In today's short podcast episode, Jim Bergmann and Bryan answer the age-old question: Can you really freeze water in a vacuum by pulling down too fast? Is that a problem? What should you do about it?

Here is the short answer: NO. You CAN'T freeze water in a vacuum in a typical residential A/C system.

First of all, you would need to have water in the system to freeze water in the system. We typically don't see large amounts of water in JVAC systems, but there could be moisture in the evaporator coil in refrigeration. Coupled with the very low temperatures, you could see freezing under vacuum in those systems.

However, you will almost never see freezing moisture under vacuum in residential comfort cooling. On top of that, you would need to have enough water to freeze, not even considering the vacuum speed. We cannot achieve a vacuum that would cause that much water to freeze in a system.

When you perform a decay test, the pressure rise will taper. (If it doesn't rise, then you have a leak.) When the pressure tails off, you've likely come across moisture in the system. You can usually remove that moisture without having to worry about freezing; that moisture will merely exit the system under vacuum, and it typically will not freeze.

But what about water in a normal, non-HVAC vacuum? Can you freeze water in a vacuum then? YES.

The water would vaporize before it freezes, and it would sublimate off very quickly on most vacuum rigs. You can check out this article and video to watch an experiment in action.

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