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The Earth started cooling about 4 billion years ago.
Cold tubes cause condensation moisture, and if you put the gases in the tubes from a compressed source, expanding gases cause cooling (due to entropic effects).
Do you mean a Heater Control Valve...
Reasons for low vacuum:
1. Low gland sealing pressure
2. Condenser tubes choked
3. Condenser cooling water temperature high
4. Leakage in condenser tubes
5. Less cooling water flow