Baldwin Coolers and Chillers for CEMS

Baldwin™-Series Model M325D Thermo-Electric Cooler Troubleshooting and Maintenance Guide

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Troubleshooting and repair should only be attempted by qualified personnel;
Review Safety Warnings Page for more complete details of potential hazards

Inside the enclosure there are lethal AC voltages, 15VDC power at 16 amps, as well as exposed rotating fan blades and other potentially hazardous components.


The display and LEDs will indicate what the on-board computer thinks is happening.
Verify that the unit has commanded the response before going in to verifying hardware. For example, verify the board indicates that the pump relay is closed before physically pulling the relay.

Peltier Elements

Troubleshooting Peltier elements can be difficult at the part level without specialized equipment. A conventional Ohm Meter will not provide useful information. Peltier failure or degradation can be indicated by current measurement. The measurement should be made during the first few minutes of start-up. For the M325D, the Peltier elements are wired individually. Unit-to-unit variation, such as exact voltage, wire run length, ambient temperature, and cooler temperature, can generate some variation. Testing can be performed by placing a DC inductive ammeter around the black or white leads coming off JP10 or JP11.

Properly functioning Peltier elements should draw between 6 and 9 amps each (with the cooler at room temperature; which is maximum loading). Greater than 9 amps indicates a partially shorted Peltier; Less than 6 amps indicates a partially open Peltier element. In either case, retest before replacement to verify results are consistent.

12VDC Cooling Fan

There are two regulated outputs for the 12VDC cooling fan, one is thermostatically controlled by the control board. The 12VDC cooling fan on a 125D should be wired to the designated 12VDC output of the board. Care should always be taken to avoid rotating blades!

Symptom Diagnostic Fix
No LED(s) and no fan.

AC power input.
10A DC fuse on Control Board

5A AC Input fuse in Power Supply (remove PS cover to locate)

Verify 15VDC at output terminals on Power Supply

Ensure that AC power is connected. Replace fuse as necessary.

  • Verify current draw is not close to or exceeding fuse rating
  • Verify current draw of Peltier Elements (see below)
  • Replace control board if Peltier elements test properly and current is excessive

Replace fuse as necessary.

  • Verify current draw is not close to or exceeding fuse rating
  • Replace power supply if current is excessive
  • If reading lower than 15VDC, carefully disconnect wiring and measure voltage
  • If not 15VDC, within 1.0VDC adjust and/or replace defective Power Supply

LED(s) on and heatsink fan does not run.

Check fan for blockage (power off). Check for power at JP1 (AC power input, unfused).

Clear any blockage, replace fuse or repair wiring as required

Check fuses on control PCB-

  • If fuses are good and voltage is not equal to line voltage, replace control board.
  •  If fuse1 is blown (open), disconnect JP12 wiring for heat sink Cooling fan and replace fuse; Retest; reconnect wiring if fuse does not blow
  • If fuse blows again, Fan or wiring may be Control PCB defective-Replace
Failure LED is on. Thermistor connection JP15 pins 1-4

Ensure proper connection.
Try a good thermistor in place of old one

  • Mark wiring and connect to opposite channels at control PCB, if failure moves with change of wiring, thermistor has failed

If not, board is defective. Replace as required

Impinger frozen and cooler indicates ambient temperature.

Thermistor placement in heat exchanger block.
Peltier element wiring

Verify placement of thermistor Trace wiring to ensure wiring is not shorted to chassis ground due to pinched wires caught in covers

Impinger does not reach set temperature but is below ready temperature.

System loading.

Verify Peltier Element current draw

Ensure system loading is not exceeding cooler capacity.
Review Specifications
Peltier Elements should draw between 6 and 9 Amps

Ready LED does not come on when impinger is below 10°C. Ready temperature adjustment. Consult Factory
Water carryover in system. Impinger temperature. Should be below 5°C. Ensure system loading is not exceeding cooler capacity and ambient conditions are not exceeding specifications.
Slip LED does not come on. Water carryover in system.

Water slip sensor connections.

Ensure system loading is not exceeding cooler capacity and ambient conditions are not exceeding specifications.

  • Ensure that all water slip sensor connections are made.
  • Disconnect sensor; Clean tip of sensor.

Replace sensor as necessary.

Pump does not start. Ready and slip LED(s) are on. Pump electrical connections. Ensure proper connections.
Possible defective pump; Measure voltage at corresponding pump terminals.

  • If good, pump motor may be defective(open)
  • If bad, fuse may be blown on board; replace fuse with pump disconnected, reenergize and retest. If fuse blows, board is defective
  • Reconnect pump, if it blows pump motor likely defective (shorted or mechanical failure)

Possible defective relay coil or relay contact- Visually check operation and condition. If O.K., check coil of relay with ohm meter; if O.K., possible bad relay contact; Replace with known good relay.

Download Baldwin™-Series Model M325D Thermo-Electric Cooler User’s Manual

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