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I have two AC Units. One for upstairs and one for downstairs. The upstairs one works just fine but not the downstairs. So, i did a test by turning both units on and went outside to compare the two units. The upstairs one works fine and blows out warm/hot air, but the downstairs one seems to blow out cold air compare to the working unit. These two are not heat pumps. They are both AC units. Anyone know what is wrong with my downstairs unit?

BTW: I had the HVAC guy come out to check it 3 years back, and he added refrigerant into the system. It worked for a week or two after he left, then it's back to warm air again. Would this be a leak of some sort?

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3 Answers 3

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Because of the need to capture the refrigerant and licenses to get the refrigerant in most places, this typically isn't a DIY job. The fact that the outside unit is running and air is blowing inside suggests that it's not a problem with the thermostat. Check the breaker, air filters, and any other easy to access components for obvious problems. Beyond that, there are a lot of possible issues:

  • Compressor has failed
  • No refrigerant or not enough
  • Capacitor has failed
  • Controller has failed or wiring has become disconnected
  • Inside coils have frozen over
  • Reversing valve on a heat pump isn't activating

The first two are the most likely and either will need a professional to repair. Capacitors can be checked with a multi-meter. Controllers and the thermostat are switches, connecting various components to the hot side of the 24V transformer. Issues with them can be ruled out by jumpering the appropriate connections. If you don't have a heat pump, or the air from the vent isn't measuring as warmer than the return, then it's unlikely to be the reversing valve.

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  • added new information. do you think it's caused by refrigerant leak?
    – KJYe.Name
    Mar 23, 2012 at 17:04
  • @kjy112, sounds like a leak to me. The refrigerant is also a lubricant for the compressor, so they typically shutoff for safety when you're low on refrigerant. Otherwise, it's a bit like driving your car without any oil. Anyone that doesn't attempt to locate and resolve the leak isn't worth hiring.
    – BMitch
    Mar 23, 2012 at 18:47
  • thanks for all the advice. Do you know how much it costs normally for locating and resolve leak? I live in Atlanta, GA.
    – KJYe.Name
    Mar 23, 2012 at 20:14
  • @kjy112, no idea, but once the lines are pressurized, locating the leak shouldn't be too hard. All you need is some soapy water on each fitting until you find the one that's bubbling.
    – BMitch
    Mar 23, 2012 at 20:53
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    Update on this. I was told compressor died and there was a refrigerant leak prior. Need to replace :(
    – KJYe.Name
    May 23, 2019 at 20:50
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Definitely a leak of Freon. The Technician should have first started by pinpointing the leak before recharging your system with more refrigerant

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    The OP has already responded and said there was a leak. The leak was also mentioned in a previous answer.
    – JACK
    Apr 15, 2023 at 23:34
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It's either a dirty unit or a capacitor problem. If the unit is very dusty you need to clean out the dust to let it breathe. If the capacitor went bad, when you look at it the top will be bubbled up. Most likely it's the capacitor.

Change your filters: a dirty filter is what an AC mechanic loves; it's money in the bank for him.

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