Absorption Heat Pump Troubleshooting

Machine Status and Basic Operations

Q: What does “MACHINE NOT READY TO START” status mean?

A: This status appears when:

• The machine has not completed the ‘DILUTION’ cycle before power off
• There’s a critical trip condition (TOTAL SHUTDOWN)
• The machine is in compulsory dilution after certain alarms
• Field interlocks are not satisfied (pumps, flow switches, etc.)

Resolution Steps:

1. Check if dilution cycle needs to be completed (wait 20 minutes)
2. Verify all field interlocks are healthy
3. Reset any active alarms after addressing root cause
4. Ensure Heat Source Water and District Water pumps are running

Q: Why won’t my heat pump start?

A: Common reasons for startup failure:

• Heat Source Water Flow Switch not activated
• Heat Source Water DP Switch not activated
• Heat Source Water Pump feedback signal missing
• Machine in TRIP or DILUTION status
• Critical alarms present

Troubleshooting Steps:

1. Check Heat Source Water flow rate (should be 50-60% of rated minimum)
2. Verify Heat Source Water pump is running and feedback signal received
3. Check for any active alarms on operator panel
4. Ensure machine status shows “READY TO START”
5. Wait for startup sequence timeout (10 minutes) if flow issues persist

Q: What is the DILUTION cycle and why does it occur?

A: DILUTION is a 20-minute safety cycle that:

• Prevents LiBr crystallization in heat exchangers
• Equalizes concentration and temperature throughout the system
• Occurs automatically after certain trips or power failures
• Cannot be interrupted when marked as “COMPULSORY DILUTION”

When DILUTION occurs:

• After power failure (>3 minutes requires compulsory dilution)
• Generator temperature high trips
• Refrigerant pump trips
• Normal machine shutdown
• Various temperature sensor errors

TOTAL SHUTDOWN Alarms

Q: What should I do when I get “ANTIFREEZE TRIP” alarm?

A: This critical alarm occurs when Heat Source Water outlet temperature drops below freezing point.

Immediate Actions:

1. Machine automatically stops all pumps and closes steam valve
2. Heat Source Water pump continues running to prevent freezing
3. DO NOT restart until temperature rises above setpoint + hysteresis

Root Cause Investigation:

• Check Heat Source Water supply temperature
• Verify adequate flow rate through evaporator
• Inspect for blockages in Heat Source Water circuit
• Check if load demand is too low causing overcooling

Q: How do I handle “HEAT SOURCE WATER PUMP TRIP” alarm?

A: This alarm indicates the Heat Source Water pump is not responding or has tripped.

Troubleshooting Steps:

1. Check Heat Source Water pump motor starter
2. Verify electrical connections to pump
3. Ensure pump feedback contact is wired correctly
4. Check for mechanical issues with pump
5. Reset pump motor protection if tripped
6. Alarm can only be reset after pump run feedback is received

Q: What causes “HEAT SOURCE WATER FLOW SWITCH TRIP”?

A: Flow rate has dropped below 50-60% of rated value.

Resolution:

1. Check Heat Source Water pump operation
2. Inspect for blockages in piping
3. Verify flow switch setting (should be 50-60% of rated flow)
4. Check for closed valves in Heat Source Water circuit
5. Look for air locks in system
6. Ensure adequate water supply pressure

Q: “ABSORBENT PUMP TRIP” – what should I check?

A: The absorbent pump motor has drawn excessive current or AC drive has faulted.

Diagnostic Steps:

1. Check MPCB/Overload relay status – reset if tripped
2. Verify AC drive status and error codes
3. Check for mechanical binding in pump
4. Inspect electrical connections
5. Verify pump is not running dry
6. Check LiBr solution levels in system

DILUTION Alarms

Q: Why do I get “GENERATOR TEMPERATURE HIGH” alarm?

A: Generator temperature exceeded safe operating limit, risking LiBr crystallization.

Causes and Solutions:

• Excessive steam flow: Check steam control valve operation and setpoints
• Low District Water flow: Verify District Water pump and flow rates
• High District Water inlet temperature: Check cooling system
• Faulty temperature sensor: Calibrate or replace sensor
• PID control issues: Review controller parameters

Prevention: Monitor generator temperature trends and adjust steam flow accordingly

Q: What does “DISTRICT HOT WATER INLET TEMP LOW” mean?

