Looking for Central a/c re-charging details

Many units have a low-pressure cut-out trip switch and/or high pressure cut-out. Under different conditions either may cut your unit off. A charging manifold used to charge with the PROPER refrigerant has a pressure/temperature scale. Each unit has a set charge amount and may vary considerably. Sometimes a unit will have a sight glass in the line and the appearance of "bubbles" will indicate low charge. In cooling mode, the outdoor fan should be blowing hot air to the touch in relation to ambient.

In my area of the country you can't purchase refrigerant without a license.

Do not try to recharge the a/c without proper instruments and knowledge. A quick-check: if there are bubbles behind the condenser, the system might be short on refrigerant.

CAN'T GIVE AN ANSWER ON AMOUNT AS EACH SYSTEM VARIES BY THE LENGTH OF PIPING IT CONTAINS. NEED A GAUGE MANIFOLD AND PRESSURE/TEMPERATURE CHART (THERE SHOULD/MAY BE ONE ON AN INSIDE PANEL ON YOUR UNIT OR IN SOME PAPERWORK INSIDE UNIT). MANUFACTURERS VARY BUT A LOOSE RULE OF THUMB IS MEASURE THE AMBIENT TEMPERATURE, ADD 30 TO IT, LOOK THAT TEMPERATURE UP ON A PRESSURE/TEMPERATURE CHART FOR THE TYPE OF REFRIGERANT (R-22) AND SHOOT FOR THAT PRESSURE AS YOUR HEAD PRESSURE. IT WILL GET YOU CLOSE. SHOULD ALSO BE LOOKING (FOR R-22) AT A SUCTION PRESSURE IN THE 70 PSI RANGE. AGAIN, AS SOMEONE ELSE COMMENTED, IF YOU DON'T KNOW WHAT YOU'RE DOING, YOU CAN DO MORE HARM THAN GOOD. HOPE THIS HELPS

Thanks for the comments so far. My purpose is to observe and compare the numbers that an a/c technicians when they come out to check the system. In the mean time to learn something and also want to know the details, so that to keep the a/c tech. honest.

Another topic, what do you guys think of the ductless split system which was very popular in Asia and Europe? It was advertised refrigerant were pre-charged and the system can be connected easily (DIY type of work).

Thanks!!

I've been interested in the ductless split systems for a long time since seeing them in Japan but they have been very expensive, not available as DIY (which I think they should be) and hardly anyone has sold them. That seems to be changing. I've heard several people say they are very efficient but have never seen any facts to support that. If I had to guess, I'd presume just the opposite. I would guess that the efficiencies come in by only cooling 1-2 rooms instead of the whole house but would expect the smaller units themselves to be less efficient. Because the cost per ton is so much higher than central ducted A/C, they have been mainly useful for locations where running ducts is impractical or very expensive. I have two friends who have them and both of them hate them. Their complaints are that they are too noisy, can't cool adequately and since they are so specialized, maintenance is more expensive than standard A/C units which many people can service.

I'm curious why you are interested in this kind of unit?

Bill

Any a/c system has information, read info from manufacturer to find out how many pounds of Freon is uspposed to have, then, when the tech shows up and test the system or unit, ask how much freon is in it. If you were a DY person, you would need to buy expensive equipment to remove and recharge freon, there are books that teach you basics.

O.K. Here are some other basic things to consider: If the larger (suction line) is cold to touch, and has condensation formed on the outside of it, than the unit probably has a decent charge. This is important for the compressor motor to recieve proper cooling. There aren't many technicians carrying the proper tools to say "how much refrigerant is in a system. This can only generally be done at time of installation, or after a complete recover, vaccuum, recharge. Although there are digital anylizers available, theye are not common tools yet (expensive). Superheat Charging is the most acurate way to test a system charge. Some things have to be noted first: Proper airflow across the indoor coil ! (closed registers, dirty air filter or fan blades, dirty coil from filter neglect.) all very important. Then measure suction line Temp. Where it enters outdoor condensing unit. Compare these numbers using a Temp-Pressure chart for the proper refigerant. A superheat of 12-15 degrees F is standard for most manufacturers.

Mini-splits are great but expensive, for now. If anyone is considering any A/C puchase please request r-410a. It is the common replacement for r-22. R-22 is in the phase-out process in the US and r-410a is the preffered substitute. It has a ODF of 0. (ozone depletion factor). Mini splits are one of the most effeciant cooling means on the market today. The best are the ones that incorperate VFD technology. As the t-stat gets closer to being satisfied, the compressor slows down, the indoor blower slows down, greatly reducing energy usage, while maintaining, and not overshooting comfortable conditions. blah blah blah.

Dan Fritz

HVAC contractor

R-410A operates at almost twice the pressure of R-22. Different gages are required and while you could get by with solder repairs with R-22 -- R-410A requires brazing. The oil used in R-410A is an irritant and a very good solvent. It is important that brazed joints are clean on the inside of the pipe as the oil will carry any contamination to the motor and bearings. R-410A is a refrigerant mixture. Unlike R-22, if you have a leak, repeatedly adding R-410A could result in an imbalance in the refrigerant mix.

R-22 as an HCFC is not available to the general public anymore. After 2020 it will no longer be manufactured as a refrigerant and only reclaimed R-22 will be available for HVAC repair. The more stringent requirements of working with R-410A effectively takes HVAC refrigeration repair out of the do-it-yourself category.

Why are you hiring a tech you don't trust? I don't mind anyone asking a question out of quirosity, but if they don't trust me or are wanting me to teach them what it took me many years to learn I so they can cut me out, I tell them it doesn't say "School" anywhere on the side of me service truck so maybe they should get someone they trust.

Just pressures or a full or partialy filled sight glass don't tell the whole story. If the tech says the system is low on "gas" are you willing to pay to leak check and repair all problems. If not why are you asking. The "gas" went somewhere. You need to have a tight system. This can be expensive because it can be time very consuming to find ALL of the leaks. It's not a needle in a hay stack, it's all of the needles in a hay stack.

There are also other maintenance items that need to be done that affect the performance of a system as much as the refrigerant charge. -- JHF

I'll try to answer your question in a nut shell, If your guages are reading about 70 to 75 degrees on your suction line and about 225 to 250 on your high side your pretty close for r-22 system. Some split systems come with enough refridgerant for about 25 ft. of liquid line and some for about 15 ft. of liquid line check the name plate on the outdoor section it might give an amount of refridgerant that was added at the factory. Once you weigh this amount in if you have 3/8 liquid line you will add .58 ounces per foot of liquid line. If you have 5/16 liquid line it will be .36 ounces per foot and 1/4 liquid line it will be .21 ounces per foot of liquid line. Make sure you pull a deep vacuum and it should hold 30" if you don't have a micron gauge. Do not add any refridgerant without a good vacuum being pulled on the system. Break the vacuum with refridgerant in a gas form and when pressures have equilized turn unit on and adjust charge as needed. You can add liquid into the suction side in small amounts this will speed the process up. That was longer than I thought it would be but I hope it helps.

PSI NOT DEGREE ON THE SUCTION AN HIGH SIDE