Refrigerant Check
What refrigerant pressure readings should I have on my central AC unit.?
The reason I'm asking is that I had my evaporator ice up the other day, and was told that low freon could be the cause. Filter is good, and drain is clear. I believe I have a 4 ton system, and it's using R22 as its refrigerant. Checked for leaks at the evaporator and condensor with a "sniffer", and could not detect any leaks. I know sniffers aren't fool proof, so I want to check the pressures. Evaporator hasn't iced up since, even though we are experiencing record high temps and humidity, and will be for the remainder of the week.
You said you checked the filter and drain. Did you check the evaporator coils to see if they were clean? Low air flow can make unit ice up. Hold a good flashlight on one side of coils and if you can't see light through them they need cleaning . also check your coils on the outside condenser. If coils are clean inside and outside, prosed. If the large line going to the condenser, the suction line is sweating heavy unit should be ok. Mine did this the other day also iced up and my unit is clean as a new one and pressures are ok. On a four ton unit suction pressure should be around 60 psi. and discharge high side should be around 250 psi. Don't for get your unit has a squirrel cage blower, if blades are dirty it will not draw enough air over the evaporator, and cause icing
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The Chemistry Of Refrigeration
The environmental pressures of global warming have put increased emphasis on the need for alternative types of chemical refrigerants. The trend began in 1996, when the U.S. Environmental Protection Agency's (EPA) Clean Air Act banned the manufacture of the most common refrigerants, because they contributed to the depletion of the ozone layer in our upper atmosphere that protects earth from the sun's ultraviolet radiation. These refrigerants were known by the trademark name of their manufacturer, DuPont, as Freon 12 and Freon 22, although we will refer to them here by their generic names, CFC-12 and HCFC-22. CFC-12 is a chlorofluorocarbon (CFC), a chemical combination of carbon, chlorine, and fluorine.
Chlorine is the culprit that zaps ozone. Under the EPA guidelines, CFC-12 was supposed to be phased completely out of use by the year 2000. In its place, related chemical compounds include hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs). However, HCFCs (HCFC-22) are also slated for extinction by the EPA somewhere between 2015 and 2030. HFCs, without chlorine, have skirted the ban so far; in fact, the most widely used alternative refrigerant is now HFC-134a. All refrigerants are hazardous when exposed to an open flame. Some of them contain butane or propane mixes blended into their formulas. If large quantities of refrigerant are released in a confined area, suffocation is a danger because refrigerant actually displaces oxygen.
Breathing refrigerant can cause nausea, dizziness, shortness of breath, and even death. Thus, any type of refrigerant gas should be handled by a professionally trained technician. Environmental risks and health warnings aside, the cooling power of the modern refrigerator comes from the repeated compression and expansion of a gas. As the gas expands, it cools and is cycled around an insulated compartment, chilling the contents inside. Ammonia, new chemical blends, and even space-age technology using sound waves to cool foods are other options that have been introduced recently with some success. In 2004 the ice cream maker Ben & Jerry's installed the first thermoacoustic freezer in a retail location, developed by Penn State University researchers.
Thermoacoustics is the premise that, as sound travels through air, it alters the temperature of the air. A loudspeaker is used to create 170 to 195 decibels of sound (and yes, that's very loud) in a tube that contains inert, compressed gases (helium or argon), which are environmentally safer than CFCs. The sound causes the gas molecules to vibrate, expand, and contract. When they contract, they heat up; when they expand, they cool down. In refrigeration, the goal is to exhaust the heat generated as the soundwave is compressed and capture the chill as the soundwave expands. The loud screech emitted within the unit is muffled so it is heard as a quiet hum from the outside. Thermoacoustics cools using a type of sealed motor developed in the 1800s by Robert Stirling of Scotland.
You may hear the term "Stirling cycle technology" associated with CFCfree coolant ideas. A Stirling motor can be solar-powered, which is one of its potential "green" advantages. Another promising cooling technology is electromagnetism. A "magnetic" refrigerator can cool by repeatedly switching a magnetic field on and off. The current prototype is made with gadolinium, a metal used in the recording heads of video recorders. Gadolinium and magnets are not cheap, but the technology shows great potential for two reasons: Electromagnetism is environmentally safe (no CFCs), and does not require a compressor (no mechanical humming noise as the refrigerator cycles on and off).
At this writing, Astronautics Corporation of America in Milwaukee, Wisconsin is at the forefront of this field. Expect more technological breakthroughs as global warming headlines become more ominous. A group called Refrigerants, Naturally! formed early in this century by McDonald's, and Unilever to develop and test HFC-free refrigeration technologies, making commitments to eliminate HFCs in their point-of-sale cooling applications. In 2007 Carlsberg, IKEA, and PepsiCo joined the group. How does the foodservice operator cope with the changes and the prospect of expensive new replacements for old workhorse refrigerators? Well, if your equipment is in good repair, you probably should do nothing as long as it lasts except keep it properly maintained.
This especially means cleaning the unit's condensing coil once a month to prevent grease and dirt collection that block air circulation. If your refrigerator needs repair, you have two choices: Voluntarily retrofit it to use an alternative refrigerant, or purchase a new unit that is already equipped to use the newer refrigerants. Retrofitting almost always requires more than one service call and includes these steps: Recovering the outdated refrigerant, changing the coil in the compressor, replacing the filter or dryer, if necessary, recharging with the new refrigerant, checking performance for the first few weeks.
The EPA now has a sophisticated set of rules for refrigerator repair. The EPA certifies repair technicians and their equipment, and requires that they recycle or safely dispose of refrigerant by sending it to a licensed reclaimer. The rules also state that "substantial leaks...in equipment with a charge greater than 50 pounds" be repaired. This means if the unit leaks 35 percent or more of its pressure per year, it needs fixing. As the owner of commercial refrigeration equipment, you are also required to keep records of the quantity of refrigerant added during any servicing or maintenance procedure.
The EPA Web site contains summaries of the rules as well as lists of acceptable alternative refrigerants that don't contain the ozone-depleting chlorofluorocarbons and hydrochlorofluorocarbons. They're identified with abbreviations and numbers, such as MP-39, HP-80, R-406a, and GHG-X4, which probably don't mean much to you as a foodservice employee. However, the important points to remember are: use an EPA-certified technician, with certified equipment, to do your refrigeration repair work. Underwriters Laboratories (UL) is now authorized to test and approve alternative refrigerants, so look for the UL label on products. Keep your maintenance records updated. Violations of the Clean Air Act can result in fines of up to $25,000 per day.
If you have more than one piece of older equipment, plan a gradual phase-out or retrofit program. Don't break your budget by trying to do it all at once. This information should also serve as a caution when you are looking at purchasing used equipment. Is the owner getting rid of it because it no longer meets the environmental rules? With that, we've discussed the first major process going on inside the refrigerator: temperature reduction.
About the Author
Franco Zinzi has been involved with online marketing for nearly 3 years and likes to write on various subjects. Come visit his latest website which discusses of fridge for restaurant and refrigerator supplies for the owner of his own business.
