new air conditioner increases humidity, outside it is 55% - in a room not air conditioned it is 55% - in the room with the air conditioner it ranges from 57% to 64%. It does this even if i open bathroom to increase area or open large slide door to another room of equal size ( doubling the area). It's not to big for the combined rooms because it does not fully cool the other room. I am also running it with the fan speed at low.

 

Welcome to the forums.

What's the temperature in the rooms? Humidity is a relative number pertaining to how much moisture is in the air compared to how much it can hold. As the temperature falls, the amount it can hold decreases as well and therefore there can be less moisture in the air and yet show a higher humidity level.

 

the temperature in the air conditioned room is 75 to 78, in the non- air conditioned room it is 84.

 

Take a can of cold pop out of your refrigerator. It will eventually get sweat on it. (100% humidity on the surface of the cold can, even though it's 55% in the rest of the room). I'm not surprised the air conditioned room shows a little higher humidity. With no vapor barriers between rooms you won't ever "dry out" a room that is being air conditioned.

 

You need another floor type fan to circulate the air; I like the "Wind Machine 3300." I cool three 1st floor rooms plus the hallway & stairwell with a little 6,000-Btuh half ton window A/C.

Gets humidity usually to 50 to 55% & temp to 76-F down to 72F at times & less than 50% RH; with air movement it is very comfortable.

The other comments on the humidity differential, are on target.

You didn't state the outdoor temp!

At 90-F outdoor air at 55% RH holds 119- gr of moisture per lb of dry air, at 200' elevation.

At 76F indoors 65F wet bulb; 55.88% RH; holds only 75.8 gr of moisture per lb of dry air.

119 - 75.8 is 43.2 gr of moisture differential difference to be removed from infiltration air.