2 Safe Service of Low-Pressure Chillers
Learn how to identify leaks, prepare and recover refrigerant, protect chiller components, and verify safe repairs on low-pressure chillers.
How low-pressure chillers behave
Low-pressure chillers, often centrifugal machines using refrigerants such as R-11 or R-123, operate below atmospheric pressure in parts of the refrigerant circuit. A leak in a below-atmospheric section can draw air and moisture into the system. Refrigerant may escape from sections operating above atmospheric pressure.
These different leak behaviors make careful diagnosis and controlled pressure changes important. Service must also protect against refrigerant exposure and water-side freezing. Follow the chiller manufacturer's instructions, applicable codes, and the refrigerant's safety data sheet.
Prepare for safe service
Before work, identify the refrigerant, review site emergency procedures, notify affected personnel, and confirm that required ventilation, alarms, and personal protective equipment are available. Use for electrical and mechanical energy sources, and verify isolation before opening equipment.
Refrigerant can displace oxygen. Do not enter a space where a release may have created a hazardous atmosphere unless following the site's trained emergency response and monitoring procedures. If an alarm sounds or a significant leak is suspected, leave the area, alert others, and follow the facility's evacuation plan. Do not attempt an unprotected rescue.
Use certified equipment and prevent intentional refrigerant release. Section 608 requirements apply to stationary refrigeration service. EPA specifies evacuation levels before appliances are opened, subject to defined exceptions.
Find leaks and control test pressure
A removes , such as air, from a low-pressure system. Unusually frequent or prolonged purge operation can signal air infiltration through a leak. Rising head pressure or recurring moisture can also point to a problem, but these clues do not locate the leak.
Inspect likely sites—including gaskets, fittings, shaft seals, and heat-exchanger tubes—with a suitable detector or another approved locating method. For a water-side tube leak, follow the manufacturer's procedure for isolating and inspecting the affected water box.
For a charged low-pressure system, controlled heating, such as circulated warm water or a built-in heating or pressurization device, is generally preferred to raise pressure during leak checks. Nitrogen may be used only when the applicable procedure allows it. Never exceed the pressure limit on the chiller nameplate or in its service manual; overpressure can damage rupture discs and other components.
Plan recovery and evacuation
Plan the work before opening the system. Determine whether the repair is major, whether the appliance or a component can be isolated, and whether a specific recovery exception applies. EPA's definition of a includes removal of certain heat-exchange or compressor components, or opening a sufficiently large flow area for more than minutes.
Connect approved recovery equipment using low-loss connections, and verify that both the equipment and recovery cylinder are appropriate for the refrigerant. Recover liquid first when possible to speed recovery, then recover the remaining vapor. Removing liquid alone is not complete recovery.
During evacuation, circulate or remove water from the chiller as directed by the manufacturer. Excessive cooling during evacuation can freeze water in the tubes and damage the heat exchanger. When applicable, EPA Type III guidance calls for heating oil to about before removal to reduce refrigerant release from the oil.
When an is required, EPA's table specifies for low-pressure appliances. After reaching the required level, wait a few minutes and check whether pressure rises. A rise can indicate remaining liquid refrigerant or refrigerant desorbing from oil. Apply the current regulatory requirements and equipment instructions for the particular repair; do not assume this is required in every service situation.
For certain non-major repairs where the appliance will not be evacuated to the atmosphere after service, EPA regulations provide an alternative procedure: bring a low-pressure appliance to before opening, under specified conditions. For covered low-pressure refrigerants, use heat to raise pressure as much as possible; nitrogen use is restricted by refrigerant boiling-point conditions. Confirm the exact rule and procedure before relying on this exception.
Verify the repair and restart
Repair the leak, then perform an appropriate leak check before recharging. A pressure-hold or vacuum-decay result can show that pressure changes, but it does not by itself identify the leak location; use a locating method when needed.
Re-evacuate and recharge according to the manufacturer's procedure. For centrifugal chillers, introduce refrigerant vapor before liquid where specified to reduce the risk of freezing water in the tubes, and charge through the designated charging valve. Confirm normal operation and document refrigerant recovered or added, along with any required leak-inspection or verification results.