A: District Water inlet temperature dropped below minimum setpoint, risking LiBr crystallization in absorber.

Resolution:

1. Check District Water supply temperature
2. Verify heating system upstream is functioning
3. During startup, this safety is bypassed for first 30 minutes
4. Adjust setpoint if consistently triggering during normal operation
5. Ensure adequate heat rejection capacity

Q: “REFRIGERANT PUMP TRIP” – how do I resolve this?

A: Refrigerant pump motor overcurrent or mechanical failure.

Troubleshooting:

1. Reset MPCB/Overload relay
2. Check refrigerant level in evaporator
3. Verify pump not cavitating (check suction pressure)
4. Inspect pump mechanical condition
5. Check electrical supply to pump
6. Ensure refrigerant level electrodes are functioning

Level Control Issues

Q: How do the level electrodes work?

A: Three sets of level electrodes monitor solution levels:

Absorber Level (AE1-AE4):

• AE1: 50% sight glass level
• AE2: 25% sight glass level
• AE3: 0% sight glass level (critical low)
• AE4: Reference electrode

Actions:

• Below AE2: Auto blowdown valve opens
• Below AE3: Steam valve closes completely
• Above AE1: Auto blowdown valve closes

Generator Level (GE1-GE3):

• GE1: Normal maximum level
• GE2: Restart level
• GE3: Reference electrode

Q: “Auto blowdown valve not working” – what to check?

A: Auto blowdown valve transfers refrigerant to absorber when level is low.

Troubleshooting:

1. Verify absorber level electrode signals
2. Check valve electrical connections
3. Ensure refrigerant pump is running (valve only opens when pump ON)
4. Inspect valve for mechanical binding
5. Verify valve solenoid coil integrity
6. Check PLC logic and I/O modules

Crystallization Prevention

Q: How does the system prevent LiBr crystallization?

A: Multiple protection methods:

Steam Control Valve Modulation:

• PLC calculates solution concentration and crystallization temperature
• Maintains safe temperature margin above crystallization point
• Overrides capacity control when crystallization risk detected

Absorber Level Control:

• Low level indicates possible crystallization in spray lines
• Auto blowdown dilutes solution when level drops

Temperature Monitoring:

• Multiple temperature sensors monitor critical points
• Automatic valve closure when safe limits exceeded

Q: What if I suspect crystallization has occurred?

A: Signs of crystallization:

• Rapidly dropping absorber level
• High generator temperature with low steam flow
• Poor heat transfer performance
• Frequent level-related trips

Recovery Actions:

1. Allow extended dilution cycle (may take several cycles)
2. Check all solution temperatures
3. Verify proper operation of all level electrodes
4. Monitor concentration calculations on HMI
5. Contact service technician if problem persists

Control System Issues

Q: Steam control valve not responding properly?

A: Control valve issues affect capacity and safety.

Diagnostics:

1. Check valve position feedback vs. command signal
2. Verify 4-20mA control signal integrity
3. Test valve manually from HMI (Service Menu)
4. Check PID controller parameters
5. Inspect valve actuator and positioner
6. Verify steam supply pressure and valve sizing

Control Modes:

• Slow opening (thermal shock prevention)
• District Water temperature PID control
• Generator temperature limiting
• Crystallization prevention override
• Absorber level control override

Q: PLC communication errors – how to diagnose?

A: Communication between PLC and components:

HMI Communication:

1. Check Ethernet cable connections
2. Verify IP address settings
3. Check for electromagnetic interference
4. Restart HMI if screen frozen
5. Verify PLC CPU status LEDs

I/O Module Issues:

1. Check module LED status indicators
2. Verify field wiring connections
3. Check 24VDC supply to modules
4. Replace suspect modules
5. Verify module configuration in PLC program

Sensor and Measurement Issues

Q: Temperature sensor error alarms?

