Air Conditioning - Improper AC unit installation?

I recently posted, “AC line size” question but I may have been looking in the wrong direction. I had a unit replaced last year (1.5 ton to 2) from “Nordyne”. The existing line set was 5/8, ¼ and the new unit has ¾, 3/8 lines. The new unit just wasn’t cutting it. The compressor runs constantly when outside temp is around 80-degrees and above and the house temp never gets down to the set temp on the thermostat (set at 75 and the lowest the house temp will get is 77. I was only getting a 12-degree separation. I change the filter every three to four weeks. I was told the line size might be the problem.

Last night the installer came back to check the unit.
1. He said the pressure in the lines was OK
2. The temps between output, 63-degrees (12” above the coil) and intake were 75.
3. He then checked line temp going into the coil which was 49-degrees. He seemed very puzzled as to why there was a 14-degree loss just above the coil. He told me he was going to research this issue and get back to me.

I was given some advice on the problem tonight and I would appreciate some opinions on it.

I was told was that the proper installation of the new unit using the existing line set was to:

1. Flush the lines with nitrogen to clean, especially after any brazing to connect the unit. I don’t think this was done.
2. Install inline filters on both lines. There are none.

In his opinion he feels that the reason there is a 14-degree drop in temp near the coil is that the coil is blocked. This maybe caused by dirt from the old lines and or soot in the lines from brazing connections and may also be building up in my compressor.

I would appreciate any advice I can get to get my unit functioning properly and avoid any possible damage.

wkohler

Which line was 49 degrees? The suction line [the larger one] or the liquid line [the smaller one]? If it's the suction line there is probably some debris in the flow control orifice or the unit is way overcharged. If it's the liquid line, there is a restriction in the piping [like maybe it's kinked somehere?]. It's hard for me to believe that the pressures are normal with that temp reading. Brazing of the lines while flowing nitrogen thru them is the proper way but doesn't always happen in the real world. Have you looked inside the outdoor unit for a liquid line filter drier? The outdoor sections usually come with a filter drier on the liquid line inside the cabinet but not always. On new installs I always use both suction and liquid filter driers; on most jobs I've seen they use a liquid line drier only.

The 49 degree reading is the suction line. I'm not finding any kinks in the liquid line. Is it possible the 1/4" liquid line is to small for my unit.

What should the proper readings be on the gaugages? (BLUE & RED)?


wkohler