Maybe some of you salty techs could offer some pointers for a lowly rookie.
Last night, boss gives me a "special project." Basically, the deal is, he allots X dollars to sort of MacGyver a system for a stingy house flipper. The less I spend in materials, the more money he gives me.
Anyway, the customer's trying to sell this remodled house, but the AC's *not functioning properly*. HIS complaint is clear: the AC's not bringing the temp down QUICK enough, so MY mission is equally clear: To get the MAX temp split out of the system, while spending MIN dollars to do so (not even concerned with humidity).
So, boss sends me to house armed with only a thermometer, gauges, and jug of refer (a dangerous combination in the hands of a rookie). The original system was installed abt 10 yrs ago by a very reputable company in our area. The AC and coil appear very clean, but I observe the following anomalies:
1. AC unit is 2 ton 10 SEER, but furnace is 100,000 with 4 ton drive (house is only about 1400 sq ft, med insulation, 9 runs (presumably 6")--IMO, undersized AC, oversized furnace for Indiana climate.
2. The mother board on furnace had been replaced (by original company), and heat, cool, & cont blower speeds were all jumped to high. In spite of this, some registers seemed weak, and none really had the "jet" feel one would expect under those circumstances.
3. The liquid line was 5/16, but the unit was clearly stubbed for 3/8.
4. Probably doesn't matter, but the T-Stat was pretty far from the return (15 ft).
5. Going into the A coil, about 2 ft of the suction line was bare and exposed.
Here was the initial performance of the system when I got there. Ambient and indoor were both low 80's. Started up unit, temperatures in registers were only 3 degrees colder than indoor temp. Went outside, suction & liquid line were both *luke warm*. Put gauges on unit, suction pressure was about 45, but the schrader on the liquid line was blocked, and I didn't have any extracting tool on me. Despite knowing better, temptation got the best of me, and I started slowly adding refer and observing the temp split. But here's where it gets wierd.
I got the suction up to about 80, and the temp split was now about 11 degrees, but for some unearthly reason, the suction line was COLD. My thermometer was inadequate for the task, but I'm guessing my superheat must have been damned near zero. The liquid line felt luke warm at best, so I'm guessing my subcooling was high. It was like I had overcharged the system. But I had been watching the temp split slowly rise from 3 to 11 as I slowly added charge, so I couldn't really understand how I managed to overcharge it.
I was thinking, if I were truly getting 1600 cfms (from the 4 ton drive at high speed), which I almost certainly wasn't (higher than normal for a 2 ton, but probably not THAT high--my guess would be 1300 actual), I might expect an optimal split on a 2 tonner to be in the 10 degree ballpark, maybe more since the sensible/latent ratio would go up.
Also, I was thinking that those conditions (undersized liquid line, excessive airflow, exposed suction line, etc) would give me relatively HIGH superheat at a relatively HIGH suction pressure, even though the measured conditions seemed to be backasswards.
So, I decided to let the unit run a while, went home, ate a hamburger. Came back to the job, and saw that after about an hour running time, the unit had dropped the indoor temp about 7 degrees. Normally I wouldn't guess this is too bad, but I imagine the ambient had dropped a bit too. Went back home, decided I'd sleep on it, and try again this evening (lost a lot of sleep, as these things tend to bug me).
Thus, my question: Does anyone here have any tips on what kind of tools I should take, or what kind of tests I should do? Since this is a special "after hours" project, I'm free to lollygag at my own pace (really love this kind of scenerio, btw). My only limitations are expense. Also, does anyone here know how sensitive sensible/latent ratios are to high cfms? The only data I have are on 350 to 450 cfms per ton, and not on gross overkills. My hunch is that ductwork issues may be at the heart of the problem.
Any help would be greatly appreciated.