This procedure is discussed in the decon and CTI 1050C manuals on this page: IGRINS Cooling System Information

In Summary:

1) Operate the coldhead for 1-3 hours. This freezes, the contaminants out of the helium circuit and into the coldhead. 

2) Shut down the helium compressor and immediately connect the maintenance manifold in its place. We try to disconnect the hoses at the coldhead to use the short hoses and reduce helium gas waste. If short hoses are not available, then disconnect at the compressor and install the manifold there.

3) Reduce the pressure in the coldhead to 30-50 psig. Don't go below 30 psig.

4) Allow the second coldhead stage to warm above 275K. This temperature is tracked in the electronics rack. Expect to wait 12 hours.

       Note: This is a good time to put IGRINS on the vacuum pump. Once the coldhead is clean, cooldown can immediately start if IGRINS has been on the pump for at least 2 hours. 

5) Attach the regulator to the helium tank and purge the line for 10 seconds. Attach the fitting to the regulator with gas flowing.

6) Now you can clean the coldhead:

• Set the regulator on the helium tank to 210 psig.
• Open the Hoke valve (the black knob) to pressurize the coldhead and maintenance manifold to ~200 psig.
• Close the Hoke valve.
• Open the ball valve (handle) to depressurize the manifold to 30-50 psig. Don't go below 30 psig.
• Repeat at least 10 times. The manual says 25.
• The manual also says that for every 5th flush, run the coldhead for 10-30 seconds. This would be done by switching on the compressor even though the helium lines are not attached to the coldhead. This step is done with the coldhead pressurized to 200 psig.
• Finally, pressurize the coldhead back to 200 psig.
• Close the helium regulator.
• Disconnect the helium hoses from the manifold.
• Return the coldhead to its normal operating setup.

The cooldown can be started if IGRINS has been on the vacuum pump for at least 2 hours.