Symptoms

•    Main contactor or secondary (speed) contactor audibly chatters, buzzes or rapidly pulls in and drops out
•    Cooler starts and stops repeatedly
•    Intermittent operation in Auto or Manual mode
•    Issue may be worse during pump, drain valve, or speed change operation

Affected Products

•    Braemar RPB / RPA 3‑phase evaporative coolers
•    AL‑Series evaporative coolers (3‑phase)
•    Any Seeley evaporative cooler using:

• 3‑phase motor starter
• Control electronics enclosure
• External drain valve / solenoid
• Overload relays

Root Cause Overview (Short Answer)

Relay or contactor chatter is almost always caused by unstable control voltage, not a faulty contactor.

In Seeley evaporative coolers, the most common causes are: •    Voltage drop in the control circuit
•    Unstable output from the electronics enclosure
•    Intermittent overload auxiliary contacts
•    Poor neutral / control reference integrity

Replacing the contactor alone rarely fixes the issue unless the root cause is corrected.

Most Likely Causes (Ranked by Probability)

1. Undervoltage at the Contactor Coil (Most Common)

If the coil voltage drops below its holding threshold, the magnetic field collapses and re‑energises repeatedly → chatter.

Common causes in Seeley coolers:

•    Loose terminals in:

• Control wiring
• DIN rail terminals
• Wall controller wiring
• Electronics enclosure terminals
• Voltage drop through:
•           Long control cable runs
•           Worn or corroded isolator auxiliary contacts
•           Aged wall switch contacts
• Incorrect coil supply:
• 240 V coil supplied via reduced or phase‑derived voltage

✅ Check

Measure voltage directly across the contactor coil while it is chattering.
If voltage dips below ~85% of rated coil voltage, chatter will occur.

2. Control Supply Instability from Electronics Enclosure

RPB, RPA and AL coolers rely heavily on the electronics enclosure to supply and switch control signals.

Possible issues:

•    Internal control power supply brown‑out or cycling
•    Shared supply overloaded by:

• Drain valve
• Solenoids
• Additional accessories
  • Faulty relay / triac output oscillating
  •    Moisture ingress inside electronics enclosure (very common)

✅ Check • Does chatter begin when drain valve or pump activates?
• Does it stop when electronics enclosure is isolated and unit is run manually?
•    Measure control supply voltage under load

3. Overload Relay Auxiliary Contact Opening Intermittently

Each motor contactor includes an overload relay with a normally‑closed auxiliary contact in the control circuit.

If this contact opens intermittently, it creates a make–break–make loop that sounds exactly like contactor chatter.

Possible causes:

•    Overload current setting too low
• Missing or imbalanced phase causing thermal cycling
•    High‑resistance or damaged overload auxiliary contact

✅ Check • Measure current on all three phases
• Inspect overload auxiliary terminals for heat or looseness
• (For testing only) temporarily bypass overload auxiliary contact

⚠️ Do not leave overload bypassed after testing

4. Floating or Poor Control Neutral / Reference

If the control circuit neutral or common reference is: •    Loose
• Incorrectly shared between phases
•    Poorly bonded to earth

The control voltage may fluctuate, especially during motor starting or switching.

✅ Check • Neutral continuity from supply → electronics → contactor coil
• Earth connection integrity at earth point
•    No accidental phase‑to‑phase feeding of control circuit

5. Electrical Noise / Back EMF (Solenoids & Motor)

AL‑Series and RPB / RPA coolers include: •    Motor contactors
• Drain valve solenoids
•    Sensor wiring

Without suppression: •    Solenoid back‑EMF can induce voltage spikes
•    Motor switching noise can upset electronics

✅ Mitigation • Fit RC snubber or MOV across contactor coil
• Fit diode across DC solenoids (if DC)
•    Route sensor/control wiring away from motor cables

6. Mechanical Contactor Fault (Less Common)

Mechanical failure is rare compared to electrical causes, but possible.

Possible faults:

•    Weak or partially failed coil
• Damaged shaded pole ring (AC contactor)
•    Excessive vibration of panel or mounting

✅ Check • Swap with known‑good contactor
•    Check coil resistance vs manufacturer specification

7. Upstream Phase Loss or Supply Dip

If the incoming 3‑phase supply is unstable: •    Control transformer output (if fitted) may dip
• Motor inrush may pull voltage down
•    Contactor may drop out during starting

✅ Check • Phase‑to‑phase voltages at isolator during start
•    Upstream breakers, contactors or terminals for overheating

Recommended Diagnostic Sequence

Follow this order to avoid unnecessary part replacement:

1. Measure contactor coil voltage during chatter
2. Tighten all control terminals, especially DIN rail terminals
3. Check overload relay auxiliary contact continuity
4. Isolate electronics enclosure and test in Manual mode
5. Verify control neutral and earth integrity
6. Add coil suppression if not already fitted

Key Takeaway

Contactor or relay chatter in RPB, RPA and AL‑series evaporative coolers is almost always caused by unstable control voltage—most commonly poor connections, overload auxiliary contacts, or electronics supply instability—not a faulty contactor.