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My apartment, which I own, is split upstairs by two hallways. Each hallway has its own A/C unit, to cool 6 single person rooms each. Recently the south side A/C broke. I have called the repairmen out a few times and a couple days after they leave there's another problem, in the mean time the residents are complaining of the heat.

My question is, can I buy an air duct and connect the North and South hallway air conditioning ducts together? At least until I buy a new unit, or get it fixed.

(Yes, we called a different A/C repair company.)

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Seems to me that you would spend more time and exercise trying to schlock in a bypass duct from the still working unit rather than simply just getting the proper replacement for the non-working unit. Keep in mind that the duct idea is also going to put quite a bit of extra load on the existing unit and could end up causing it to fail too. –  Michael Karas Sep 3 '13 at 5:09
    
@MichaelKaras Thanks, I was wondering if it would cause the working unit to have a higher load. My thought was I could spend 1 hour to put in this patch, have the residents happy, and when the repair man comes by next week it'll be fixed. –  Michael Ozeryansky Sep 3 '13 at 5:38
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The majority of the extra "load" on the single existing A/C unit will come from the necessity to run it longer so that it can cycle enough cooling air to both sides of the building. There could be some problems figuring out the thermostatic controls for the single unit over the dual unit setup so that it would cool the currently broken side adequately. –  Michael Karas Sep 3 '13 at 12:50

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It won't hurt anything as a temporary fix. The existing one side of the AC system will have about the same cooling capacity, but each side of the apartment will now have one-half the cooling capacity, assuming the same amount of air is delivered to each side which is unlikely given the extension and turns needed to jumper to the other side (extra pressure drop). The AC will run longer, and will probably not even meet the thermostat set point so will run continuously. If it does ever turn off, say at night, at least the system hit the Tstat set point. This could also result in the tenants on the good AC side complaining since there will be less cooling there. I agree with @Michael Karas, get the broken one fixed as soon as possible to avoid the extra work. If you choose to do this, and this duct is out of sight, put a damper in the extension so you can open/close as needed in the future. Replace the filter at the bottom of the broken unit with cardboard to restrict air from flowing backwards through the broken unit.

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Is there a common return system? If there are separate return ducts, they may need to be jumpered together as well. –  TomG Sep 4 '13 at 1:17
    
I was actually thinking about the damper in case this happens again. But I decided to just go with fixing it correctly. Thank you for the answer, I couldn't find anything close to what I was thinking of doing searching with google. –  Michael Ozeryansky Sep 4 '13 at 6:37
    
I don't think a near 100% duty cycle is healthy for the condensing unit, the blower motor, or nearly any other part of the system. There is no way to say for sure; based on the information provided, that doing this "won't hurt anything". –  Tester101 Sep 4 '13 at 17:27
    
The system is running now isn't it? Of course if one of the components is at the end of it's life then it will just fail sooner. So again, you won't hurt anything by doing this. FYI, I've been testing AC systems for 25 years. –  Richard Raustad Sep 5 '13 at 12:13

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