacturer Menu to DC. See Chapter 1: Model Identification to determine supply fan power input.


Possible Cause
Component to Check
Recommended Action
No power input to the system
Verify 208/230VAC at the input breaker (QF)
Turn on breaker/power supply.
Correct wiring.
No power input to the supply fan
Verify 208/230VAC across wire 401/402 for 5 Ton model, 401/L for 13 wire models (non-5 Ton), and 400/L for ALL Cat5 models.

Verify Evap. Fan
Correct wiring.
Replace fan relay (KA1) if faulty.
Loose/incorrect feedback wiring
Alarm wiring
Refer to the Fan Overload Alarm Wiring diagram.
Faulty overload switch
Normally closed overload output (two white wires coming from the supply fan)
If 208/230VAC is verified going into the supply fan and the two white wires connecting to 5 and 9 are still open, replace the fan.

Fan Overload Alarm Wiring