Check out some similar questions!

jomap · Jul 7, 2013, 12:06 AM

Bought a house with ac unit not working. Paid to have it charged up. It leaked and was nonfunctional in four days (couple hundred bucks). Decided to use nitrogen to pump it up and find the leak myself. Found it and fixed it! Now I'm all set up with a set of gauges and a tank of R410A to charge it up myself this time (less than a couple hundred bucks). I plan to release the remaining nitrogen prior to charging the system. But I'm not sure what I'm looking for while charging it up. I don't want to overcharge or undercharge. The only info on the data plate which looks like it might be important is "HFC 410A 7 lb 15 oz" and "design psi high and low 480". Should I add r410a (in small doses as I have read) until the high and low side are at 480? I have temperature probes I can use also. What should I be looking for to find the sweet spot for my AC unit? Thanks

Joshdta · Jul 7, 2013, 07:14 AM

Ac units should only be charged by a licensed contractor. That being said on a typical 80 degree day the suction side should be running around 135 psi

jomap · Jul 7, 2013, 07:45 AM

Hi Josh, Wish I lived where the summer had "typical" 80 degree days. I'd probably sell my ac unit. So if I'm in East Texas where the typical summer days almost always hit 90, frequently hit mid and upper 90's, and sometimes 100, will it make much of a difference on the 135psi suction pressure you mentioned? Is the suction pressure THE number to watch so that when I get there, I know it's correctly charged?

ma0641 · Jul 7, 2013, 09:10 AM

410A? How are you going to evacuate the system? A set of gauges and a tank of 401A only pressurizes.

jomap · Jul 7, 2013, 09:55 AM

Leak was from a zirc fitting which had a cap on it. So it's not as if the system was open to atmosphere to get air in it. It simply pressured down and sat there. Plus it has had a couple pump and dumps with the 410a charge (which leaked out in 4 days) and the little bit of nitrogen I used for leak finding, some of which is still in the system and will be bled off.

ma0641 · Jul 7, 2013, 11:24 AM

Even bleeding off N2 to STP, will still keep an equilibrium of N2 and 410A Freon before recharge. Not using a vacuum pump will still keep some N2 in the system and it will not become liquid, just like keeping air in it. Will it run, yes, but not at 100%. I would try to borrow a Vac pump .

mygirlsdad77 · Jul 7, 2013, 02:33 PM

Good to see you back, Joshdta.

jomap, this really is a job for a refrigerants licensed tech that knows how to do the charging properly. If the line set is right at 25 ft long, you can simply vacuum the system and add the factory charge by weight (a good refrigerants scale and vacuum pump is going to cost you more than a tech at this point, promise). If you get the charge wrong, you will have nothing but problems with the system, it will even effect the indoor unit blower when the a/c system freezes up. Hey, Im not trying to be a spoil sport, you can give er a go if you want, just know that you may end up doing more damage than good. There really is a reason we need to be licensed and insured, and knowledgeable when it comes to our trade to do this type of work. I realize the bill hurts when the work is done (especially when the job isn't finished correctly, maybe call another company to do the recharge?) But that is the price of being cool sometimes.

Wishing you the best of luck on this.

Stay cool.

jomap · Jul 8, 2013, 10:45 AM

Hi, Thx for the info. I won't be calling the ac guys especially when my instincts tell me the loose zirc valve may have been left by them. I wonder how much they would have charged to come out again and find the loose zirc valve. Then there's still the charge for refilling the system. What a racket.
When I described to him the history, he simply refilled, but didn't evacuate. He decided (and I agreed) that it had simply been sitting there and wasn't opened to atomosphere. Here's the history. In 2008 when I bought the house the ac was working on the day I bought the house. It may have had a leak at that time and they simply charged it up to get it through the sale. Then it sat there until spring of last year (but I did run it a couple minutes a couple times each year while it was inoperative). The ac guy charged it up (I think he billed me for 3# r410) and it worked good for 2 days, then by the day 3 and 4 I knew the charge was leaking. I didn't do anything until this year. I decided to put in some nitrogen and go to work looking for the leak. I started the leak search at the two fittings coming into and out of the compressor unit since I still had a hose connected from adding nitrogen. One of them had a significant leak... about 3 bubbles into a bucket of water each second. I decided that may be the entire leak problem and didn't have to spray any soapy water from a spray bottle to find the problem. I tweaked the valve a bit tighter and quit looking for leaks. That was it. I really wonder if the AC guy put it there. It's right where he was working. I don't remember if he added refrigerant to the suction or discharge. But he was right there and I wasn't watching him the whole time. There's just a little bit of nitrogen pressure on the system and it has been sitting there for a couple of months now, so I'm confident that was the leak. I know the nitrogen is much lighter than the r410. So I will bleed from a high point at the zirc valve which is about 7 feet in the air at the evaporator. Even if I have to do several charges to get it right, it's still cheaper than the one time charge which lasted only a couple of days. And I can do it again next time if I need to. Seems to me that getting a charge, having it leak, calling for service to find the leak, then getting it charged again would be a significant chunk of buying a new unit and I don't need to do that. It gets real expensive real fast and I'm at their mercy. They can run circles around me with their knowledge of the system (loose zirc valve was an easy one to put in and an easy one to fix, probably wouldn't have been cheap to pay them to "find" it). I'm not going to let the ac mafia around here get into me any deeper than they already have. I've been a do-it-yourselfer all my life. I can do this too, but I just need to find the correct information. I can probably find a cheap, functional vac pump at Harbor Freight. Getting the system evacuated isn't a big deal. But once it's just sitting there I'm wondering what temperatures or pressures (or temp or pressure differences) I should be watching. I was peppering the ac guy with questions. I do remember him saying something about the temperature difference between the air into and out of the evaporator (was it 40 degrees delta is good?). I think I remember seeing it in writing that a delta t of 20 to 35 degrees on the suction and outlet of the compressor indicates a good condenser function. I have worked with pressurized systems in reactor plants, refinery, and gas pipeline, so that part of this job doesn't worry me. Also have solid electrical/electronic background. I'll start with a clean condenser coils and a clean air filter and just need to find some numbers to watch for in regard to temp, press, and delta t and delta p. Josh gave me a number to watch for on suction press and there's probably a few more to watch for. If I get that info, I can do this. Is the number I found on the data plate (7 lbs. 15 ozs) the factory charge? Also, for info, I observed no oil residue at the leak sight. So the ac guy and I decided it probably didn't need oil. I'll evacuate at the high point to minimize pulling out any oil. It also doesn't sound like a machine in need of oil when it's running. Thanks for your help

QUOTE=mygirlsdad77;3500967]Good to see you back, Joshdta.

jomap, this really is a job for a refrigerants licensed tech that knows how to do the charging properly. If the line set is right at 25 ft long, you can simply vacuum the system and add the factory charge by weight (a good refrigerants scale and vacuum pump is going to cost you more than a tech at this point, promise). If you get the charge wrong, you will have nothing but problems with the system, it will even effect the indoor unit blower when the a/c system freezes up. Hey, Im not trying to be a spoil sport, you can give er a go if you want, just know that you may end up doing more damage than good. There really is a reason we need to be licensed and insured, and knowledgeable when it comes to our trade to do this type of work. I realize the bill hurts when the work is done (especially when the job isn't finished correctly, maybe call another company to do the recharge?) But that is the price of being cool sometimes.

Wishing you the best of luck on this.

Stay cool.[/QUOTE]