- Alarm AL175 is active for Circuit 1, showing Compressor Overload. This means the chiller has detected that the compressor's motor safety (overload relay) tripped and shut off the compressor.
- As a result, Circuit 1's compressor is not running. You might have noticed the compressor trying to start then cutting out, or it may not run at all now. The chiller may attempt to run other circuits (if available) or just stay off for that circuit.
- Often there's an indicator on the electrical panel for a tripped compressor overload. If you open the panel (qualified personnel only), the compressor contactor or overload relay might have a visible tripped indicator or button popped out. There may also be a slight burnt smell if the trip was due to electrical overheating.
High Electrical Current Draw
The compressor motor pulled more current than its limit, causing the overload protector to trip. This can happen due to high head pressure (compressor working too hard, e.g. if condenser is dirty or overcharged refrigerant) or a tight/internally damaged compressor struggling to turn.
Locked Rotor or Hard Start
If the compressor failed to start properly (locked rotor condition or a starting capacitor issue for single-phase), the sudden high amperage will trip the overload almost instantly.
Electrical Supply Issues
Phase imbalance, low voltage, or power spikes can lead to overheating of the motor and an overload trip. A motor starved of voltage runs hot and can trip on overload even under normal mechanical load.
Faulty Overload or Sensor
It's possible the overload relay itself is overly sensitive or malfunctioning. However, given its critical role, assume the trip was valid until proven otherwise.
Inspect Compressor Conditions
Before resetting anything, do a quick visual check. Is the condenser clean and fans working (to rule out high pressure cause)? Also listen for any unusual sounds from the compressor area. If everything looks normal externally, proceed to reset.
Reset the Compressor Overload
Turn off power to the chiller for safety. Open the electrical panel covering Circuit 1's compressor controls (only if you are trained/authorized). Locate the compressor's overload relay (often part of or near the contactor labeled Q1 for compressor 1) and press the reset button on it. It usually clicks back into place.
Check Electrical Connections
While in the panel, if you are comfortable, visually inspect the wiring to the compressor contactor – loose connections can cause heating. Tighten any obviously loose lugs (with power off, using appropriate tools).
Power On and Reset Alarm
Close up the panel and restore power. Reset the AL175 alarm on the controller (hold reset button ~5 seconds) to clear it. The chiller will attempt to restart the compressor.
Observe Startup and Running Amps
If you have a way to monitor the compressor amperage (some advanced chillers display current, or using a clamp meter if qualified), watch the compressor as it starts. It should ramp up and then settle at its normal running current. Listen for smooth operation.
Lighten the Load Temporarily
If possible, reduce the cooling load or raise the temperature setpoint slightly for initial restart. This makes it easier on the compressor until you're sure it's running reliably. You can return to normal setpoint after a short while.
Professional Help Required:
- If the compressor trips off again right away after resetting (you hear a click and it stops, or AL175 comes back), stop trying to reset it repeatedly. This indicates a persistent fault – possibly a seized compressor or a serious electrical problem.
- Even if you get it running, if AL175 has occurred multiple times in a short period (or becomes frequent), something is causing the compressor stress.
- If you measured voltage and found it out of spec, or suspect phase imbalance (for three-phase units), an electrician or HVAC tech should address this.
- Given that resetting a compressor overload involves opening the electrical cabinet, if you do not have the expertise, do not attempt it.
- Should the compressor be at fault (e.g., it's internally damaged or worn out), a technician will be needed to replace it and recharge the system.
A professional HVAC technician can perform tests like a megohmmeter check on the motor or investigate mechanical failure. They might perform tests to check for high head pressure, incorrect refrigerant charge, or motor wear issues. Always involve professionals for major interventions like compressor replacement.