I'm a commercial winemaker with limited refrigeration knowledge. I believe I have a stuck valve on a French made champagne bottle neck freezer. There's no pressure in the capilary tube to trigger the cut-in contact. If I manually close the contact, the compressor starts. I've tried open and closing, and tapping the valve. Is there any way to unstick a valve short of draining the refrigerant (404A) and taking the valve apart?