FORM 150.72-NM1 (1020)
175
JOHNSON CONTROLS
9
TROUBLESHOOTING (CONT’D)
PROBLEM CAUSE SOLUTION
LOW LIQUID TEMP FAULT
1. Improperly adjusted leaving
chilled liquid temp. cutout (glycol
only).
1. Re-program the leaving chilled liquid temp.
cutout.
2. Micro panel setpoint/range
values improperly programmed.
2. Re-adjust setpoint/range.
3. Chilled liquid ow too low.
3. Increase chilled liquid ow. Refer to
Limitations in Installation section.
4. Defective LWT or RWT sensor
(assure the sensor is properly
installed in the bottom of the well
with a generous amount of heat)
conductive compound).
4. Compare sensor against a known good
Temperature sensing device. Refer to
Service section for temp./voltage table.
MP / HPCO FAULT
1. Compressor internal motor
protector (MP) open.
1. Verify refrigerant charge is not low. Verify
superheat setting of 10 °F to 15 °F (5.6 °C to
8.3 °C). Verify correct compressor rotation.
Verify compressor is not overloaded.
2. External overload tripped. 2. Determine cause and reset.
3. HPCO switch open. 3. See “High Press. Disch.” Fault.
4. Defective HPCO switch. 4. Replace HPCO switch.
5. Defective CR relay. 5. Replace relay.
COMPRESSOR(S) WON’T START
1. Demand not great enough. 1. No problem. Consult “Installation” Manual to
aid in understanding compressor operation
and capacity control.
2. Defective water temperature
sensor.
2. Compare the display with a thermometer.
Should be within +/- 2 degrees. Refer to
Service section for RWT/LWT temp./voltage
table.
3. Contactor/Overload failure. 3. Replace defective part.
4. Compressor failure. 4. Diagnose cause of failure and replace.
LACK OF COOLING EFFECT
1. Fouled evaporator surface.
Low suction pressure will be
observed.
1. Contact the local Johnson Controls service
representative.
2. Improper ow through the
evaporator.
2. Reduce ow to within chiller design specs.
See Limitations in Installation section.
3. Low refrigerant charge. Low
suction pressure will be
observed.
3. Check subcooling and add charge as
needed.
TABLE 27 (cont’d) – TROUBLESHOOTING
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