The Leica CM1850 cryostat is relied on for steady, dependable cooling during frozen sectioning. When the unit powers on but fails to cool, it can disrupt your whole MOHS surgery schedule. One of the most common causes of this issue is a failed solid state relay that prevents the compressor and cooling fan from receiving power. Rankin Services encounters this failure frequently and it is often overlooked because the cryostat appears to operate normally and typically displays no error codes.
What You See When the CM1850 Is Not Cooling
A failed solid state relay creates a very specific set of symptoms. The unit appears to start correctly and the display looks normal, yet the refrigeration system never engages. Common signs include:
- The compressor does not start
- The cooling fan does not run
- The chamber remains at room temperature
- Typically no error codes appear on the display
This can be confusing because the logic board still powers on and the interface responds normally.
What the Solid State Relay Does
The solid state relay is an electronic switching device that enables the compressor and cooling fan to receive full line voltage. The logic board sends a low voltage control signal to the relay. When the relay is functioning properly, it closes the circuit and allows the compressor and fan to turn on.
If the relay fails in an open state, the control board may still command cooling, but the power never reaches the refrigeration components. The result is a cryostat that appears active but provides no cooling.
How to Confirm a Failed Solid State Relay
You can verify this issue with a few basic tests.
- Turn off and unplug the CM1850
- Remove the rear panel to access the solid state relay
- Power the unit back on with appropriate safety precautions and personal protective equipment
- Measure the low voltage control signal at the relay input terminals
- Confirm that the controller is sending the 5VDC signal when cooling should be active
- Measure the AC output side of the relay
If the control signal is present but the output side does not allow voltage through the relay, the relay is not closing and must be replaced. This test is one of the most reliable ways to diagnose a Leica CM1850 cryostat not cooling due to relay failure.
Why the Solid State Relay Fails
Solid state relays commonly fail in devices that use compressors. The initial startup of the compressor creates a sharp inrush of current, often reaching 45 to 50 amps momentarily. Over time, these repeated surges weaken the internal switching components of the relay. Eventually the relay becomes stuck in an open state and can no longer pass line voltage.
Heat stress, loose terminals, and gradual electronic breakdown can also accelerate failure.
Replacing the Solid State Relay
When replacing the relay, follow these guidelines:
- Match the DC control voltage rating
- Match the AC voltage and current rating
- Ensure proper heat sinking or thermal compound if originally used
- Use the same mounting pattern and terminal style
You can purchase the correct component from Rankin Biomedical at:
https://www.rankinbiomedical.com
Why This Issue Matters
When the solid state relay fails, the entire refrigeration system is disabled. The compressor and evaporator fan never activate and the cryostat cannot cool. Because the logic board still powers on, the problem is often misdiagnosed as a controller issue. Understanding the role of the relay can prevent unnecessary part replacement and reduce downtime when a Leica CM1850 cryostat is not cooling.
Proactive Maintenance Considerations
During routine preventive maintenance, you can evaluate the relay for early signs of stress:
- Check that the control board is sending a signal to the relay when cooling is requested
- Inspect the relay body and terminals for discoloration or heat damage
- Note any unusual heat from the relay when it is under load
- Confirm that all wiring connections are tight and free of carbon buildup
Identifying early indicators can prevent unexpected cooling failures and unplanned interruptions in service.
Summary and How Rankin Services Can Help
If your Leica CM1850 powers on normally but does not cool, and there is no sound from the compressor or fan, the solid state relay is a likely failure point. A simple voltage test will confirm whether the relay is stuck open. Once replaced with a properly rated component, the cryostat can return to normal cooling operation.
Rankin Services can assist with diagnostics, relay replacement, and full functional testing to ensure your Leica CM1850 cryostat not cooling issue is resolved correctly.
You can request service through the Rankin Services service request form at:
https://rankinservices.com/service-request
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