How to read a/c charge - what are normal pressures ??

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Bryant Air Conditioner 24000 btu split system - R-22.
I would like to read the charge on this system. I have the manifold gauge set and located the shraeder valve outputs for both sides.
The shraeder valve seems to be tapped off the side of a regular valve... Am I correct in assuming this is the service valve which needs to be opened in order to read the pressure. This might be a dumb question but the valve seems to be closed pretty tightly and I don't want to take a chance on destroying anything. No handle on the valve...so I'm just trying to get a "yes, this is the valve you open" or "No, don't touch that valve..try this approach instead" answer.
So, connect the gauge.... open the valve using a wrench and read appropriate pressures...is this correct ???
Also what pressures should there be ? Someone mentioned a low head pressure of around 200 would be normal while measuring a 20 degree temperature drop at a vent. Also low pressure side should measure about 55 -65.
Can anyone recommend a good online site for home a/c maintenance and repair tutorials ?? All my google searchs have been disappointing.
Thanks in advance.....
Peter
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Peter wrote:

Try asking your question on alt.hvac.
You'll get more replies from the professionals there.
HTH,
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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Yeah, right.
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HeatMan wrote:

The Devil made me do that...
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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You really should be satisfied with measuring the temp drop across the coil. That won't get you hurt either, most likely.
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My properly charged system on a 98 degree day has a head pressure of 310 and a suction pressure of 57.
I found a pdf file on the web that says to charge it with the superheat method and gives charts with superheat specifications.
Sorry but my system doesn't have adjustable valves to isolate the condenser.
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Peter, It's a lot more involved then that. Unless you've been properly trained and practiced with supervision, you run a 99.9% chance of allowing air (a non condensable) into the system just by attaching the gauge set.
If you do some reading, there are numerous things to check without attaching gauges. I'll post some good links for you by tomorrow.
-zero
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Peter
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Here ya go Peter. Instead of a bunch of so-so ones, I found you 1 good one Keep following through the next links at the bottom of the pages:
http://www.longviewweb.com/r22.htm
You may never use that gauge set, but that's ok. After some good reading you'll be more astute to weed through the service techs till you get a competent one.
-zero
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What's the point if you're not licensed to buy refrigerant anyway?
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wrote:

Several things on my mind...... I had several techs look at the problem (paid for several opinions). This is on a system in operation for about 12 years....seemed to be working fine and then blew a breaker one day.
First team of techs said it was leaking "like a sieve" from the flare coupling by the metering valve. When they checked the freon, it was only a little low. So one would think "leaking like a sieve" means freon should be pretty low. But they quoted 375 head pressure and 55 low pressurre. Estimated cost to repair leak and clean both coils was 650 - to 850 dollars.
Second tech comes in, measures charge, looks at leak (doesn't use a sniffer) and says "you have a leak, you're a little low on freon.....I will overcharge the system a little to so it will work until you have a chance to talk to our salesperson.". He estimated 1200. to correct the leak, another $500 to clean the evaporator coil. Total of $1800. Clear message "Buy a new system" He was very technically correct in saying.."overcharging will kill the compressor" and " you will have water damage on floor" (low freon will cause evap coil to freeze).
Another tech suggested using a can of HVAC-R stop leak.
Three weeks later, system is still cooling fine. I am looking to verify loss of freon. One way or another, it's important to get this situation resolved.
With a new Bryant A/C running anywhere from 5 to 10 K (actual quotes)....... it would be important to me to see exactly how much of a leak is there and IF it can be stopped by a can of HVAC-R sealer which was recently recommended. Also knowing how much of a charge remains would be helpful to be able to discuss "solutions" intelligently. Do I have 6 months to replace the system or 6 days. Also, did cleaning the coils actually make a major difference in operating efficiency.
The members on this forum are a fantastic source of information and guidence making it easier to become "knowledgeable" to solve minor problems, perform routine maintenance maintenance and to make intelligent choics"
Peter
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When a unit blows the breaker, the very first thing to do is look at cleaning the outdoor unit. If the behavior continues, the next step is to measure the amp draw of the motor. If this is well within spec, the breaker may need to be replaced, it is not rare for them to become weak with age. Some units benefit greatly by a bit of shade on the outdoor unit. When temperatures are out of control I would not recommend spraying water on the coil as the mineral build up will exceed the limited benefit, though it is often done.
Have you been adding Freon on a regular basis? A 20^ drop between supply and return would be as good as you would ever do. It will not be as much as the ambient goes up and can be as little as 10 or 12. If the large diameter line entering your outdoor unit is sweating or very cold, you are probably fine. The small diameter line should be very hot to the touch. Make sure that the filter is clean to allow sufficient air to move across the coil. There should be an access door of some type at the A-coil that would let you inspect the cleanliness of the coils.
You can test for a physical leak by squirting soapy water on the fittings. Lava soap made into a liquid makes a great leak detector. Unless the leak is substantial, it will be very hard to see with a gauge set. The pressure numbers change continually with temperature, etc. On a good hot day, I like the R22 scale to read about 45. There is certainly more science involved than this. The pressure you read is not like reading air pressure on a tire gauge.
Residential split systems are meant to be 15 year systems. There are many that go longer, but increased SEER ratings and motor efficiencies would indicate to consider replacement. ______________________________ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net
wrote:

