i just bought three new ac units a 6500 for the master 8000 for the office and 18500 btu to do the whole main level. installed 6k and 18k units. the main level is 1000sq.ft temp was 75 in the room and 90 humidty. turned it on and with in about 30 mins it was at the set temp of 70 degress and humidty was gone. and it works great and i only used it twice so fair. the master is the problem one. The room is about 175 sqft with the bathroom. last night 74 in the the room humidty 90% turn on the ac, the ac turns off about 20 mins later the humidty is still there and the temp did go down to 70. but it dose not feel like the main level. turned the temp down to 68 ran for 15 mins and turned off did not seem like it got any cool and did not take out the humidty. but the ac is dripping water. is there a problem with the ac? or is it to small for the room. should I try the 8k and see how it dose and buy a 10000 for the office. But thats double what the ac sq ft chart says. I do leave the door to bedroom opened so I closed it last light to see and its the same. the up stairs about 1100 sqft and the office is one of the bedrooms. if i use a 8 and 10k unit up there. do you think it will cool the other two rooms, hall and bathroom? I have ceiling fans in every bedroom and hall too. and the fan in the master was running with the ac on last night. I have run this unit three times and its the same thing every time just like last night.

thanks

 

Because heat rises, upper levels are more difficult to cool than lower floors.

That said, two questions: Can you install the unit in the office so that you're cooling the entire floor? And what's above the second floor ceiling? Is there an attic, and is it both well-insulated and well-ventilated?

 

The house is a split and I can up the office ac in. Im going to put it in this weekend. I just put the big one in this wed. 8' ceiling all floors. and the bedrooms are on the south side. attic is above the bedrooms. its vented with ridge vent, sofets. and i do have a attic fan up there that runs. insul. is ok. i have to work on that. its r19 and somebody put r19 on top again. my plan is to take it all out and blow in r50 up there. but in the fall.

 

The ventilation sounds OK, depending on the area of the soffit intakes. Not sure what the attic fan is for.

Sounds like quite a bit of insulation now. Just curious: Have you used a tool such as the ZIP-Code Insulation Program to figure out how much insulation you need, and where?

If you do decide to blow in new insulation, I hope you have a way in mind to keep it from blocking the soffit-to-ridge air flow. As you may already know, effective ceiling insulation depends on eliminating condensation, which is what the venting is designed to do.

 

The A/C in the bedroom is too large, pure and simple. Air conditioners work off of temperature, not humidity and when the temperature at the thermostat sensing bulb reaches the set point the unit stops, or at least the compressor will stop.

Dehumidification requires a relatively low airflow across the evaporator (cooling) coil but having the room air fan moving slowly also allows the evaporator to cool to below 32 degrees F. and that causes the water (from the air) to freeze on the coil thereby blocking all air flow. Having a smaller rated A/C keeps the evaporator from getting too cold while still having the relatively low airflow needed.

One thing that might help is a baffle to keep the cold air outlet from the unit from immediately falling and being sucked into the inlet. I have one unit that all it required was a sheet of 1/2 inch rigid foam insulation jammed in below the air outlet and extending about 18 inches. The unit in my bedroom I bent a piece of sheet metal to direct the outlet air upwards. Neither of these methods are pretty nor are they ideal but they do work for me.

 

Furd beat me to it - yep, classic behavior when the AC is too big for the space.

 

my code is r38 up in the attic. but the first batt is from1960 and its getting flat and its not double everywhere. yep I know somebody already put those foam boards for the soffit. the fans there to get the heat out I guess it comes on ehen it hits 80. I turned it off it use a lot of power to run.

well I know what you guys are saying with it to big. the big 18500 is made to cool 1190 the main floor is only 690 sqft . becuase I figure for party snd the kitchen plus it dose go down to family room and that's 490 sqft.

update the ac is bad. its was 83 today but the big one on at 72 cooled it down from 76 in 20 min. put the bedroom on at 70. it was nice and cool down in the main level. the bedroom felt a lot hotter hall temp was 78. I took the temp of the room and is was 75 the ac therm. is messed up turned it down 66 snd its hold at 72 in the room right now. and the ac turned off. got them set to eco mode. ill return it and get another one tomorrow and see and going to put the office one in too. its going to me 90 tomorrow, that's just crazy for here in ny.

 

I am going to assume that English is a second language for you. Your lack of writing skills makes it hard to decipher what you wrote but it seems as if you are ignoring what we wrote about the A/C unit in your bedroom being too large.

 

Sounds like all the units are over sized.

 

if there over sized then why did they not keep up yesterday? it was 90 degrees out. the main level ac was fine, even with the oven on. it kept it down right at 72 where i had it set. both ac where running up stairs and they kept turning on and off. it was like 74 in both rooms and it went up to 80 in the hall way upstairs.

 

Have you ever considered suing the school where you failed to learn how to write?

The A/C unit is oversized because they are short cycling rather than continuing to run. They are (NOT there) blowing out cool air which is immediately being sucked back into the intake, over the thermostat and then shutting down because the THERMOSTAT has determined the temperature is at the set point. Running the room air fan at high speed will help some but probably not enough. You might try using a box fan pointed towards the A/C to blow the cooler air away from the unit and also bring warmer air to the intake.

OR, you could do as I previously advised and try adding baffles to direct either the discharge air or the intake air. Anything to keep the cool output air from going back into the intake will help. Just don't baffle to the point of restricting the airflow.