JOHNSON CONTROLS
188
FORM 150.72-NM3 (1020)
ISSUE DATE 10/05/2020
SECTION 9 – SERVICE AND TROUBLESHOOTING
PROBLEM
CAUSE
SOLUTION
“MP / HPCO” FAULT
1. Compressor internal motor
1. Verify refrigerant charge is
protector (MP) open.
not low. Verify superheat
setting of °10 – 15 °F (5.6° –
8. 3 °C). Verify correct com-
pressor rotation. Verify
compressor is not over
loaded.
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
1. Demand not great enough.
1. No problem. Consult
START
“Installation” Manual to aid
in understanding compres-
sor operation and capacity
control.
2. Defective water temperature
2. Compare the display with a
sensor.
thermometer. Should be
/- 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.
1. Contact the local Johnson
Low suction pressure will
Controls service
be
observed.
representative.
2. Improper flow through the
2. Reduce flow to within chiller
evaporator.
design
specs.
See Limita-
tions in Installation section.
3. Low refrigerant charge.
3. Check subcooling and add
Low suction pressure will
charge as needed.
be observed.
TROUBLESHOOTING (CONT’D)
Summary of Contents for YLAA0285SE
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