Bosch EC Series - Page 41

Troubleshooting
Unit Troubleshooting
Problem Possible Cause Action
Blower operates but
the compressor does
not
Thermostat/
Controller (DDC)
Check settings, calibration, and wiring.
Wiring Check for loose or broken wires at compressor, capacitor, or contactor.
Safety Controls Check the UPM board red default LED for blink code.
Compressor
Internal Overload
Open
If the compressor is cool and the overload will not reset, replace the compressor.
Compressor
External Overload
Open
If the compressor is cool and the external compressor overload will not reset, then replace the external
compressor overload.
Compressor Motor
Grounded
The internal compressor winding is grounded to the compressor shell. Replace the compressor. If the
compressor is burnt out, install a suction filter dryer.
Compressor
Windings Open
After the compressor has cooled, check the continuity of the compressor windings. If the windings are
open, replace the compressor.
Unit OFF on
high-pressure control
Discharge
Pressure Too High
In “COOLING” mode: Lack of or inadequate water flow. Entering water temperature is too warm.
Scaled or plugged condenser.
In “HEATING” mode: Lack of or inadequate air flow. Blower inoperative, clogged filter or restrictions in
d
uct wo
rk
Refrigerant Charge
The unit is low on refrigerant. Check for a refrigerant leak and repair, then evacuate and recharge with
the factory-recommended charge.
Low-Pressure
Switch
Check for a defective or improperly calibrated low-pressure switch.
Unit OFF on
low-pressure control
Suction Pressure
Too Low
In “COOLING” mode: Lack of/or inadequate air flow. Entering air temperature is too cold. Blower
inoper
ative, clogged filter or restrictions in duct work.
In “HEATING” mode: Lack of/or inadequate water flow. Entering water temperature is too cold. Scaled
or plug
ged condenser.
Refrigerant Charge
The unit is low on refrigerant. Check for a refrigerant leak and repair, then evacuate and recharge with
the factory-recommended charge.
Low-Pressure
Switch
Check for a defective or improperly calibrated low-pressure switch.
Unit short cycles
Unit Oversized Recalculate heating and or cooling loads.
Thermostat/
Controller (DDC)
Thermostat was installed near a supply air grill; relocate thermostat. Readjust heat anticipator.
Wiring and
Controls
Check for a defective or improperly calibrated low-pressure switch.
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EC Series Heat Pumps — 8733841499 (2024/05)