Ice on the ceiling of a walk in

[stat]

Ever wonder why freezers have heated vents? It’s to avoid drawing a negative pressure on the box when the door is opened and warm air rushes in, then is quickly cooled and thus takes up less volume. Freezers tend to be their own little low pressure zones if you will.
At an extreme case, I had a box located outdoors that had an untrapped drain. It would pull humidity in so bad it would build ice on the fan guards and either freeze the blades in place or break them altogether.

Seen WIFs that the door could not be opened until the air pressures equalized.

We normally put a delay timer on the fans connected to the door in that case.

I am familiar with heated vents.

[swift one]

I have heard this for 30 years. Worked on many WIF without trapped drains. Never seen it cause an issue.

That's just me though. YMMV.

[5-Wyres]

It would be nice if the users listen to us techs because shutting units off at disconnect is wear and tear on units

[Gleng]

Make sure the X wire takes the unit out of defrost ,before the heaters get hot enough to form steam.the steam will get on the ceiling,Drip on the floor.create ice on the ceiling and floor.Make sure the coil is good and frosted before the fans come back on.I have had to add separate defrost thermostats to get the coil to frost enough and not blow water off the coil.

[mcr]

How's this beauty. Stat set to -25, fan delay not working and they prop the door all the time. There is a steam kettle about 6 feet away from the door!

[HVAC/R 19]

How's this beauty. Stat set to -25, fan delay not working and they prop the door all the time. There is a steam kettle about 6 feet away from the door!

At least the ceiling is now fully insulated.

[crazzycajun]

Last time I seen stuff like that drugs were involved

[koolkahuna]

Defrost Termination Fan Delay switch not working properly. Coil has to freeze the moisture onto the fins before the evap fan(s) start(s). This is to eliminate blowoff of moisture into the box which will accumulate on the ceiling and other surfaces.