Bosch SM Series Installation, Operation And Maintenance Manual page 24

24 | Troubleshooting
Problem
UNIT SHORT
CYCLES
INSUFFICIENT
COOLING OR
HEATING
BLOWER
OPERATES
BUT
COMPRESSOR
DOES NOT
Table 11 Unit Troubleshooting
8733826256 (2020/06)
Unit Troubleshooting
Possible Cause
Unit Oversized
Thermostat
Wiring and Controls
Unit Undersized
Loss of Conditioned Air by
Leakage
Airflow
Refrigerant Charge
Compressor
Reversing Valve
Operating Pressures
TXV
Moisture, Non-condensables
Thermostat
Wiring
Safety Controls
Compressor
Overload Open
Compressor
Motor Grounded
Compressor
Windings Open
Subject to change without prior notice
Checks and Corrections
Recalculate heating and or cooling loads.
If the thermostat is installed near a supply air grill,
relocate thermostat. Adjust the heat anticipator.
Check for defective or improperly calibrated low-
pressure switch.
Recalculate heating and or cooling loads. If excessive,
possibly adding insulation and shading will rectify the
problem.
Check for leaks in duct work or introduction of ambient
air through doors or windows.
Lack of adequate airflow or improper distribution of air.
Replace dirty filter.
Refrigerant charge low causing inefficient operation.
Check for defective compressor. If discharge is too low
and suction pressure is too high, compressor is not
pumping properly. Replace compressor.
Defective reversing valve creating bypass of refrigerant
from discharge of suction side of compressor. Replace
reversing valve.
Compare unit operation pressures to the pressure/
temperature chart for the unit.
Check TXV for possible restriction or defect. Replace if
necessary.
The refrigerant system may be contaminated with
moisture or non-condensables. Reclaim refrigerant,
replace filter dryer, evacuate the refrigerant system, and
recharge with factory recommended charge.
Check setting, calibration, and wiring.
Check for loose or broken wires at compressor,
capacitor, or contactor.
Check UPM board red default L.E.D. for Blink Code
If the compressor is cool and the overload will not reset,
replace compressor.
Internal winding grounded to the compressor shell.
Replace the compressor. If the compressor is burnt out,
install a suction filter dryer.
After compressor has cooled, check continuity of the
compressor windings. If the windings are open, replace
the compressor.
SM Split AH/AV Air Handler
SM Split AH/AV Air Handler