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At this point the only thing knowing the exact charge level (printed on the placard on the unit) would be useful is if the system was pumped down and refilled. Will the new tech do that? Probably not, takes too much time.
There are charging methods other than weighing the charge in. The type of metering device and make of the system determines what methods to use. Some use approach method, some use superheat and some use subcooling. You can use the weigh-in method if you know the exact length of the copper, the size of the copper and how much the factory charge amount to if at all for lineset length. For example Goodman charges the outdoor unit with:
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Adequate refrigerant charge for a matching evaporator and 15 feet lineset is supplied with the condensing unit.
Weighing in the charge is usually done on brand new systems on new homes because the length of the lineset is easily determined by installing technicians as they were the ones to install it. Even then the tech usually would weigh the charge in to get it approximately correct and then the company would send out a service tech to check all operations including airflow, temp. rise, temp. drop across coil, etc. They do that as a baseline because they're going to be providing a warranty period and they want to make sure they're not going to have a bunch of warranty claims because they inadequately installed the system. It used to be the contractor would wait till a really hot day of around 95°F (if it gets that hot) to come out on new installs to verify everything. Now, charging has gotten more accurate and doesn't necessarily require coming back on the hottest and coldest days to verify operation is correctly. The greater use of thermal expansion metering devices has helped tremendously with regard to that.
I can go up to any system and with gauges, temp. probes, temp. clamps, and thermometers along with the large vane anemometer and tell you if the coils are matched correctly, if the piston is the correct size (or if the txv is set correctly and operating correctly), if there are noncondensibles in the system or if there is a restriction in the system.
And the make and model numbers? I was about to attempt to help you know exactly where your HVAC system should be charged.
Your further response is again appreciated.
The AC system is a whole-house central air by Trane, probably 24-ish years old. On the side of the downstairs unit, the part that contains the evaporator, is a small label with Model Number "TXC042B4HPA1" and Manufacture Date "D31" and Test Pressure "300 PSI". (though not relevant the furnace part is "TUS100A948A" if the yellow-highlighting on the "Installer's Guide" left in the basement is correct).
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Here's further information I didn't include in the original post - it's just further info, not necessarily useful, some is based off of short notes I wrote at the time on the side of the furnace (!), other by poor memory:
The original blower motor's bearing(s) failed in July 2001 and the blower motor was replaced by the aforementioned tech with one that was 300-ish RPM slower, top speed.
Apparently I did not notice until August 2006 that something wasn't right. At that time a small notation says "freezing". In September 2007, I personally replaced a horrendous condensation pump PVC drain from the evaporator; vague memories says I saw water leaking directly from the evaporator part and assumed the horrendous original PVC drain work was clogged and THAT was why water was leaking. I also have vague memories of opening up the system and cleaning out foam/etc that I thought was clogging the condensation drain (the original PVC had bends in it, for example, that were almost totally kinked closed, leading me to believe the water leakage was caused by a clogged drain and thus my "fix" for that by properly remaking the PVC drain).
Finally, in May of this year for some unknown reason I decided to replace the blower motor by one that met the original specs of the unit - probably I was thinking about prior years' problems and looked into it online, finding out that low airflow could cause freezing in certain situations (air filters always somewhat clean (*)).
Since then the freezing remains an ongoing problem - I can use the air conditioning cooling for an hour or three, but the airflow noticably declines and, when I turn off the AC leaving the blower running, the water leakage is horrible as the evaporator defrosts. Looking into the problem further online points the finger at low refrigerant level AND the facts that I've related about what the original tech did and the sheer number of years that the problem has existed strongly suggest, IMHO, that this is NOT a problem of a "leak" but instead is indeed caused by the oriignal tech's single-time bleeding off of refrigerant.
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(*) This unit is specced for 16x25x1 air filters but, for whatever reason, filters that fit can be no larger than 15x25x1 (as if whoever made the lowest part of the unit made it an inch too short) - and it's next to impossible to find 15x25x1 filters! So I buy 16x25x1 filters and cut off 1" from the long side. Yes, that's a hack but it works!
