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Kohler Decision-Maker MPAC 1200 Transfer Switch Controller — Operation & Service Guide

Microprocessor controller for Kohler automatic transfer switches that moves the coach or facility load between utility (shore) and generator power. This guide covers the display and LEDs, test and exercise functions, fault meanings and resets, and the factory service schedule.

Overview

The Decision-Maker MPAC 1200 is the brains of a Kohler automatic transfer switch (ATS). It watches two power sources — Source N (normal, usually utility/shore) and Source E (emergency, usually the generator) — and moves the load contactor between them. When the preferred source fails, the controller signals the generator to start, waits for acceptable voltage and frequency, transfers the load, then retransfers and shuts the generator down (after a cooldown) when the preferred source returns. It supports standard-transition, programmed-transition (pause in OFF), and closed-transition (sub-100 ms overlap when sources are synchronized) switch mechanisms, plus a built-in exerciser, event history (last 100 events), Modbus/USB/optional Ethernet communications, and optional I/O, alarm, and external-battery modules.

How it works

The user interface has a four-line LCD, four soft-key pushbuttons whose functions appear on the bottom display line, and six LEDs: Source N Available (green), Source E Available (red), Position A/Normal (green), Position B/Emergency (red), System Alert (red — flashes on a fault), and Not in Auto (red — the ATS is not set for automatic operation or a load-shed sequence is active; it flashes while waiting for a manual transfer). From the main menu, View shows status, voltages, frequency, current, time delays, event history and maintenance records; Set enters setup; Test starts a test sequence. Setup and Test are password protected — four digits, factory default 0000. A lamp test (down arrow from the main menu, then Lamp Test) lights all six LEDs and the LCD.

Test choices: an unloaded test starts and runs the generator without transfer; a loaded test simulates a preferred-source failure and transfers the load with all time delays; an auto-loaded test transfers, runs for a set time (default 30 minutes, adjustable 1–60), and transfers back automatically; closed-transition models add a sync check that displays the phase-angle difference between sources without transferring. If the standby source fails during a loaded test, the ATS immediately retransfers to the preferred source.

Routine maintenance

The controller itself is maintenance-free electronics; scheduled maintenance is about proving the transfer system works and keeping the switch clean, tight, and cool. Kohler designates most internal work for an authorized distributor/dealer; the operator items are the exercise, the monthly test, and external inspections.

Weekly — generator exercise

Program the exerciser (Set > Exerciser) to start and run the generator under load once a week. Unloaded exercise runs the set without transfer (and can drive a load bank output); loaded exercise transfers the coach load to the generator. The next scheduled run shows on the main screen (e.g., "LD Exer 12/14 @ 16:00"). An exercise is skipped if a test or peak-shave is active, and a real source failure during exercise cancels it and resumes normal operation.

Monthly — automatic operation test

  1. Verify Position N and Source N Available LEDs are lit and the generator master switch is in AUTO.
  2. Press Test, enter the test password, step to Type of Test: Loaded, press Start.
  3. Verify the generator starts, Source E Available lights, time delays run, and the switch transfers (Position N out, Position E on).
  4. Press End Test; verify retransfer to Source N and that the engine-start signal drops after the cooldown delay so the generator stops.
  5. While testing, also inspect the outside of the switch for vibration, leakage, heat, or contamination, and check external hardware tightness.

Every 2 months (if SPD equipped)

Check surge-protective-device status indicators and the condition of the SPD connecting leads.

Annually — dealer service

Have an authorized distributor/dealer inspect for overheating signs (discolored metal, melted plastic, burning odor), clean and relubricate the contactor's external operating mechanism, tighten control and power wiring to specification, inspect wiring insulation, evaluate the main power switching contacts (clean/replace per the service manual), test all LEDs and remote controls, and inspect internal condition. Clean with a vacuum or dry cloth only — never compressed air, which lodges debris in the mechanism.

Operating tips

  • Change the default 0000 passwords so only authorized people can start tests — a loaded test starts the generator and moves the load. The test password can be reset or disabled from Setup > Reset Data (disable it only in secured locations).
  • The display returns to the main menu after 10 minutes idle; source voltages on the main screen are live measurements and a quick health check.
  • Use View > Event History (last 100 events) when diagnosing nuisance transfers; reset maintenance records after servicing so "since last maintenance" counters are meaningful.
  • After connecting or replacing accessory modules, expect a Module Status Change fault — reset it per the module procedure rather than ignoring it.
  • On closed-transition units, if sources will not synchronize the programmed-transition override takes over (automatic) or waits for the operator (manual, setup password required).

Safety

  • Hazardous voltage will cause severe injury or death. Both sources feed the enclosure; disconnect all power sources before opening it. Only authorized personnel should open the enclosure.
  • Before any service, disable the generator: master switch OFF, battery charger unplugged, battery cables removed (negative first) — the ATS engine-start contacts or a remote command can start the set at any time.
  • Test circuits with a voltmeter to verify de-energized, remove jewelry, and stand on an insulated mat before touching anything inside.
  • Wear a grounding wrist strap when handling the controller's circuit boards — ESD destroys them.
  • Replace all barriers and close and lock the enclosure door before reapplying power.

