humidity proplems

[lp14255]

i've changed out an old r-22 AAF classroom unit with its 410a version and now having humidity problems , the units shutting off on temperature setpoint before it takes care of the humidity in the classroom . i read through the manual and theirs nothing in it to program to help.

[beenthere]

Moved to AOP Commercial.

[ascj]

i've changed out an old r-22 AAF classroom unit with its 410a version and now having humidity problems , the units shutting off on temperature setpoint before it takes care of the humidity in the classroom . i read through the manual and theirs nothing in it to program to help.

You got a model number off it?

Normally those units don't have any sort of humidity control. So I would look at infiltration. What's the OA damper doing?

[skippedover]

Is this the same size in Btus'? Perhaps there's an ill fitting sleeve and air infiltration?

[teddy bear]

Anything that results in a cooling coil that is not cold enough to remove the moisture from the air will raise the indoor %RH. A properly charged system with the right amount of air flow over the coil will remove moisture. Excess fresh air infiltration will also raise the indoor %RH. A 45^F coil temp is minimum to get to a 75^F, 50%RH, 55^F dew point. Classrooms with 30 occupants and 400 cfm of fresh air are difficult to maintain <50%RH. This could be 20 lbs. of moisture per hour.
If these spaces are wet for extended many days, expect mold to grow. We have several schools that do the best they can when occupied. They operate dehumidifiers when unoccupied to maintain <50% RH. The make-up air is off and the a/c is off when unoccupied.
Regards TB