Most commercial and consumer products are tested and verified in non-condensing humidity environments, which verifies the ability to withstand operating in ambient atmosphere with a high moisture content.
Military and Aerospace products however, are often required to operate in a climatic testing environment where moisture will condense in liquid form directly on the product. This is NOT a test you want to immediately run with out doing some pre-test work.
For one thing, a product has to be designed to withstand this very severe environment. (How to do this could be the subject of another post.) If you “think” your design is good, now go on to some “pre-checks”.
Start by examining all of your conformal coated electronics, in detail under a UV light. Look for small voids. If you have them, you need to revisit your coating process. You would have failed your humidity reliability test.
Next, go the garden supply store and buy a plant mister.
This device will put out a very fine mist, and when applied to a surface, it will produce a similar effect to condensing humidity. Use plastic sheets and tape to mask off parts of your system, and apply the mist to each circuit board individually, while operating. This will help find vulnerabilities with out having to actually use a humidity chamber, and you will know immediately which sub-assembly needs to be changed to get through this test.