Troubleshooting - Bosch SM Series Installation, Operation And Maintenance Manual

SM Split AH/AV Air Handler

TROUBLESHOOTING

A possible fault may be one or a combination of causes and solutions. Check each cause and adopt
"process of elimination" and or verification of each before making any conclusion.
Problem
ENTIRE UNIT DOES
NOT RUN
UNIT OFF DUE TO
HIGH-PRESSURE
CONTROL
UNIT OFF TO
LOW-PRESSURE
CONTROL
SM Split AH/AV Air Handler
Unit Troubleshooting
Possible Cause
Power Supply Off
Blown Fuse/Tripped Breaker
Voltage Supply Low
Thermostat
Discharge Pressure is Too
High
Refrigerant Charge
High-Pressure Switch
Suction Pressure
Too Low
Refrigerant Charge
Low-Pressure Switch
Subject to change without prior notice
Checks and Corrections
Close disconnect, apply power
Replace fuse or rest circuit breaker. If using fuses,
ensure they are the correct size.
If voltage is below minimum voltage specified on unit
data plate, contact local power company.
Set the fan to "ON," the fan should run. Set thermostat
to "COOL" with the lowest temperature setting, the unit
should run in the cooling mode (reversing valve
energized). Set unit to "HEAT" with the highest
temperature setting, the unit should run in the heating
mode. If neither the blower or compressor run in all
three cases, the thermostat could
be miswired or faulty. To ensure miswired or faulty
thermostat verify that 24 volts is available on the
condensing section low-voltage terminal strip between
"R" and "C," "Y" and "C," and "O" and "C." If the blower
does not operate, verify that there is 24 volts between
terminals "G" and "C" in the air handler. Replace the
thermostat if defective.
If in "COOLING" mode: Lack of or inadequate water
flow. Entering water temperature is too warm. Scaled or
plugged condenser.
If in "HEATING" mode: Lack of or inadequate load side
fluid flow. Blower inoperative, clogged filter
or restrictions in duct work.
The unit is overcharged with refrigerant. Reclaim
refrigerant, evacuate and recharge with the factory
recommended charge.
Check for a defective or improperly calibrated high-
pressure switch.
If in "COOLING" mode: Lack of or inadequate airflow.
Entering air temperature is too cold. Blower inoperative,
clogged filter or restrictions in duct work.
If in "HEATING" mode: Lack of or inadequate water flow.
Entering water temperature is too cold. Scaled or
plugged condenser.
The unit is low on refrigerant. Check for refrigerant leak,
repair, evacuate and recharge with factory
recommended charge.
Check for defective or improperly calibrated low-
pressure switch.
Troubleshooting | 23
8733826256 (2020/06)