A: Temperature sensor failures affect control and safety:

Critical Sensors (cause TOTAL SHUTDOWN):

• Heat Source Water Outlet Temperature
• Antifreeze Thermostat

Dilution-causing Sensors:

• District Hot Water Inlet/Outlet Temperature
• Generator Temperature
• U-tube Temperature
• Spray Solution Temperature

Warning-only Sensors:

• Heat Source Water Inlet Temperature
• Dilute Solution Temperature
• Generator Top/Bottom Temperature
• Heat Reclaimer Outlet Temperature

Troubleshooting:

1. Check sensor wiring and connections
2. Verify RTD continuity (typically 100Ω at 0°C)
3. Check for moisture in junction boxes
4. Verify proper sensor mounting
5. Replace faulty sensors with identical specifications

Q: Vacuum transmitter reading incorrectly?

A: Vacuum measurement affects purging operation:

Checks:

1. Verify 4-20mA signal at PLC input
2. Check transmitter calibration
3. Inspect sensing lines for blockages
4. Ensure proper electrical connections
5. Compare with manual vacuum gauge if available

Automatic Purging System

Q: “PURGE PUMP NOT DEVELOPING VACUUM” alarm?

A: Purge pump cannot achieve ultimate vacuum setpoint.

Troubleshooting:

1. Check purge pump motor operation
2. Inspect pump mechanical condition
3. Verify all manual valves are properly positioned
4. Check for air leaks in vacuum lines
5. Clean or replace pump oil if applicable
6. Verify ultimate vacuum setpoint (typically 2-5 mmHg)

Q: “TANK PURGING FREQUENCY HIGH” warning?

A: More than 2 automatic purges per day indicates possible air leakage.

Investigation:

1. Check machine shell for air leaks
2. Inspect all gaskets and seals
3. Verify proper torque on flanged connections
4. Check purge system valves for proper sealing
5. Monitor vacuum levels during operation
6. Consider leak detection testing

Q: Purging system stuck in manual mode?

A: System shifted to manual due to malfunction.

Resolution:

1. Address root cause that triggered manual mode
2. Verify purge pump develops ultimate vacuum
3. Test all solenoid valves manually
4. Check vacuum transmitter operation
5. Reset to AUTO mode only after confirming proper operation

Preventive Maintenance Reminders

Q: What are key maintenance items to prevent trips?

A: Regular maintenance prevents most alarm conditions:

Daily Checks:

• Verify all pumps running smoothly
• Monitor temperature and pressure readings
• Check for unusual noises or vibrations
• Verify adequate solution levels

Weekly Checks:

• Clean HMI screen and check for alarms
• Verify flow switch and pressure switch operation
• Check electrical connections for tightness
• Monitor purging frequency and effectiveness

Monthly Checks:

• Calibrate temperature sensors
• Test safety shutdown systems
• Verify control valve operation
• Check solution concentration
• Inspect electrical panels for dust/moisture

Annual Checks:

• Complete control system calibration
• Replace batteries in transmitters
• Comprehensive leak testing
• Update PLC/HMI software if needed
• Professional controls system inspection

Emergency Procedures

Q: What to do in case of power failure?

A: Power failure during operation triggers automatic protection:

Automatic Actions:

• Machine enters DILUTION on power restoration
• If power loss <3 minutes: dilution can be bypassed
• If power loss >3 minutes: compulsory dilution required

Manual Actions:

1. Do not attempt to restart immediately
2. Allow dilution cycle to complete
3. Check for any damage during power outage
4. Verify all systems normal before restart
5. Monitor closely during first few hours of operation

Q: Emergency shutdown procedure?

A: If immediate shutdown required:

Steps:

1. Press STOP button on HMI
2. If HMI unresponsive, use emergency stop button
3. Close steam supply valve manually if necessary
4. Ensure Heat Source Water pump continues running
5. Do not stop District Water pump immediately
6. Allow system to cool gradually
7. Log all actions taken and conditions observed

Advanced Diagnostics

Q: How to interpret trend data for troubleshooting?

A: Use data logging for pattern analysis:

Key Parameters to Monitor:

• Generator and District Water temperatures
• Steam valve position over time
• Pump runtime hours and trip frequency
• Concentration calculations
• Vacuum levels and purging patterns

Trending Analysis:

• Gradual temperature increases may indicate fouling
• Frequent valve adjustments suggest control issues
• Increasing purge frequency indicates air leakage
• Pump trip patterns may show mechanical wear

Q: System performance declining – what to check?

