TL;DR
A chilled water valve that does not respond is almost always a failed actuator or a loss of control signal from the BAS. Confirm the 0-10V or 4-20mA signal at the actuator before replacing any hardware.
What you might see
- discharge air temperature not responding to control signals
- supply air warmer than setpoint despite full cooling demand
- valve actuator not moving when BAS sends a position change
- chilled water valve stuck open or stuck closed
Likely causes
Actuator control signal loss from the BAS controller due to a wiring fault or failed output module
Actuator drive mechanism failed (stripped gear or seized motor inside the actuator body)
Valve stem seized from scale or corrosion, preventing physical movement even when the actuator tries to move
Air supply failure on a pneumatic actuator (for older installations with pneumatic control)
Required tools
- Multimeter or 4-20mA loop tester
- BAS graphics access
- Replacement actuator (correct torque and control signal type)
- Wrench set for manual valve stem operation
Safety first
- Chilled water piping is under system pressure. Do not attempt to remove or replace the valve body without first closing the isolation valves and draining the coil circuit.
- Always confirm BAS output signal mode (voltage or current) before connecting a meter to the actuator terminal. Incorrect meter configuration can damage the BAS output.
Procedure
- 1
Confirm the BAS is sending a control signal to the valve actuator. Use the BAS graphic to check the commanded position versus the reported position.[1]
- 2
Measure the control signal at the actuator terminals with a multimeter or a loop tester. For 0-10V actuators, a 0V signal is fully closed and 10V is fully open. For 4-20mA, 4mA is fully closed and 20mA is fully open.
Warning: Use a multimeter in the correct measurement mode (voltage or milliamps). An ammeter placed in parallel across the signal wires will short the BAS output and may damage the controller. - 3
If the signal is present but the actuator is not moving, the actuator is failed. Replace the actuator with the correct torque rating for the valve size.
- 4
If the signal is absent, trace the wiring from the BAS output back to the actuator. Check for a broken wire, loose terminal, or failed BAS output module.
- 5
With the actuator removed, manually operate the valve stem with a wrench. If the stem does not move, the valve is seized and must be rebuilt or replaced.
- 6
After the repair, stroke the valve through full travel from the BAS and verify the discharge air temperature responds to valve position changes.
Sources
Trane Trane Performance Climate Changer Air Handling Unit (AHU) general technical documentation, Trane
AHU chilled water valve and actuator troubleshooting, BAS control signal verification, general HVAC references (general)
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