Hello, i have some questions that i just can't seem to find or figure out the answers to and hopefully you can help. I recently bought a Frigidaire FFRA051ZA1 5,000BTU window air conditioner. For a 150 sq ft bedroom occupied by 2 adults 1 infant and 2 dogs. My window around the unit is completely sealed the HVAC vent in the room is sealed and the door is kept shut and i have noticed a humidity problem i never before had. When the compressor is on it dehumidifies the room say down to 50 percent once that compressor in the unit kicks off ill watch the humidity percentage rise drastically on the digital thermometer that i have. I'll watch it rise probably 10 percent within maybe 20 mins when the compressor kicks off. So say 60 percent humidity now and compressor kicks on and brings in down to 55 then compressor kicks off and humidity rises to 65 and so on and so forth until it's in the 70s. Theres no running water in here no bathroom nothing to give off moisture. Before i had this unit and was using the HVAC system the temp would be set to 76 and i would keep the door closed on the bedroom but it would get hot in here up to 81 degrees before i couldn't take it and had to open the door. BUT humidy would stay around 55%. I've had this window unit bring the temp. Down to 70 degrees and humidity would be 60 percent or more. I have gotten the temp down to where i like it and manually turned the unit completely off and the humidity would rise a little bit but not as drastic as it would if the compressor turned off and the fan stayed running. The humidity only drastically rises when the compressor stops running and the fan continues running. I also thought this unit was bringing in the humidity from outside when the fan stayed on after the compressor turned off until i found out that this unit has a closer vent system meaning it recirculates the bedroom air not bringing in any outside air. Which now has me so confused as to what is happening and why the humidity rises drastically once the compressor kicks off and the fan stays running. Why do you think this is happening? Will a different window unit solve my problem?

 

Moisture is probably entering the room through the walls, floor and ceiling. That's why when the AC compressor turns off you see the humidity rise. If you want to reduce humidity beyond what the AC can provide you might need a dehumidifier. You can also look for another (probably more expensive) AC unit that has a dehumidify setting. It will still cool the room but instead of being optimized for cooling it will focus more on moisture removal.

 

I can understand that. But i don't understand why it only started once i installed this window unit. Never had a humidity problem until i installed this unit.

 

If you already have central heat and air conditioning closing off one room and adding a window AC can throw things into chaos. Window units typically are not sealed all that well. There are usually numerous gaps and cracks where outside air can enter. It can be made worse if the house still has a working central AC system that may be drawing outside air in through your window unit.

Sometime when you are bored use a cigarette, incense or blown out match or candle to make some smoke. Hold the smoke source next to your window unit when it is off but the house's central AC is running. Try the test by holding the smoke near the bottom of the room's door. You might be surprised at how much air is actually moving around even though you think things are sealed up tight.

 

you cant leave the fan running. Those dampers that recirc the air is just a flap thing.. Your letting in outside air coupled with the fan running..

ideally you want that ac running non stop on low fan compressor on. That will remove the most moisture. But you need an ac that will turn itself off and on..

Your best bet for that room is just add a return duct to that room and tie it into the return of the main AC and your issues should go away..

 

Does this make sense? Your breath adds humidity. Before you got the room air conditioner the central A/C cooled the entire house and its fan then continued to commingle the room air with the rest of the house. Now, with the room A/C, the central A/C was shout off and all of the humidity from your breath stays in that one room.

 

Ok.
You do not have a humidity problem.
The reading you are using is RH which stands for relative humidity.
This means that the reading you get is the % of humidity you have in the air at it's current temperature.
As the air conditioner lowers the room temperature it has less ability to hold moisture which is why the RH is lower.
IOW you have the same grains of moisture per lb
of air with a % reading based on how much moisture the air can hold.

The best place for your hygrometer is inside a drawer. 😊