Maintenance & Reliability · SOP

Chiller System Coolant Level & Pressure Verification

A systematic procedure for industrial technicians to measure, log, and interpret chiller system pressures, temperatures, and coolant levels to ensure peak efficiency and prevent mechanical failure.

Estimated Time

45 min

Difficulty

Advanced

Regulation

CSA B52 / ASHRAE 15

Version

1.0

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Purpose

To establish a uniform procedure for verifying the coolant level and operating pressures (suction and discharge) of a closed-loop chiller system. Ensuring correct coolant volume and pressure differentials is critical for preventing cavitation, compressor overheating, evaporator freeze-ups, and overall system inefficiency. This SOP directly supports the reliability engineering goal of maintaining optimal compressor lubrication and heat transfer coefficients.

Scope

This procedure applies to all water-cooled and air-cooled chillers utilizing a refrigerant-to-water or refrigerant-to-glycol heat exchanger. It covers the initial machine walk-down, sight glass verification, pressure gauge validation, and data logging requirements. This SOP is intended for certified refrigeration mechanics and industrial maintenance technicians performing daily, weekly, or monthly PM tasks.

Safety Precautions

LOTOLockout/Tagout (LOTO) must be performed on the chiller’s main electrical disconnect before any mechanical work. Verify zero energy state using a rated voltmeter.
PPEWear ANSI Z87.1 rated safety glasses, class 0 rubber insulating gloves with leather protectors, and steel-toed boots. Use cut-resistant gloves when handling metal components.
REFRIGERANTAvoid skin or eye contact with refrigerant. Ensure adequate ventilation to prevent asphyxiation. Keep a halide leak detector or electronic sniffer calibrated and available at all times.
PRESSURERelieve trapped pressure before removing any caps or plugs. Use proper service gauges and follow safe refrigeration practices. Never braze or weld on a pressurized line.

Required Tools & Materials

Calibrated refrigerant manifold gauge set with low-loss hoses
Digital thermometer with K-type thermocouple probe
Class I, Div 2 rated flashlight (or appropriate hazardous location rating)
Proper refrigerant type (R-134a, R-410A, R-123, etc.) and recovery cylinder
Personal Protective Equipment (PPE) as outlined in the safety section
SOP Log Sheet / CMMS tablet (e.g., ServiceGrid)
Approved glycol refractometer (if ethylene or propylene glycol is used)

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Procedure: Step-by-Step

1 Obtain a valid permit to work (PTW) if required. Perform Lockout/Tagout (LOTO) on the chiller's electrical disconnect at the Motor Control Center (MCC). Verify zero energy state with a rated voltmeter. Isolate the cooling water supply and return valves.

2 Locate the refrigerant sight glass on the chiller barrel or receiver. Verify a solid liquid column is present (no flash gas bubbles). Record the moisture indicator color (green = dry, yellow = wet).

3 Install the refrigerant manifold gauge set: low-side hose (blue) to the suction service valve, high-side hose (red) to the discharge service valve. Purge hoses. Record the suction pressure (psig). Calculate the Saturated Suction Temperature (SST) using a P-T chart for the specific refrigerant.

4 Record the discharge pressure (psig). Calculate the Saturated Condensing Temperature (SCT). Investigate high discharge pressure causes such as non-condensables, a fouled condenser, or a stuck fan cycling switch.

5 Measure the liquid line temperature at the outlet of the condenser or receiver using the thermometer. Calculate subcooling (SCT - Liquid Line Temp). Target subcooling is typically 8-15°F, verify against OEM literature.

6 Measure the suction line temperature 6 inches from the compressor. Calculate superheat (Suction Line Temp - SST). Target superheat is typically 8-12°F for DX systems. Low superheat risks liquid slugging; high superheat risks compressor overheating.

7 Measure the Entering and Leaving Water Temperatures (EWT and LWT) at the evaporator bundle. Calculate the Delta T. A lower-than-expected Delta T indicates a flow issue (fouled tubes, closed valve, air in system). A higher-than-expected Delta T indicates low flow.

8 Using the refractometer, draw a sample from the evaporator glycol loop. Record the freeze point. Verify the glycol concentration meets the lowest ambient temperature design requirement plus a 10°F safety factor.

9 Record all pressures, temperatures, superheat, subcooling, Delta T, and glycol concentration on the PM log sheet or directly into ServiceGrid. Return all valves to their normal operating positions. Set the chiller back to auto mode.

10 Verify the chiller starts and runs smoothly. Monitor compressor amps against the manufacturer's performance curve. Check for abnormal vibration, noise, or refrigerant leaks. Confirm normal operation before leaving the equipment room.

Chiller System Coolant Level & Pressure Verification

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