Subcooling seems to be a great mystery to a lot of service techs in the field yet, any unit with a TXV type metering device, should be charged by subcooling instead of superheat. Since a TXV has a pre-set superheat (or an adjustable superheat) setting, it will always try to maintain that superheat even if the unit is over or under charged. This is why charging by subcooling is important for units equipped with TXV’s. Let’s review the process of subcooling first, and then see how to charge by subcooling. The compressor puts out HOT HIGH PRESSURE VAPOR as part of the compression process. This vapor enters the condenser coil, which performs the function its name states, to turn the vapor into a liquid. As the vapor travels through the condenser, heat is removed and the vapor starts to turn to liquid. At some point in the coil, the vapor has been turned to all liquid. This is called saturated liquid and corresponds to the temperature and pressure you read on your gauges. This usually occurs before all the passes in the coil have been used.

These extra passes through the coil take the saturated liquid and removes even more heat, or, subcools the refrigerant. This is important, since a metering device must have a continuous column of liquid to operate properly. By subcooling the liquid before it leaves the condenser, we “guarantee” that the liquid will remain liquid all the way to the TXV. If there is insufficient subcooling, the liquid can turn back to a gas (flash gas) and the metering device will not properly meter the refrigerant into the coil.car air conditioning repairs randburg Now that we understand how subcooling is suppose to work, we can now proceed with how to charge by subcooling. 2004 nissan titan ac control unitAs stated earlier, when your gauge set is attached to the unit, the “head” or liquid pressure you read is the saturated liquid temperature/pressure. daikin ac units uk

Knowing this, and the manufacturer’s recommended subcooling, you can properly charge the unit. You need to strap a thermometer or thermocouple to the liquid line out side the condenser so you can read its temperature and then add or remove charge to get the desired subcooling for that unit. Let’s look at an example. If you had a “head pressure” of 198 PSIG and looked at a temperature/pressure chart, you would see that the saturated temperature is 100 degrees. If the unit required 10 degrees of subcooling, the thermocouple attached to the liquid line should read 90 degrees (10 degrees “colder” than saturated temperature). Let’s say the thermocouple reads 101 degrees. Do I add or remove refrigerant to get the 90 degrees temperature I need? The key to answering this is to remember that the closer to ZERO or temperatures above the saturated temperature, indicates an undercharge. Think of it this way, since the unit is short of refrigerant, the discharge temperature of the compressor increases because there isn’t sufficient cooling of the compressor.

Since the discharge temperature is higher, it will require more of the condenser coil to remove the heat of compression, which causes little or no subcooling. So, we need to add refrigerant to cool the compressor to lower the discharge temperature to get our desired subcooling. Conversely, if the liquid line were 80 degrees, this would be 20 degrees of subcooling, which is an overcharge. The compressor is cold, the discharge temperature is down, the condenser does not have to remove as much heat, so the refrigerant reaches saturated temperature quicker leaving more coil passes for subcooilng. In order to get the 10 degrees desired subcooling, we would need to recover refrigerant to raise the compressor discharge temperature to require more of the condenser to be used to reach saturated temperature leaving us with the proper amount of passes to subcool the saturated liquid. If you keep this in mind, properly charging a unit by subcooling will become very easy. How did yesterday's political debate affect your opinions of the two presidential candidates?

Have you or someone you know well been affected in the recent years about the rising costs of an EpiPen? What do you think will be the long-term effects of the new U.S. military aid deal with Israel? How do you teach children who weren't alive for 9/11/2001 the importance of the changes of these attacks? What is your opinion of the purchase of Yahoo for $4.8 Billion by Verizon? no, I think lb (pound) is a unit of mass (sometimes called weight) and psi (pounds per square inch), so if you get lbs/in2 (Inch square I mean) it's same like psi, or lbs/in2=psi no, I think lb (pound) is a unit of mass (sometimes called weight) and psi (pounds per square inch), so if you get lbs/in2 (Inch square I mean) it's same like psi, or lbs/in2=psi I am thinking this is the closest to the real scenario. Pounds is a unit of mass and PSI is also a unit of mass (it measures how much of something is IN something else) so the lbs/in2 would work to do this conversion Posts: 25Joined: Tue Jul 31, 2012 1:24 am

Return to How to convert? Users browsing this forum: No registered users and 6 guestsThe requested URL /showthread.php?t=51526 was not found on this server. Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.In our third article, we take a closer look at some provocative questions raised in recent press coverage.  We thought a good jumping-off point was a recent New York Times article on residential air conditioning; below we address a few of the nearly 100 reader comments (in italics below) submitted in response to the article.By Jill Abelson and Jeff CohenChlorodifluoromethane, better known as HCFC-22 or R-22 is a common refrigerant that is currently being phased out in the U.S. due to its very high potential to exacerbate ozone-depletion (R-22 is also a global warming gas). U.S. EPA has tried to reduce use of this material by imposing strict quotas on its production. Since 2010, the agency has also banned sale of new air-conditioning units containing the compound, and has promoted recycling of the gas from old machines so it will not be released.

Despite these efforts, the agency has drawn criticism for not doing enough. Can a bounty or buy-back program help?  What about a cap-and-trade program?Let’s first look at some of the things related to R-22 that are legal and are not legal:Without a doubt, there are challenges in enforcing these and other regulations for R-22 and other refrigerants. High visibility enforcement actions have been effective. Ultimately, the best way to guarantee proper management and minimize/eliminate emissions is to offer economic incentives for equipment owners, technicians, distributors, reclaimers, metals recyclers, and other participants in the “value chain.”A cash value on recovered and reclaimed R-22 could help reduce unnecessary releases. Since 2010, R-22 production and import allowances have been significantly cut back. Despite these cuts, and associated increases in gas prices, EPA has not yet measured accompanying improvements in the rate of reclaimed R-22. Without an increase in reclamation rates, system owners and other R-22 end-users will face volatile prices and uncertain access to supplies.

