Chilled-water troubleshooting

If leaving chilled water is on design and flow is real, hunt zones. If leaving water is warm, hunt plant: load vs capacity, condenser limits, machine alarms.

Symptoms: low ΔT, some risers starved, air noise, VFDs at odd speeds. Checks: differential pressure setpoint, bypass valves, strainers, coil actuators, primary-secondary decoupler behavior.

High head or high CW return: tower fans, fill, approach vs wet-bulb, air-cooled coil dirt, recirculation. A chiller cannot invent a colder condenser than physics allows that day.

Only after water sides make sense:

• low refrigerant charge / leaks,
• failed compressors or unloaders,
• oil issues,
• sensor errors lying to the controller,
• purge problems on low-pressure machines,
• absorption heat/solution faults.

Bring logs. Interview operators about recent tower work, valve projects, and control upgrades. Many failures start the day after “someone optimized” a setpoint.

Pull the one-line of the plant: which chiller serves which header, design CHW and CW temps, design gpm. Troubleshooting without the sheet is archaeology.

If two chillers fight — one loaded, one surging or short-cycling — look at sequencing setpoints, reverse return issues, and check valves. Staging logic errors look like mechanical failure.

New buildings often have strainers full of scrap and sensors left in protective caps. Week-one “capacity shortage” is frequently debris and controls commissioning debt.

Rupture disc events, oil dumps into evaporators, and absorption crystallization need seasoned techs and OEM support. Your layered approach still frames the call correctly for the specialist.

Once a year, compare critical temperature sensors to a reference. Chiller fights between units sometimes start because one leaving-water sensor reads 3°F low and steals all the load.

### Field memory hooks

Write the key temperatures, flows, or mode checks for this topic on your job notes. Teach the helper beside you to repeat the layered order aloud before tools come out. Most callbacks shrink when the first visit follows a written order instead of a parts guess.

When OEM data exists — capacity tables, wiring diagrams, water-flow charts — photograph the rating plate and the page you used. Future you (or the next tech) should not have to rediscover the same facts under pressure.

Situation. After a controls upgrade, chillers short-cycle and occupants complain of humidity. CHW setpoint was dropped aggressively while minimum flow bypass was disabled. Evaporator flow swings wildly.

What to think. Control strategy broke hydraulics and machine stability. Restore minimum flow and sensible setpoints; retune.

Conclusion. Troubleshooting includes controls politics, not only wrenches.

### Teach-back for the helper

Before leaving the topic, have the helper explain in their own words: what is normal, what is measured first, and what must never be skipped for safety. If they cannot teach it back, review the main “How it works” blocks again with a sketch on paper.

Connect this lesson to the previous one and the next one as a chain. Field skill is sequence memory — not isolated trivia. Keep OEM charts and job photos with the work order so the next visit starts smarter.

### Common measurement habits

Use the same meter locations every time so readings compare day to day. Steady the system before judging pressures or temperatures — mid-shift and mid-defrost lie. Write ambient conditions on every note page.

If a reading disagrees with the control display, believe the calibrated handheld until sensors are proven. Controls cannot fix what they cannot see accurately.