The AC system is a whole-house central air by Trane, probably 24-ish years old. On the side of the downstairs unit, the part that contains the evaporator, is a small label with Model Number "TXC042B4HPA1" and Manufacture Date "D31" and Test Pressure "300 PSI". (though not relevant the furnace part is "TUS100A948A" if the yellow-highlighting on the "Installer's Guide" left in the basement is correct).
D31 = 1989 31st week.
I should have made myself more clear. I need the model number of your outdoor unit. But what you provided does bring up some concerns I would have.
First, since you have a cased coil with a furnace, dropping in a fan that doesn't meet specs would cause a higher than wanted temperature rise across your heat exchanger. That's bad.
Second, when you say you looked at the coil to see if it was clean were you able to see the underside of it, the side that's closest to the furnace?
Also, it doesn't necessarily mean that your system is undercharged. It could be that some copper-oxide in the system has broken free and is clogging the metering device. Your filter drier needs to be replaced. The thermostatic expansion valve is sticking.
Do you have something that looks similar this installed on the cased coil?
How about this?
Are you able to see how the coil starts to freeze up? Do sections that are not directly beside each other free up or does the whole coil freeze up universally?
It sounds to me like by it running for 2 - 3 hours before it starts freezing up you have something other than just a low charge.
Excuse me for getting in to so much detail but I'm sort of bored. I stand behind the others in saying you should get a tech but I'm also curious about some of the things you've described.
Excuse me for getting in to so much detail but I'm sort of bored. I stand behind the others in saying you should get a tech but I'm also curious about some of the things you've described.
You may have noticed my posts are rather wordy, too...
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W.r.t. "coil" I opened up a side panel of the air handler and touched various parts of the the radiator-like apparatus inside as the AC was running. At the time I did this the part I've called and will continue to call "evaporator" was very cold near its lower part and essentially room temperature near its upper part. Placing my hand over various parts of this evaporator proved to my satisfaction that airflow was fine everywhere. However. I =was= going to remove a side panel on the evaporator itself to check the blower-side surface but the 479 screws were not conveniently placed (in fact, a couple were placed closely behind tubing) so I decided that, yeah, it probably could stand some cleaning inside there but airflow was good enough that dirt was unlikely the main problem. Since then (but before this message thread) I've given passing thought a couple times about cleaning it anyway just to be thorough.
The unit has a couple panels side-by-side - one covers the evaporator, the other has the entries/exits for the plumbing from/to the outside unit - that panel is narrow and is NOT one I removed to look inside - I suspect the items you asked about are in there but otherwise have no clue about them.
Quote:
It sounds to me like by it running for 2 - 3 hours before it starts freezing up you have something other than just a low charge.
I actually do not know how long after turning on the AC the unit starts freezing up. It could be immediately. However, the airflow remains quite strong (as measured by "face" (!) standing N feet away from an overhead vent as well as little pieces of fluff I've taped to a few vents to watch the flow). For example, last night I "defrosted" the system before bed around 10ishPM, this morning at 05:30-ish there still was noticeable airflow but it also was reduced (fluff at a lesser angle...). Defrosting the unit again at the time increased the airflow and, on going into the basement, resulted in a dramatic flooding all around the air handler...
[pardon late addendum - this problem has existed for at LEAST 7 years, so if it's DIRT it certainly isn't accumulating much]
You may have noticed my posts are rather wordy, too...
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W.r.t. "coil" I opened up a side panel of the air handler and touched various parts of the the radiator-like apparatus inside as the AC was running. At the time I did this the part I've called and will continue to call "evaporator" was very cold near its lower part and essentially room temperature near its upper part. Placing my hand over various parts of this evaporator proved to my satisfaction that airflow was fine everywhere. However. I =was= going to remove a side panel on the evaporator itself to check the blower-side surface but the 479 screws were not conveniently placed (in fact, a couple were placed closely behind tubing) so I decided that, yeah, it probably could stand some cleaning inside there but airflow was good enough that dirt was unlikely the main problem. Since then (but before this message thread) I've given passing thought a couple times about cleaning it anyway just to be thorough.
