Hi all. I am trying to figure out if my HVAC company is a bunch of idiots or if I just misunderstand subcooling.
For my small Baltimore rowhouse I just got a newly installed 2 ton, 16 SEER split Carrier central air conditioning system that uses R-410A (cost me $x, ductwork was already present). I am worried the techs who installed it did not charge it enough. It has TVX valves so you need to use subcooling to measure the charge.
They recorded a 245 psi Head pressure and 115 suction pressure on my installation receipt. He also wrote "10 degrees subcool" on the receipt, which I don't see how that is possible when a 245 psi equals 83 degrees on an R-410a P/T chart.
The small, copper liquid line (when measured near the compressor valve) doesn't seem to heat up much at all (does not feel warm to the touch). When I measure it with a thermometer I get temps a few degrees above ambient. Once I measured it at 95 when it was 90 outside. A second time, I measured the liquid line at 87 degrees when the outside ambient temp was 83.
Does it sound like I'm low on refrigerant?
Is a 245 psig pressure just flat out too low for any system?...it seems it would be impossible to get 10 degrees of subcooling at that pressure since it is equal to 83 degrees... to get the 10 degrees of subcooling your liquid line would have to be like 73, which would be colder than ambient (isn't the liquid line supposed to be warm/hot?).
The system actually cools ok with a healthy temperature split approaching 20 degrees. My concern is the system is not working as efficiently as it could and/or is being subject to excessive wear and tear due to a low charge.
Oh, I don't want to make this post too long but on the inside of my compressor's service panel there is a chart used for measuring subcooling that I don't fully understand. Here is a recreation of that chart:
------Required Subcooling Temp------
Pres | 6 ,| 8 ,| 10 | 12 | 14 | 16
251 | 78 | 76 | 74 | 72 | 70 | 68
259 | 80 | 78 | 76 | 74 | 72 | 70
266 | 82 | 80 | 78 | 76 | 74 | 72
274 | 84 | 82 | 80 | 78 | 76 | 74
Since this chart provides pressures from 251 - 274, does that mean my pressure should fall within that range?
Thanks alot for any advice! I've been browsing this site for awhile and it's been great for learning.