I have a split AC system. The evaporator is in the attic.
About a year ago the AC stopped cooling. Called a HVAC company, they came
tested the freon pressure, no freon. Looked for leaks - none found. Charged the
system and left. Everything worked OK for the remainder of the Summer. Comes
April this year, I turned the cooling on, no cold air. Called the same company,
no freon again. I insisted to have the system checked for leaks – the guy puts
in about 2 lbs freon - inspects the system for leaks: no leaks. I told that I
would not allow him to fill the system again and have it empty few weeks later.
He leaves and promise to send back a more “experienced guy”. In the meanwhile,
I made a soapy solution and went around looking for bubbles, sure enough a find
a good leakage near one of the Schrader valves by the compressor. A couple of
days later, a second guy from the same company shows up. I ask him to confirm
the leak I found and he does it – tighten the screw, the leak stops. Then he
recovers the leftover freon, vacuums the system and after that starts putting
in new freon. I tell him that from last
year repair from his company, the system capacity is about 7 lbs. After a short
time while he is pumping in freon, the suction line freezes. He starts to go
around looking for “blockages”. Removes the flexible pipes from the dampers in
the attic, measure flow from the register, and confirms that I have a blockage.
However, he has an appointment somewhere else so he will return the next day.
While all of this was going on, I noticed that he had pumped in about 11 lbs of
freon into the system. I make him aware of that and he tells me that while I was
not around he had recovered “all the excess freon”.

The next day, I am expecting the guy or someone else from the
company to show up to finish the job. After I realize that no one is going to
come, I call the company and I am promised that someone will certainly show up
to complete the work. No one ever comes. In the meanwhile, the system is
running but with very little cooling, and in addition when the compressor
starts it makes a strange rattling noise that would transmit through the lines
inside the walls. After several weeks of poor AC performance I call a different
company. The tech confirms my suspicion, the system is overcharged with freon.
He removes about 2 lbs and measures various parameters afterwards, which I summarize
below:

Pressure suction line = 76 psi (48 oF)

Temperature of suction pipe = 62 F

Superheat = 14 F

Compressor draw ca 21 amp

Delta T in the attic 17-18 F (78.1 F air in – 60.5 F out the
evaporator)

After the service the system performance improved a lot,
until that is, the real heat and humid weather, typical of late June here in
the Midsouth, kicks in. Now, with temperatures running in the high 90s, the
system struggles most of the afternoon (we have it set at 85 during the day) to
manage to bring the temperature down to 79 F (thermostat setting for the
evening) in the upstairs floor, which eventually reaches after 7-8 hours of continuous
running. It does reach the set temperature downstairs much sooner (thermostat
there set also at 79 F) because the downstairs is obviously a lot cooler to
start with.

Recently, I measured the delta temperature in the attic and
found to be about what the pro guy found, about 18 F differential (62 F outflow
and 80 F inflow) measured at the evaporator box.

What I do not understand however, is why the temperature
measured at the registers both upstairs and downstairs reads about 80-81 F not
the expect much lower 62 F measured at the evaporator coil box.

Does this mean that I have a leak in the attic ducts (temperature
there is over 100 F) or something else? I also tested the dampers in the attic
(two zone system) and both open and close appropriately.

I would appreciate any suggestions.

Thank you