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Cleaned both condensor and evaporator units. The breaker never tripped again. It's been several weeks now.
I'll check the motor draw. (just because it's a nice thing to do)

No, with the exception of the service call two weeks ago who added freon to top the system off, we haven't added anything for about 8 years.
Large is cold, small is hot. It seems that the top of the compressor is hot to the touch.... I ordered a thermometer so to get some accurate temperature reading. The laser ones looked tempting but I settled for a less expensive one.

shape. I used the coil cleaning spray which penetrates the fins and used a hose to rinse out the residue.

System has run trouble free up till now.... which makes it difficult to determine whether it's repairable and will last for another 5 or so years, If it was a problem child the decision would be easier. But so far it's been solid as a rock, until now when it blew a breaker. (btw, I'm working on this for a friend who has no idea about maintenance. The coils have never been cleaned and no one ever told her about replacing the filter either. She had a service contract for years but stopped it recently.... I guess they never replaced the filter either.
Any idea of how much it would cost to replace the system ???
Your input and advice is very much appreciated !! Every little bit of good advice helps !!!
Thanks again !!
Peter

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Cleaned both condensor and evaporator units. The breaker never tripped again. It's been several weeks now. CY: Might be time to just leave it, and keep using it. Could be about as fixed as you'll get.
I'll check the motor draw. (just because it's a nice thing to do) CY: Should be a name plate and the run amperage should be on the plate.

No, with the exception of the service call two weeks ago who added freon to top the system off, we haven't added anything for about 8 years. CY: That's good news.
Large is cold, small is hot. It seems that the top of the compressor is hot to the touch.... I ordered a thermometer so to get some accurate temperature reading. The laser ones looked tempting but I settled for a less expensive one. CY: Normal for the compressor to be hot. Harbor Freight has infared thermometers cheap enough. I got a couple of them that are keyring size, for six bucks each. No laser aimer.

shape. I used the coil cleaning spray which penetrates the fins and used a hose to rinse out the residue. CY: Way to go.

System has run trouble free up till now.... which makes it difficult to determine whether it's repairable and will last for another 5 or so years, If it was a problem child the decision would be easier. But so far it's been solid as a rock, until now when it blew a breaker. CY: Probably dirty coils.
(btw, I'm working on this for a friend who has no idea about maintenance. The coils have never been cleaned and no one ever told her about replacing the filter either. She had a service contract for years but stopped it recently.... I guess they never replaced the filter either. CY: With that kind of service contract, sh eprobably needs her coils cleaned, also.
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Several things on my mind...... I had several techs look at the problem (paid for several opinions). This is on a system in operation for about 12 years....seemed to be working fine and then blew a breaker one day. CY: Blown breakers, any of several reasons.
First team of techs said it was leaking "like a sieve" from the flare coupling by the metering valve. When they checked the freon, it was only a little low. So one would think "leaking like a sieve" means freon should be pretty low. CY: yes, you'd think so.
But they quoted 375 head pressure and 55 low pressurre. CY: We don't know what the temperatures were at the time he checked, or if he told you the truth. But, if we make some WAG, here, the freon may be a bit low, and the outdoor unit is in desperate need of cleaning.
Estimated cost to repair leak and clean both coils was 650 - to 850 dollars. CY: How much to just clean the outdoor unit?
Second tech comes in, measures charge, looks at leak (doesn't use a sniffer) and says "you have a leak, you're a little low on freon.....I will overcharge the system a little to so it will work until you have a chance to talk to our salesperson.". He estimated 1200. to correct the leak, another $500 to clean the evaporator coil. Total of $1800. Clear message "Buy a new system" He was very technically correct in saying.."overcharging will kill the compressor" and " you will have water damage on floor" (low freon will cause evap coil to freeze). CY: Sounds like he's pushing a new system.
Another tech suggested using a can of HVAC-R stop leak.
Three weeks later, system is still cooling fine. I am looking to verify loss of freon. One way or another, it's important to get this situation resolved. CY: I can undersand you wanting to get some real answers. Sounds like every time you get another estimate, you get two more answers.
With a new Bryant A/C running anywhere from 5 to 10 K (actual quotes)....... it would be important to me to see exactly how much of a leak is there and IF it can be stopped by a can of HVAC-R sealer which was recently recommended. Also knowing how much of a charge remains would be helpful to be able to discuss "solutions" intelligently. Do I have 6 months to replace the system or 6 days. Also, did cleaning the coils actually make a major difference in operating efficiency. CY: Yep, it sure is nice to be able to have some time to work. Dirty coils really kill the efficiency of a unit. Did it help yours, to have em cleaned? Depends how dirty, and how good was the cleaning they did.
The members on this forum are a fantastic source of information and guidence making it easier to become "knowledgeable" to solve minor problems, perform routine maintenance maintenance and to make intelligent choics" CY: I've really learned a lot on alt home repair.
Peter
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Sorry for not responding sooner... life suddenly became busy from several different directions.

