Overview
When a Leica CM1850 cryostat repeatedly attempts to start but never begins cooling, labs experience immediate workflow disruption. This issue is common on older CM1850 units and can usually be traced to a failed start capacitor in the compressor circuit.
At Rankin Services, we regularly resolve this failure and provide nationwide onsite repair, depot service, and preventative maintenance for Leica cryostats.
Common Symptoms Video
- Unit attempts to start, then shuts off immediately
- Compressor hums, vibrates, or “bumps” but never runs
- Start cycle repeats over and over
- Room lights dim or flicker during attempts
- No cooling achieved / chamber remains warm
Most Likely Cause
Failed start capacitor in the refrigeration system
The start capacitor provides the initial power boost required to start the compressor motor. When it fails, the compressor cannot overcome its startup load and repeatedly stalls.
Why This Happens
The start capacitor handles high electrical current during every startup. Over years of cycling and environmental heat around the compressor, it can:
- Dry out internally
- Lose capacitance
- Short internally or open circuit
A weak or failed capacitor places strain on the compressor and building electrical system.
How to Diagnose
Safety Note: High-voltage components require proper handling. Only trained personnel should perform capacitor testing.
- Disconnect power to the unit completely
- Safely discharge capacitor using a resistor (never short it)
- Remove the capacitor and test with a meter capable of capacitance measurement (µF)
- Compare reading to the rated value printed on the part
If the value is low, reads 0, or shows open — the component has failed.
Recommended Repair
- Replace the start capacitor with the correct value and voltage rating
- Replace the start relay while accessing the compressor compartment
- Inspect the compressor relay, connections, and wiring
- Verify compressor current draw and confirm reliable cold-start operation
Expected Results After Replacement
Once completed, the CM1850 should:
- Start the compressor consistently
- Maintain cooling performance as expected
- Eliminate cycling issues and flickering lights
Addressing the capacitor and relay early helps prevent excessive strain on the compressor, reducing the risk of a much more expensive failure.
Parts Required (OEM-Equivalent)
| Component | Description |
| Start Capacitor | Provides startup torque for compressor |
| Optional: Compressor Relay | Inspect/replace if overheated or pitted |
Order Parts from Rankin Biomedical
Start Capacitor 10483
Start Relay
Repair Time & Skill Level
- 30–60 minutes
- Intermediate electrical troubleshooting
Rankin Services can perform this repair onsite or depot.
Preventative Tip
Include capacitor checks in annual cryostat preventative maintenance to reduce:
- Electrical stress
- Compressor wear
- Emergency downtime
Replacing aging capacitors proactively is inexpensive insurance.
Need Help?
Rankin Services provides:
- On-site emergency cryostat repair
- Preventative maintenance packages
- OEM & OEM-equivalent replacement parts
- Fast nationwide service & depot repairs
Request service at rankinservices.com