I have two identical 4 ton units, 1 upstairs and 1 downstairs. The downstairs unit runs like a champ, however, the upstairs unit hisses at the evaporator. The house is new (3 years old) and have had the AC company that installed it take a look at it several times. It is an intermittent problem, and seems like every time they come out it runs quiet. In March the compressor died, and was replaced. I still have the problem, however, the hissing has become louder and the compressor will shut off violently (I hear a thud as if the pressure was way too high.) The only other clue to the problem is that it hisses all the time but tends to get louder in the afternoon and peaks in terms of "loudness" around dusk (if it occurs.)
I can see myself having to replace the compressor again if the problem is not rectified. Any ideas what this could be? I need some advice on how to direct these repair guys, or at least be armed with some knowledge when I shop around for a new AC repair company.
Thanks,
Will