It was an indication to start looking into the cause. Lots of helpful suggestions came in from this group and also from the diagnosis's of the technicians i.e. coil cleaning. There was a lot of help from the group in checking out the electrical part. And for suggesting ways to clean the coils. Plus measuring temperature drops across the coils and on the vapor and liquid lines.

many parts of the system as possible before giving an informed opinion. Still need to map out temp's on different parts of the system and check motor draw. Blowers are kinda noisy...so I need to check if these motors bearing require oiling.

Didn't get a separate quote for the outside unit, but this unit is through the wall and is located about 16 feet off the ground. There is a condominium hose spigot about 30 feet away. Plus the outside coil unit cover was painted in place by an excellent maintenance crew. So unless the tech was really motivated to do a good job......this would have been either a problem area or the job would have been more costly and time consuming than estimated.

His agenda was full of imminent doom which set off alarm bells. Part of the fault was mine, because I don't know enough about a/c systems to determine how truthful he was. So far he seemed to be pretty knowledgeable, except that his final solution " replace system immediately" might not be the only option available. Time will tell.

Thanks to the advice of this group, I located some coil cleaners online and cleaned coils myself. They started off caked with dirt and finished looking pretty new. Took my time, followed the advice of this group, didn't do any damage and with a little persistence the coils came clean.
It would be nice to have a method to verify how more effective the system was after the cleaning

Agreed.... this group is like having an expert at your side I enjoy returning the favor by providing advice where I'm qualified and have the knowledge to do so. Makes it fun to do home maintenance and upgrades. Guess we all enjoy working on stuff.
So how much more do I have to know before you tell me how to use the manifold gauge set ????

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Bryant Air Conditioner 24000 btu split system - R-22.
I would like to read the charge on this system. CY: Why? Supposing you do get some pressures. What will you do with the information?
I have the manifold gauge set and located the shraeder valve outputs for both sides. CY: I own a couple scalpels, and some gauze. And some sutures. But that doesn't mean I should go cutting into people.
The shraeder valve seems to be tapped off the side of a regular valve... Am I correct in assuming this is the service valve which needs to be opened in order to read the pressure. CY: Actually, no.
This might be a dumb question but the valve seems to be closed pretty tightly and I don't want to take a chance on destroying anything. No handle on the valve...so I'm just trying to get a "yes, this is the valve you open" or "No, don't touch that valve..try this approach instead" answer. CY: No, don't touch that valve. Don't have to touch the valve to read the pressures.
So, connect the gauge.... open the valve using a wrench and read appropriate pressures...is this correct ??? CY: Not correct.
Also what pressures should there be ? Someone mentioned a low head pressure of around 200 would be normal while measuring a 20 degree temperature drop at a vent. Also low pressure side should measure about 55 -65. CY: That depends on the indoor and outdoor temperatures, and also depends if the coils are clean or dirty. Also depends on air flow through the coils. Do you know which valve allows you to read the head pressure? And which hose goes to which fitting? You mention two fittings on the AC. But your gages very likely have three hoses. Blue, yellow, and red. Were you able to find the third fitting on the AC system?
Can anyone recommend a good online site for home a/c maintenance and repair tutorials ?? All my google searchs have been disappointing. CY: Don't know of any.
Thanks in advance..... CY: I'm guessing you are an engineer?
Peter
CY: At the moment, it sounds like you have a real curiosity. But there are some things which are dangerous, and this is one of those. Yes, it is possible to hurt yourself by not knowing what you're doing with a set of gages.
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Stormin Mormon wrote:

I know I will get flamed for this by the pros, but whatever....
If your system has the correct charge then the evap coil will be cold for its full length but somewhere along the return pipe to the compressor it will start to feel warmer indicting all the freon liquid has evaporated and only vapor is returning to the compressor.
If the system is overcharged, the return pipe will be cold all the way back to the compressor and liquid freon may be entering the comp which is not really a good thing.
If the system is low on charge, then only a portion of the evap oil will be cold, the portion nearest the expansion valve.
In short, with the correct charge, the full evap coil is cold, but not the retun pipe.
This is obviously a guideline. Also, if you don't know what I mean by evap coil or expansion valve then you need to do a bit more studying.
Mark
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Thanks !! I have a somewhat accurate laser thermometer coming in this week (hopefully)...at which point accurate measurements will be taken throughout the system. This guideline sounds like a good starting place.
Regarding the book... I've been working my way through John Tomczyk's "Troubleshooting and Repairing Modern Air Conditioning Systems). It's been pretty informative.and has good information, but the advice that has been coming from the members on this forum has been priceless in helping me understand what to look for and also finding information on the net.
Thanks again for your help !!
Peter
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This is of course not correct. The suction line should be cold all the way back to the condensing unit. the only way to correctly check is by taking a superheat reading.
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