Maintenance schedule

TaskIntervalPartsNotes
Exercise the generator set under load via the exerciser as needed — Weekly (operator task). Program in Set > Exerciser; loaded exercise transfers the load, unloaded runs the set only.
Test the automatic control system (loaded transfer test) 1 months — Operator task. Verify full sequence: generator start, time delays, transfer to Source E, retransfer to Source N, engine cooldown and stop. Observe all LEDs during the test.
External inspection — vibration, leakage, excessive temperature, contamination, deterioration 1 months — Kohler recommends a weekly general external look-over as well; monthly formal check. Clean with vacuum/dry cloth only — never compressed air. More often in dusty areas.
Check external hardware in place, tightened, not badly worn 1 months — Operator task; replace worn/missing components with manufacturer-recommended parts.
Inspect SPD status indicators and connecting leads (if surge protection fitted) 2 months — Every two months on switches with optional SPD modules.
Internal inspection — dirt, corrosion, loose hardware, insulation damage, overheating signs 1 months — De-energize all sources first. Contact an authorized distributor/dealer if any contamination, corrosion, discoloration, melted plastic, or burning odor is found.
Check for overheating or loose connections (discolored metal, melted plastic, burning odor) 12 months — Annual; repair by authorized distributor/dealer.
Clean and relubricate contactor external operating mechanism 12 months — Annual; cleaning/lube by authorized distributor/dealer. More often in dusty service.
Tighten control and power wiring connections to specification 12 months — Annual; authorized distributor/dealer.
Inspect main power switching contacts; clean or replace contacts/contactor assembly as needed 12 months — Annual; service-manual task for authorized distributor/dealer.
Test all LED indicators and remote control systems 12 months — Annual. Operator can run the lamp test any time: Main menu > down arrow > Lamp Test (all 6 LEDs + LCD).
Reset maintenance records after service 12 months — Setup > Reset Data > Reset Maintenance Records updates last-maintenance date and since-reset counters.

Troubleshooting

System Alert LED flashing with a fault message on the display
  1. Read the fault text on the main screen — it names the condition
  2. Identify and correct the cause, then from the Main menu press the down arrow to the Reset menu and press Reset
  3. A fault reset does not change controller settings
  4. Warnings (vs. faults) clear automatically on a source-availability change or transfer request
Fail to Acquire Standby (or Preferred) Source — generator did not come up
  1. Source voltage never reached the acceptable window within the set time delay
  2. Verify the generator master switch is in AUTO and the set starts locally
  3. Check generator battery, fuel, and fault codes at the set
  4. Review pickup/dropout voltage-frequency settings and the acquire time delay in Setup
Fail to Transfer warning — switch signaled but position did not change
  1. The main-shaft auxiliary switch did not confirm a complete position change; the controller retries three times before flagging
  2. Check the contactor mechanism for binding or obstruction (de-energized!)
  3. Have the dealer inspect the operating mechanism and auxiliary switches
Aux Switch Fault or Aux Switch Open (manual-reset fault; ATS operation halted)
  1. Aux Switch Fault: auxiliary switches report more than one position at once, or the position changed with no transfer signal
  2. Aux Switch Open: auxiliary switches report the ATS in neither position (all inputs open)
  3. De-energize and inspect the main-shaft auxiliary switch wiring and actuation
  4. Correct the cause, then reset from the Reset menu; these faults stop active modes and let the generator cool down and stop
Module Status Change / Module Status Conflict message
  1. Status Change appears when an accessory module is connected or disconnected: press Reset, then Reset New Module for new hardware, or run the Module Uninstall procedure (Set > Inputs/Outputs > Set Auxiliary I/O > Status: Lost > Uninstall Module Yes > Save) for removed hardware
  2. Status Conflict means a different module type now uses the same address: power down, disconnect the module, clear the fault, uninstall the old module, then power down again, connect the new module and reset
  3. A Status Change that will not clear can indicate a failed real-time clock — the logic board may need replacement (dealer)
Src N / Src E Rotation Err (three-phase systems)
  1. Detected phase rotation of a source does not match the preselected setting — self-resetting once corrected
  2. Verify source wiring rotation, or correct the phase-rotation setting in Setup > Set Sources
I/O Module Lost Comm
  1. An I/O device stopped communicating or has a wrong address
  2. Check module cable connections and address; the fault self-resets when communication is restored
Not in Auto LED lit or flashing
  1. ATS is not set for automatic operation, or a load-shed (forced transfer to OFF) sequence is active
  2. Flashing = waiting for a manual (supervised) transfer — set the supervised transfer control switch to Auto
  3. Check for active Inhibit Transfer or Forced Transfer to OFF programmable inputs
Scheduled exercise never runs
  1. Check the main screen's second line for the next scheduled run — blank means no exercise is programmed
  2. Verify the exercise event is enabled in Set > Exerciser (events can be temporarily disabled)
  3. Exercises are skipped while a system test or peak-shave is active
  4. Verify controller time/date (and DST setting) are correct
Password not accepted / unknown password
  1. Passwords are 4 digits; factory default is 0000; entry times out after 30 seconds
  2. Use the open up-arrow to set each digit and the open right-arrow to move digits, then OK
  3. The test password can be reset to default or disabled from Setup > Reset Data (setup password required)
External Battery Low warning
  1. The battery on the External Battery Supply Module (EBSM) is low
  2. Test/replace the external battery and verify its charging supply

Based on: Kohler Operation Manual TP-6866 (6/21), Decision-Maker MPAC 1200 for transfer switch models KCS/KCP/KCC, KSS/KSP, KSSB. This guide is an original work; always confirm procedures against your unit's build record and the manufacturer's current documentation.

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