Hi all. Thanks in advance for any advice you can offer, and apologies for the length. This is seemingly an extremely unique, complex, and frustrating problem. I'll do my best to describe as briefly as possible -- please feel free to ask any clarifying questions you find necessary.
My wife and I live in a typical 1400 sq ft suburban house in Atlanta, with a 2.5-ton AC unit. House is 13 years old, and until a few weeks ago, all HVAC was original equipment. Two storeys, with an open living room to second floor. A/C system is NOT zoned. Plus our master bedroom is over the garage, and faces south. So our upstairs (especially master) tends to be 5-10 degrees warmer than down.
Thermostat is downstairs, and we like to sleep cold, so it's usually set to 65 or 66 down at night, so we can hit 68-ish upstairs (ideal sleep). Then when we wake up, we set it to 70 or 71 (wife works at home and needs it comfy in upstairs office), and it usually doesn't run again until midday. This has more or less worked fine until the last 8-9 months...
The old system had been running more or less OK until August 2011, when we discovered it had a freon leak. Had it topped off at that time -- but just a month or so back (only 7 months since top-off), it was already down 3 pounds, and freezing up again. At that point, we decided to replace the coil and outdoor unit with a new R410 system, rather than trying to repair an old R22. New equipment is Ruud, still 2.5 ton. We assumed this would solve our freeze-up issues, and independent professional opinions agreed with that.
Unfortunately, the regular freezing-up has continued on the new system. Our contractor has been GREAT -- he's been back out several times at no charge to try to diagnose this, but with no success. He calls this a "one-in-200" type problem. He's basically tested everything he knows could cause freezing, and nothing is wrong. Literally everything he's checked is working like clockwork.
Here is what has already been ruled out, both by me as well as my contractor:
* Refrigerant leak. My guys have vacuum tested the whole system -- coil, outdoor unit, line set -- at least twice. Waited for over an hour to see if the needle moved, it didn't. Checked the charge again after over a week, no change. No leaks.
* Insufficient or collapsed ductwork. They checked all of it. Nothing is collapsed or pinched, and the ductwork system is sized 10-20% over what is needed for a 2.5-ton system.
* Upstairs dampers closing off in error. We have a very primitive thermostat-based damper system for upstairs vents, and we thought perhaps it was getting stuck shut. Verified that it is open when it's supposed to be, it's responding to our settings correctly -- and in any event the damper will default to open if there were a problem.
* Bad blower motor. The vents still put out plenty of air. You can feel the force 6-12 inches away from the vent. Additionally, Chris asked me to touch the motor once when the system was frozen, to see if it was hot (an indication it's going bad). It was comfortable to the touch.
* Dead transformers, capacitors, etc. I don't even know all of these, but I know my guy has replaced several of these parts just trying to rule stuff out.
* Dirty coil. It's brand new and squeaky clean.
* Dirty filters. They're brand new and clean.
* I might even be leaving something out... honestly, they've checked so much stuff that I can't even keep track of or understand all of it.
**** Aside from the freezing problems, the past 2-3 days I've also had an issue with the outside fan not coming on when cooling is called for. I can hear the outside compressor kick on, and see the fan run for a few seconds or minutes, but then shut off. But the compressor is still running out there. If I let it rest for a while, sometimes it will resume working correctly...?? I do have a low-ambient controller on this new unit, which I understand could shut the fan off when it's cold out -- but it's not cold out. This just happened tonight, and it's only in the upper 60s. Yesterday it happened in the middle of the afternoon, probably 80 out. So, honestly not sure if this is related to the freezing issues, or just coincidental weirdness.
I completely trust Chris, my install contractor. He's been in business for 25 years, solely from recommendations, no advertising. He came personally recommended from several independent sources. But I think he is getting to the point where he's running out of things to check from his experience.
So I just want to know if anyone has any suggestions that might help him know where to look next. ANY ideas would be HUGELY appreciated. I feel so frustrated that we just spent money on a (presumably) good new system, and we're still freezing the unit and struggling to cool the house each day -- when it's barely 75-80 degrees outside so far. Dreading what the summer will bring if we can't figure this out.
HELP! Thanks! :-)