Thermistor Failure; Enabling And Disabling Compressors; Compressor Discharge Check Valve; Low Saturated Suction - Carrier AquaSnap 30MPA Series Controls, Start-Up, Operation, Service, And Troubleshooting

SYMPTOMS
Compressor Cycles
Off on Loss of Charge
Compressor Cycles Off on Out
of Range Condition
Compressor Shuts Down on
High-Pressure Control
Unit Operates Too Long
or Continuously
Unusual or Loud System
Noises
Compressor Loses Oil
Hot Liquid Line
Frosted Liquid Line
Frosted Suction Line
Freeze-Up
CHILLED FLUID PROOF-OF-FLOW SWITCH OPEN —
After the problem causing the loss of flow has been corrected,
reset is manual by resetting the alarm with the scrolling
marquee.
OPEN 24-V CONTROL CIRCUIT BREAKER(S) — De-
termine the cause of the failure and correct. Reset circuit break-
er(s). Restart is automatic after MBB start-up cycle is
complete.
COOLING LOAD SATISFIED — Unit shuts down when
cooling load has been satisfied. Unit restarts when required to
satisfy leaving fluid temperature set point.
THERMISTOR FAILURE — If a thermistor fails in either an
open or shorted condition, the unit will be shut down. Replace
EWT, or LWT as required. Unit restarts automatically, but must
be reset manually by resetting the alarm with the scrolling
marquee.
CAUTION
If unit stoppage occurs more than once as a result of any of
the safety devices listed, determine and correct cause
before attempting another restart.
Table 51 — Troubleshooting
CAUSE
Loss of charge control. Acting erratically.
Low refrigerant charge
Low suction temperature

Thermistor failure

System load was reduced faster than controller could
remove stages
Temperature controller deadband setting is too low
High-pressure control acting erratically
Noncondensables in system
Condenser scaled/dirty (30MPW)
Fans in remote condensing unit (30MPA only) not operating
System overcharged with refrigerant
Low refrigerant charge
Control contacts fused
Air in system
Partially plugged or plugged expansion valve or filter drier
Defective insulation
Service load
Damaged compressor
Piping vibration
Expansion valve hissing
Compressor noisy
Compressor not pumping
Leak in system
Mechanical damage (Failed seals or broken scrolls)
Oil trapped in line
Shortage of refrigerant due to leak
Restricted filter drier
Expansion valve admitting excess refrigerant (note: this is a
normal condition for brine applications)
Stuck TXV (thermostatic expansion valve)
Improper charging
System not drained for winter shutdown
Loose thermistor
Repair leak and recharge.
Replace control.
Add refrigerant.
Raise cooler leaving fluid temperature set point.
Replace thermistor.
Unit will restart after fluid temperature rises back into the
control band. Avoid rapidly removing system load or
increase loop volume.
Raise deadband setting.
Replace control.
Purge system.
Clean condenser.
Repair or replace if defective.
Reduce charge.
Add refrigerant.
Replace control.
Purge system.
Clean or replace as needed.
Replace or repair as needed.
Keep doors and windows closed.
Check compressor and replace if necessary.
Support piping as required.
Check for loose pipe connections or damaged compressor
Check refrigerant charge.
Check for plugged liquid line filter drier.
Replace compressor (worn bearings).
Check for loose compressor holddown bolts.
Operation outside of compressor operating envelope. Con-
sider head pressure control, clean condenser. Check water
flow (cooler and condenser).
Advanced scroll temperature protection is active. Determine
high discharge temperature reason.
Repair leak.
Replace compressor.
Check piping for oil traps.
Repair leak and recharge.
Replace filter drier.
Replace valve if defective.
Replace valve if defective.
Make sure a full quantity of fluid is flowing through the cooler
while charging, and suction pressure in cooler is equal to or
greater than pressure corresponding to 32 F (0° C).
Recommended that system be filled with an appropriate gly-
col mixture to prevent freezing of pumps and fluid tubing.
Verify thermistors are fully inserted in wells.
ENABLING AND DISABLING COMPRESSORS —
Compressors in the 30MP units can be enabled or disabled in
the controls. To enable or disable a compressor, toggle the
value in the Configuration
compressor.
COMPRESSOR DISCHARGE CHECK VALVE — A
disk-type check valve in the discharge of the compressor pre-
vents high pressure discharge gas from flowing rapidly back
through the compressor at shutdown. This same check valve
prevents a high to low side bypass in multiple compressor
circuits.
LOW SATURATED SUCTION — Several conditions can
lead to low saturated suction alarms and the chiller controls
have several override modes built in which will attempt to keep
the chiller from shutting down. Low fluid flow, low refrigerant
charge and plugged filter driers are the main causes for this
condition. To avoid permanent damage and potential freezing
of the system, do NOT repeatedly reset these alert and/or alarm
conditions without identifying and correcting the cause(s).
COMPRESSOR SAFETIES — The 30MP units with Com-
fortLink controls include a compressor protection board that
protects the operation of each of the compressors. Each board
senses the presence or absence of current to each compressor.
53
REMEDY

SERV menu for each individual