My downstairs ac unit stopped working. My upstairs unit is still running. Will my upstairs unit work harder? Upstairs is smaller unit. Downstairs is the main unit


3 Answers 3


Not really work harder.

It usually works at maximum capacity anyway.

But it will work longer since the thermostat upstairs' will not report cool down.

It just means you will use more electricity.

Let's talk about the AC that is not working.

Could be just the thermostat, or just the circuit breaker.

Testing the circuit breaker is easy.

Testing the thermostat is bit more complicated. It depends what kind is it.

  • Thank you. I was just worried the ac upstairs will break down too. Jun 14, 2022 at 1:33
  • No it wont, it should be fine running all the time.
    – Traveler
    Jun 14, 2022 at 1:38
  • @CynthiaWilliams lets try some easy fix for the AC, find and trip the circuit breaker (off/on)
    – Traveler
    Jun 14, 2022 at 1:42
  • @CynthiaWilliams listen to your Thermostat very carefully, then change the dial. Do you hear a click? If they are one of the modern one, you can unplug without removing wires, exchange it with the upper thermostat.
    – Traveler
    Jun 14, 2022 at 1:45

Here's the thing. Cooling is not equal on a building. The heat you're trying to remove doesn't come from "outside"... it comes from 3 places.

  • Solar Gain. Every square foot of sunlight hitting your house adds 150-300 BTU/hour of heat to your house that your A/C must remove. (depending on angle and paint color). The worst is roofs, which have an albedo of about 5% (95% absorbed so adding 320 BTU/hr to your house.
  • Humidity leaking in from outside. Because of the way humans sweat, humidity feels like heat and dry air feels like air conditioning. That means if air leaks are letting humidity into the house, it will feel warmer than the thermometer says, and removing that humidity will steal capacity from the A/C. (970 BTU per pound of water removed).
  • outside air warming the outside of the house, and that heat working its way through insulation. This will be a problem even on the north side of the house, but all in all this is not as big a problem as the others.

So it depends on your house's layout. If most of the solar gain falls on the upstairs, it could be that most of the important air conditioning happens up there.


Without knowing what kind of AC or what capacities, and the square footage of the building, who can say?

Most likely, the upstairs unit is not sufficient to cool the entire place, or else you wouldn't have 2 ACs. So it's quite unlikely that the upstairs AC is going to cool both floors.

If you limit the airflow from upstairs to downstairs, it shouldn't have to work much harder, since it's still only trying to cool the upstairs. Though heat from the now hot downstairs will rise upstairs and it'll have to work a bit harder. If there's no doors in the way blocking hot air from rising upstairs, it may have to work a lot harder, or just not be able to keep up and cool the place sufficiently.


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