Closing off ducts bad for AC Unit?

[willfeeny]

We just bought a 2 story zoned heating and cooling with 2 AC units and 2 furnaces. 1 of both for each floor. My question is about shutting off ducts off the main trunk, we have 4 bedrooms upstairs which are cooled off 1 AC unit, we only use the master bedroom. The others basically just have boxes at this point. I have read it is ok to shut off the ducts somewhere, and then another source saying it makes it harder on the AC unit. I would like to close them all except the ones going to the master bedroom and master bath.

We had the units inspected and cleaned and the HVAC guy said our units are very large for the house. I have no idea, I got the models #s and it looks like the unit for upstairs is a 3 ton Goodman which is newer and the older for the main floor is a 2.5 ton Rheem. The house is 3,100 sq ft.

Then AC unit upstairs is able to cool off the master to a nice temp in only 2-3 hours. I turn it on a few hours before we go to bed and turn it off all night and day just because I hate to cool the entire upstairs all day and night when it is not being used. and the temperature reading is taken out in the hall so it would have to run a while, we are looking to have it moved into the master bedroom or get a remote sensor.

I just figured if we shut off the other ducst we would get more air coming into the 1 space we need it and I could run it even less. Closing just the vents in the rooms doesn't seem like it would do much. Don't want to do it if it will hurt the unit though.

Thanks

[dnt]

Probably just shorten the compressor life a bit, if the flow is restrcited it could cause some compressor liquid slugging but if it utilizes a scroll compressor it can take a lot of abuse. If you planned on using it this way for a long time I would have someone adjust the charge level to better match the airflow conditions. Partially closing the vents might be a better solution, that way you are not completely restricting the flow close the doors and you will still have some savings from not bringing the other three rooms down to the lower temp besides you do not want the boxes to spontaneously catch fire from excessive heat in those rooms LOL.

[willfeeny]

Probably a good idea, think I will take your advice and partially close the ones we don't use. I need to get down there and seal a lot of the ductwork as well, air is pouring out in most places.

[markwolf]

heat rises......leave the upstairs all open.set the downstairs to a higher temp imo.

[Irascible]

I could give you a multi-paragraph reply covering all the variables. The bottom line is that you simply don't know what effect closing vents will have on the system. It may end up being harmless to the system and save you a few pennies. Or it may save you even fewer pennies than you think and ultimately kill your compressor. Which will it be? Roll the dice and find out I suppose.

[willfeeny]

Well I wasn't trying to shut them off to save a few pennies as I was to just try and get more air coming into the master bedroom. I guess that is trying to save so I can run it less, but its more to just get that room even cooler and cooler quicker.

[Irascible]

Fine. You're not trying to save a few pennies. That wasn't the point. :p

The good news is that air conditioners are generally pretty tough. If there is any negative effect on the system from what you're doing it will probably handle it. I expect that it will. Or it might not. Which will it be? You'll find out.