A: Performance degradation troubleshooting:

Heat Transfer Issues:

1. Check for fouling in heat exchangers
2. Verify proper solution concentration
3. Monitor approach temperatures
4. Check for air in solution circuits

Control System Issues:

1. Verify sensor calibration accuracy
2. Check PID control parameters
3. Monitor valve response times
4. Verify proper setpoint values

Mechanical Issues:

1. Check pump performance curves
2. Monitor vibration levels
3. Verify proper solution levels
4. Check for internal leakage

Frequently Asked Questions (FAQs)

Q: What causes “HEAT SOURCE WATER PUMP TRIP”?
A: Check pump motor starter, electrical connections, feedback signal, or mechanical issues. Reset motor protection after fixing.

Q: Why does “HEAT SOURCE WATER FLOW SWITCH TRIP” occur?
A: Flow below 50-60% rated value. Check pump, piping blockages, flow switch settings, or closed valves.

Q: How to fix “ABSORBENT PUMP TRIP”?
A: Check MPCB/overload relay, AC drive errors, mechanical binding, or LiBr levels. Reset after resolving issues.

Q: Why do I get “GENERATOR TEMPERATURE HIGH” alarm?
A: Caused by excessive steam, low District Water flow, high inlet temp, or sensor issues. Check valve, flow, and PID settings.

Q: What does “DISTRICT HOT WATER INLET TEMP LOW” mean?
A: Inlet temp too low risks crystallization. Check supply temp, heating system, or adjust setpoint. Bypassed for 30 min at startup.

Q: How to resolve “REFRIGERANT PUMP TRIP”?
A: Check MPCB/overload, refrigerant level, pump cavitation, or mechanical issues. Reset after fixing.

Q: How do level electrodes work?
A: Absorber electrodes (AE1-AE4) monitor levels: AE1 (50%), AE2 (25%), AE3 (0%). Below AE2 opens blowdown; below AE3 closes hot water/steam valve.

Q: Auto blowdown valve not working. What to check?
A: Verify electrode signals, valve connections, solenoid, or PLC logic. Ensure refrigerant pump is on.

Q: How does crystallization prevention work?
A: Modulates steam valve based on concentration, maintains safe temp margin, and uses blowdown for low absorber levels. Monitor sensors for limits.

Q: What if crystallization occurs?
A: Signs: low absorber level, high generator temp, poor performance. Run extended dilution, check temps and electrodes, or contact us.

Q: Steam control valve not responding. How to diagnose?
A: Check feedback vs. 4-20mA signal, test manually, verify PID, actuator, or steam pressure.

Q: PLC communication errors. How to fix?
A: Check Ethernet cables, IP settings, module LEDs, 24VDC supply, or replace faulty modules.

Q: Temperature sensor error alarms?
A: Critical sensors (Heat Source Water Outlet, Antifreeze) cause shutdown; others trigger dilution or warnings. Check wiring, RTD continuity, or replace sensors.

Q: Vacuum transmitter reading incorrectly?
A: Verify 4-20mA signal, calibration, sensing lines, or compare with manual gauge.

Q: Why “PURGE PUMP NOT DEVELOPING VACUUM” alarm?
A: Check pump motor, mechanical condition, valve positions, air leaks, or oil. Verify setpoint (2-5 mmHg).

Q: What does “TANK PURGING FREQUENCY HIGH” mean?
A: Over 2 purges/day suggests air leaks. Inspect shell, gaskets, valves, and monitor vacuum trends.

Q: Purging stuck in manual mode. How to fix?
A: Resolve trigger cause, verify pump vacuum, test solenoid valves, and reset to AUTO mode.

Q: Key maintenance to prevent trips?
A: Daily: check pumps, temps, alarms. Weekly: verify flow switches, connections. Monthly: calibrate sensors, test alarms. Annually: full calibration, leak tests.

Q: What to do during power failure?
A: Wait for dilution on power restoration. If <3 min, bypass possible; if >3 min, compulsory dilution. Check systems before restart.

Q: Emergency shutdown procedure?
A: Press STOP on HMI, use emergency stop if needed, close steam valve, keep pumps running, and allow gradual cooling.

Q: How to interpret trend data?
A: Monitor generator/District Water temps, valve position, pump trips, concentration, and vacuum. Gradual changes suggest fouling; frequent purges indicate leaks.

Q: System performance declining. What to check?
A: Check fouling, solution concentration, sensor calibration, PID settings, pump performance, or leaks. Use trend data for analysis.