Marley A28MA-1 Cooling Tower Control System User Manual

Marley A28MA-1 Cooling Tower Control System Manual

Introduction

The Marley A28MA-1 Cooling Tower Control System is a two-stage temperature control designed for cooling towers and evaporative condensers. It uses a temperature-sensing bulb and capillary assembly to monitor water or air temperature and switch connected control circuits as conditions change. This arrangement helps maintain a selected operating temperature while supporting staged fan or equipment control.

The controller is suited to commercial, industrial, and mechanical-room applications where dependable outdoor temperature control is required. Its weather-resistant enclosure, dual switching contacts, and adjustable temperature range make it useful for cooling tower fans, condenser systems, pumps, and other staged equipment. The two-stage design can help reduce unnecessary cycling by allowing equipment to respond progressively to changing thermal loads.

Facility engineers, HVAC technicians, maintenance teams, and system integrators can use the Marley A28MA-1 in new installations or as a replacement control for compatible tower equipment. Typical applications include industrial process cooling, building HVAC condenser loops, refrigeration systems, and evaporative cooling equipment.

Before installation, verify the model, electrical requirements, connected load, wiring diagram, and equipment compatibility. The Marley A28MA-1 Cooling Tower Control System is a line-voltage control device, so installation and servicing should be performed by qualified personnel following applicable electrical and safety regulations.

Technical Specifications

• Control type: Two-stage temperature control using two SPDT snap-acting switches.
• Model: A28MA-1.
• Temperature range: 40°F to 120°F, or approximately 4.4°C to 48.9°C.
• Fixed differential: 5°F, approximately 2.8°C, at each switch.
• Between-stage differential: 8°F, approximately 4.4°C.
• Sensing element: Neoprene-coated bulb measuring approximately 3/8 by 4 inches with a 6-foot capillary.
• Maximum bulb temperature: 210°F, or approximately 99°C, during infrequent overrun conditions.
• Adjustment: Internal screwdriver slot and dial.
• Electrical connections: Screw-type terminals.
• Enclosure: Gasketed, rainproof Type 3R enclosure.
• Enclosure material: 0.062-inch cold-drawn steel with outdoor black enamel finish.
• Conduit connection: Welded 3/4-inch female connector.
• Approximate shipping weight: 2.3 pounds, or 1.0 kilogram.
• Electrical capacity: Ratings depend on voltage, load type, and wiring configuration. Confirm the product nameplate and approved documentation before connecting equipment.

Detailed Description and Everyday Operation

The Marley A28MA-1 Cooling Tower Control System senses temperature through a remote bulb connected to the control enclosure by a capillary tube. As the sensed temperature changes, the internal switches operate at their configured stages. These contacts can be connected to compatible starters, relays, fan motors, or other control equipment.

The first stage responds to the selected temperature setting. A second stage provides additional control as the temperature continues to change, making the unit suitable for staged cooling arrangements. The fixed differentials help limit rapid switching, although the complete system response also depends on motor starters, contactors, fan configuration, and tower load.

For reliable operation, mount the sensing bulb where it represents the temperature being controlled and protect the capillary from sharp bends, abrasion, vibration, and excessive heat. During routine care, inspect the enclosure gasket, conduit entry, terminals, capillary, and bulb for damage or corrosion. Keep the enclosure closed and clean the exterior with a dry or lightly damp cloth. Do not spray water or cleaning chemicals into the control.

Cooling tower maintenance should also include inspection of fans, basins, distribution components, water treatment, electrical starters, and safety devices. The controller should not be used as a substitute for required overload, disconnect, grounding, or lockout procedures.

Setup Guide for the Marley A28MA-1

1. Confirm that the controller model, electrical supply, connected equipment, and control sequence are compatible.
2. Disconnect power at the appropriate disconnecting means and apply lockout/tagout procedures before opening the enclosure.
3. Choose a location that is accessible for adjustment but protected from mechanical impact, flooding, excessive vibration, and temperatures outside the permitted operating environment.
4. Install suitable conduit and route conductors through the provided conduit connection. Use wiring practices required by local electrical codes.
5. Mount the temperature bulb at the approved sensing location. Avoid placing it against a hot surface, directly in a high-velocity stream, or where it can be damaged during tower service.
6. Connect the line and load conductors to the correct screw terminals according to the equipment wiring diagram. Tighten terminals securely without damaging the conductors.
7. Set the temperature dial to the required operating point. Make small adjustments and allow the system to stabilize before changing the setting again.
8. Restore power and test each stage independently. Confirm that the correct fan, starter, relay, or control circuit responds at the intended temperature.
9. Check that conduit fittings, the enclosure cover, and gasket are properly sealed before placing the system into normal service.

If a stage does not operate, first verify power, terminal connections, the control sequence, and the connected starter or relay. Never bypass protective devices to force operation.

Troubleshooting the A28MA-1 Temperature Controller

Controller does not respond

Verify the disconnect, fuses, circuit breaker, control voltage, and terminal connections. Confirm that the sensed temperature has reached the switching point and that the connected equipment is enabled.

Only one stage operates

Check the second-stage wiring, relay or starter, and the between-stage temperature difference. Confirm that the temperature has moved far enough beyond the first switching point to activate the second circuit.

Equipment cycles too frequently

Inspect the bulb location, verify that it is not exposed to an unstable temperature source, and check whether the connected equipment is oversized or responding too quickly. Review the system control sequence before changing the adjustment.

Temperature is inaccurate

Inspect the bulb and capillary for kinks, crushing, abrasion, or loose mounting. Compare the controller response with a calibrated thermometer at the same sensing location. Replace damaged sensing components rather than attempting field repairs.

Moisture or corrosion is visible

De-energize the circuit and inspect the cover gasket, conduit entry, and enclosure for water intrusion. Correct the source before returning the controller to service.

The A28MA-1 documentation identifies operating specifications rather than universal fault-code displays; therefore, no electronic error-code list should be assumed for this mechanical switching control. For persistent faults, record the model, wiring arrangement, supply voltage, measured temperature, and observed switch behavior. Contact the equipment manufacturer, authorized distributor, or a qualified HVAC controls technician for model-specific assistance and warranty guidance.

Pros and Cons

Advantages

• Two-stage control: Supports staged response for cooling tower fans or related equipment.
• Broad adjustment range: The 40°F to 120°F range covers many cooling and evaporative condenser applications.
• Outdoor-ready enclosure: The gasketed Type 3R design is intended for rain-exposed installations when correctly mounted and sealed.
• Simple service approach: Screw terminals, a mechanical dial, and a remote bulb make the controller straightforward to inspect and configure.
• Useful replacement format: The compact control can suit systems that do not require a programmable controller or networked building automation interface.

Limitations

• Limited digital functionality: It does not provide a display, remote monitoring, data logging, or app-based control.
• Mechanical adjustment: Precise temperature management may be less flexible than a modern electronic sensor and programmable controller.
• Installation-specific wiring: Motor, relay, and starter connections must be selected for the actual voltage and load.
• Qualified service required: Line-voltage wiring and cooling tower equipment create electrical, mechanical, and water-treatment hazards.
• Best suited for: Conventional two-stage cooling tower or evaporative condenser systems. Systems needing network integration, advanced alarms, variable-speed optimization, or detailed temperature records may require a different control platform.