About sealing and moisture in a test chamber
Our chambers are insulated and sealed because ambient air and moisture are detrimental to their operation. Moisture will collect on the cooling coil, which is typically the coldest part of the chamber. This moisture can build up as ice. Warming cycles of the chamber will melt this frost or ice, which is why we have a 'condensate drain' on every chamber, with or without humidity control systems. This drain is open and shouldn't be trapped, and thus can let in ambient air as the air shrinks when cooling.
Moisture can also penetrate the chamber liner and collect inside the walls. This not only causes frosting and 'cold spots' on the walls, it dampens the insulation and renders it useless. Our greatest 'test' of our liner seals is running a high humidity test like 85C/85%. This steamy condition is also slightly pressurized because of the generation of vapor gas. In our benchtop chambers, this excess pressure is released out of the condensate drain.
The other possible 'leaks' of the chamber, besides the drain, are the cable ports and the door gaskets. Our own operational penetrations are well sealed with special caulking. The only exception would be the blower shaft, which has a gasket seal, but is sealed on the exterior at the motor. Our cable ports are lined and sealed to protect the chamber line. The doorframes have wire heaters embedded to protect against moisture collection at the gaskets. The compression on our gaskets, when closed, is significant, and for our purposes, it is considered sealed. The customer can seal the cable port on their own, and our closed-cell silicone plugs provide an excellent seal, especially when used on the interior and exterior.
For nitrogen (gas or liquid) or dry-air purge options, we include a separate port for venting the excess gas. This is a cable port with a silicone 'star' membrane on the interior to let the air out (or in). If the purge is not active, it can be a source of moisture during cold testing.
So, we 'seal' the chamber for our normal needs of operation, but allow some exposure to ambient air via the drain and added vent-port. Also, our chambers are not designed to hold a vacuum or pressure.