EPA is expecting that allowance cuts for R-22 production will encourage greater recovery, and that refrigerant reclaimers will, in fact, be offering higher “bounties” for the gas.A cap-and-trade program already worked to rid us of acid rain, but most of the R-22 is sitting in old HVAC equipment, as opposed to being emitted. Is this a possible solution?— NYTimes reader “Dave Kliman”Over a 20-year period, the U.S. cap-and-trade system for acid rain created incentives that turned pollution reductions into marketable assets. Midwestern and Eastern power plants covered under the program achieved full compliance, even exceeding targets for sulfur dioxide, at a cost that was 70-80 percent below original government estimates.California’s cap and trade program can be equally successful at reducing greenhouse gas emissions cost-effectively. The California GHG program allows for offsets generated by projects using standardized protocols. These offsets will be driving innovations among “non-compliant” entities so that the state’s targets can be met at the lowest cost.

One of the approved offset project types is the destruction of CFC refrigerant gases that would otherwise be used in leaky equipment and eventually released into the atmosphere.It is possible that this protocol would extend to R-22 and other fluorochemical refrigerants with high GWPs (global warming potential), so long as the offsets meet additionality and other key criteria.10 years ago, I worked as an inspector the EPA’s CFC program. It’s nearly impossible to catch someone actually releasing refrigerant into the air. Instead we’d go after people for record-keeping violations. It was very unsatisfying and I didn’t really feel I was accomplishing much. We did get complaints of releases called in occasionally, but again, I never had a case where we proved it. As far as I know, my former regional office doesn’t have anyone working the CFC program at this time.— From NYtimes reader “Ann”U.S. EPA regulations related to fluorochemical refrigerants have resulted in a safe and smooth transition from CFCs to alternatives that are far better for the environment. 

However, it is challenging to ensure compliance with regulations that involve tens of thousands of certified technicians servicing millions of air conditioning and refrigeration units and systems across the U.S. By law, owners of large equipment (e.g., supermarket systems, commercial air conditioning units) have to ensure that the equipment is maintained and leaks are repaired by certified technicians.  Homeowners of smaller central A/C units are not legally responsible for refrigerant leaks, but anyone servicing the smaller equipment is still prohibited from knowingly venting R-22.  While the choice to recharge leaky equipment may come down to economics (recharge vs. new unit) this choice may be short-sighted.  The unit would likely continue to require routine servicing, with increasingly more expensive recharges.We think the most cost-effective solution to promote best practices and prevent unnecessary emissions is to emphasize accountability, and to leverage market incentives.I wish the New York Times article went more into the greener coolants that are being developed. 

Shouldn’t we put our minds together and push for near 100% sustainable A/C development?— From NYtimes reader “DavidLibraryFan” Refrigerants with zero or very low global warming potential (GWP) are gaining more market acceptance, in lots of applications. This year, EPA added three hydrocarbons as acceptable alternatives in household and small commercial refrigerators and freezers through the Significant New Alternatives Policy (SNAP) program.  The newly-listed hydrocarbon refrigerants – already widely in use in Europe — can be used to replace CFC-12 and HCFC-22 in household refrigerators, freezers, combination refrigerator-freezers, and commercial stand-alone units.  EPA also published final use conditions for CO2 and HFO-1234yf as a refrigerant in new cars and trucks. Two resources on ammonia, hydrocarbons, and CO2 refrigerants are Refrigerants, Naturally and Shecco.My small town has an annual white goods collection. The town invites residents to bring down old appliances … but refrigerators and freezers cannot contain Freon.

When he asked officials how to get rid of the Freon, they said “we can’t tell you what to do, but if the line happened to be cut then we could accept your old refrigerator.”— From NYtimes reader “Fosco” Of the 9.4 million fridges reaching end of life in the U.S., about 25 percent are resold into the after market, resulting in increased energy demand from continued use of the older, less-efficient models. That leaves 7.1 million fridges to be de-manufactured. Of these fridges, the vast majority end up in landfills or metal scrapyards, where their coolant refrigerants and other hazardous materials may not be dealt with properly.  EPA’s RAD program  encourages voluntary, responsible recycling but less than 10 percent of the discarded fridges in the U.S. are managed under RAD programs.While Federal law requires recovery of refrigerants and other hazardous waste prior to disposal or recycling  (the law does not require recovery of appliance foam, also an ODS/GHG emissions source), properly recovering refrigerants adds time and labor to an already labor-intensive process.

“Cutting the line,” i.e. venting the refrigerant before the refrigerator arrives at the recycling facility, unfortunately, may be a common practice before your beloved old fridge is crushed for scrap metal. Refrigerator buy-back and recycling programs are active in many parts of the country, with sponsorship from local utilities, retailers, and some manufacturers.  Equipment owners often get a rebate towards a new fridge, with utility programs paying for older units as long as they are operational.  Appliance recyclers like JACO Environmental will pick up your old unit at your house or at a collection facility, and completely de-manufacture the fridge into its component materials. Refrigerants and even the fluorochemicals in the insulation foam are extracted under vacuum, and safely disposed or recycled.Is more innovation in store for refrigerants?  Stay tuned for our next articles.The Refrigerant Revolution, our multi-part article series, explores the environmental and economic dynamics around refrigerants and the market-based solutions aimed at their full life-cycle management.