The unit has a couple panels side-by-side - one covers the evaporator, the other has the entries/exits for the plumbing from/to the outside unit - that panel is narrow and is NOT one I removed to look inside - I suspect the items you asked about are in there but otherwise have no clue about them.
I actually do not know how long after turning on the AC the unit starts freezing up. It could be immediately. However, the airflow remains quite strong (as measured by "face" (!) standing N feet away from an overhead vent as well as little pieces of fluff I've taped to a few vents to watch the flow). For example, last night I "defrosted" the system before bed around 10ishPM, this morning at 05:30-ish there still was noticeable airflow but it also was reduced (fluff at a lesser angle...). Defrosting the unit again at the time increased the airflow and, on going into the basement, resulted in a dramatic flooding all around the air handler...
[pardon late addendum - this problem has existed for at LEAST 7 years, so if it's DIRT it certainly isn't accumulating much]
Here's a quick story.
I had some people who were complaining that there AC wasn't cooling. They were fairly new tenants. I was not directly in charge of this particular property but I got a call from the property manager who was asking for guidance. Her service person had been over there numerous times only to come to the conclusion that nothing was wrong and maybe they were just setting their thermostat too low. His thought process was that as the temperature dropped there was less heat in the air and eventually the evaporating temperatures were dropping below the freezing point and icing up the coil. So I said when I have time I'll come by and check it out. I get there and notice they set the thermostat to 65°F. I asked them if that was the normal setting they keep it at and they replied with "no, but if it's not going to work to get the temperature down then we want it to get as cool as possible."
So I open up the system and notice that the evaporator is caked with dust, hair and debris of other sorts. I took about 45 minutes to clean the coil using a brush and coil cleaner. It looked pretty clean when I got done so I went out and checked the pressures, temperatures, superheat, subcooling, etc. It was way overcharged. I think I pulled something like 5 lbs out of the system (it was a long time ago). Anyways, after a week, I called up the tenant and asked them how it was doing. They said it was definitely working better and it was getting to temperature and cutting off. I told them I'd be by sometime within the next week to check on it. When I got there I opened the system back up and checked the evaporator coil and it once again had a mat of dirt, dust and debris across the face of the coil. I went and got the coil cleaner and the brush and cleaned it again. Went down and checked the pressures, temperatures, superheat, subcooling, etc. It was again over charged so I pulled more refrigerant out of the system (another 1 - 2 lbs I think).
Anyways, the point of the story was that as the coil got more and more clogged whoever serviced the equipment kept thinking it was low on refrigerant so they just kept adding more. What was actually wrong what that because the coil was clogged most of the air was bypassing the coil until it eventually got to a point that it started freezing up no matter how much refrigerant was in the system. The dirt, dust and debris was acting like a shield blocking the airflow from effectively running through the coil. These system at the time were about 25 years old and would now be about 31 years old.
So as you can see it can be a number of things that causes the coil to freeze over, not just low refrigerant like so many want to believe at first. That's why I take caution over believing a older system is low on refrigerant even if the technician previously removed some to adjust for airflow (which by the way doesn't make much sense in terms of how the system runs).
So as you can see it can be a number of things that causes the coil to freeze over, not just low refrigerant like so many want to believe at first.
I understand and have been convinced to eliminate that last variable as the cause of the freezing prior to calling in service - I'll take the evaporator panel off and inspect/clean whatever I find on the blower side of the evaporator (note, however, that I do NOT believe this is the cause because the freezing has been happening for years and, as mentioned, airflow certainly appears to this naive homeowner to be just fine under nonfreezing conditions).
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That's why I take caution over believing a older system is low on refrigerant even if the technician previously removed some to adjust for airflow (which by the way doesn't make much sense in terms of how the system runs).
Now that I've read way too much on the mechanics/physics of air conditioning I, too, have to scratch my head at whatever reasoning was running through the tech's head - INCLUDING why he would install a lower RPM motor when it could present REAL problems with other aspects of the air conditioning heating/cooling.
shop around for R22 if you need it. I was quoted $120 / lb. and wound up finding a guy who topped off my system for $40 / lb.
Yeah, that $120 appears to be well above the range many different web sites suggest is the current going rate.
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