Temperature chamber and humidity

Regarding temperature chambers and how to use them...
For years it has been my understanding that you should do the "hot"
part of temperature tests first, so that the chamber air will "dry out". Then, when you do the "cold" tests, there will be no condensation in the chamber.
OK, so here is how I do it... -- put the UUT in the chamber with the door open -- close the door and raise the temperature -- let it stay hot for something like an hour -- reduce the temperature as cold as you like
Now the question: where did the moisture go?
When you start, the chamber is full of room-ambient air, complete with moisture. As it gets hot and cold, the air leaks out or back in, but it is still the air from the room, with the same relative humidity. Why did the air get more dry?
My reason for asking is so I can reduce the "one hour hot time" and reduce the time it takes for the test sequence.
Any comments will be appreciated.
Kevin
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Find a reliability engineer and/or a good book on temperature testing and find out how it's down. It's too complicated to describe in a post.
Al
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It didn't. Heating air lowers the *relative* humidity, but not the *absolute* humidity. The amount of moisture in the air (grains per pound of dry air) is the same. Since hot air can 'hold' more moisture, the ratio of actual-amount-of-moisture versus amount-of-moisture-could-hold goes down (RH).
Mind you, heating up the equipment will tend to drive moisture from the surface or whatever coatings into the air, so the *device* might dry out somewhat.

Well, here I have to defer to 'Al'. Specific test requirements may have to be met, regardless.
daestrom
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Kevin, I do it exactly opposite. I like doing cold first, so that when we're done we come out of a hot cycle and there is no condensation on the unit.
M Walter
Kevin Kilzer wrote:

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