OT - What Is A Good Rule Of Thumb For Charging R22 In My Central A/C?

OK, I've gotten a better handle on this (better doesn't mean a whole lot in my case, though).

Here are my stats:

Suction line - 63 psi, line temp is 53.5 deg F Liquid line - 215 psi, line temp is 163 deg F. Ambient air at bottom of condenser is 81 deg. F.

(This is after adding about 2 lbs of R22.)

If I get it, the subcool is now about 15 deg, and the superheat is about 60 deg. But, I don't know how this relates to what I need. How do I figure that out?

BTW, my system is a 5 ton unit, which is oversized for my house, but that's what the idiot installed 11 years ago. I have been told that a

3.5 ton unit would be better for my place. I plan on replacing the whole thing as soon as the money's there; preferably with a ground-source heat pump.

Joe

Not enough information Joe. What type of high side to cold side regulation device does this system have; is is a capillary tube, or thermal expansion valve system?

From your data I would assume capillary tube control, you need to look up the temp. vs pressure tables for R22. You want to shoot for, at minimum thermal load, and saturated suction pressure that is near or above freezing to prevent your evaporator from freezing up. The problem is if that is the operating condition. With this type of "expansion regultor" slightly undercharged systems can freeze the evaporator, overcharged systems will not be cold enough to remove heat quickly. Measure the suction line temperature at the air handling unit, and try to shoot for 38-42 degrees F operating temp. with light load. If it frosts up, add more refrigerant. If too warm, dump some back into your tank. One question would be how low on charge was this, it may have sucked air into the system if too low and as you indicate the leak on the low side, this could be a problem if ANY air has gotten into the system. Along with is water vapor, and this would be a very bad thing if you don't have a dryer installed. ignator

I would stop adding refrigerant here. When outdoor temps get into the upper 90's, the high side pressure will be 250 or higher. That liquid line temp is really high, especially for a relatively new unit. I'd check for dirt in the condenser. I have to wash crud out almost every year with a highly focused water spray, and it makes a huge difference in performance. (I have a pair of 33 year old Bryant ultra-cheapo units that I'm babying along until one blows the big one, which can't be long off.) What is the outlet air temperature from the evaporator?

JOn

Don't know all that much about superheat and saturation temps , but when mine got low from a return line leak (second season of use is when it showed up) I put a clamp-on ampmeter on the compressor lead and charged it until it read rated amps . I did have gauges hooked up , but can't remember now what the exact readings were , but it's run flawlessly now for 8 or 9 years without touching anything but the condensate drain line .

With cars, monitoring the outlet temperature as one adds refrigerant seems to work. Coldest is best.

Spraying water on the condensor is a subsitute for a big fan. A warm day is optimum for trying this shortcut.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Thanks, Jon. The outlet from a register close to the air handler ended up being at 63 deg, with the incoming (room) air at 75. This was in the evening, when things outside were beginning to cool down. Does that seem cool enough?

Eleven YO is a relatively new unit? It's funny how the A/C contractors who come here tell me it's way past its prime. You don't suppose they are possesed by ulterior motives, do you?

I will spray the condenser coils this afternoon; I hadn't thought of that in a while.

Joe

I don't know what type of system I have; I had assumed capillary, but don't know what to look for. Since the suction line was at 63 psi, that translates to about 36 deg F, but what constitutes a "light load"? If the outdoor temp is around 80, is that good enough? Real summer temps here in the South Carolina "mountains" get to be in the low-to-mid 90s on many days.

I may have some air in the system, but I think I'm OK. Anticipating this problem, last fall I shut off the valves in the outside unit to minimize leakage. Yesterday, there was still a little bit of pressure in the lines going up into the attic, so I hope it's alright. There is a dryer installed, as well.

I'll check the line temp at the evaporator as soon as I can.

Thanks for your helpful reply, BTW.

Joe

He was an Extra Terrestrial? Wow! ;-)

No , no , no , he was an Electronics Tech ! Worked at HAFB for something like 26 years in an electronics test eqpt repair shop , forced retirement in '78 due to a broken hip ca 1964 (slipped on a loading dock at Malmstrom AFB). Dad was one of the first people (AFAIK) to be trained to repair CNC machinery for the Air Force . He also worked in Minuteman silo's , and did a lot of other things he never talked about ... he got to ride in some very fast aircraft from time to time , when there was "a problem we need you to look at , Dick" . Dad was one of the most intelligent people I ever knew , and I wish I knew a tenth of what he did ...

You will always miss him. I've lost both family, and close friends over the years. I think of one or more of them several times a week.

As far as ET = Electronics Tech, I try to avoid the confusion by just saying I'm an Electronics Tech, Electronic Engineering Tech, or Broadcast Engineer. In a few months it will be 44 years, including the time I worked as a Broadcast Engineer in the US Army for AFRTS. I tested out of the three year engineering school, and got dumped into a really screwed up radio & TV station in the middle of nowhere. Over the years I worked in almost every area of electronics, including avionics. (A communications system for the ISS, along with the telemetry equipment that tracks the Space Shuttle missions. That was a cool job. :)

BTW, Just think how much smarter he would have been if he was an Extra Terrestrial! ;-)