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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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up vote 7 down vote accepted

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
  • Controller has failed or wiring has become disconnected
  • Inside coils have frozen over

Since the first two are the most likely and either will need a professional to repair, you may as well get one out to diagnose the problem for you.

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added new information. do you think it's caused by refrigerant leak? – kjy112 Mar 23 '12 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 '12 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. – kjy112 Mar 23 '12 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 '12 at 20:53
thanks BMitch will keep the post updated – kjy112 Mar 24 '12 at 0:30

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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