AIRCONDITIONING LIMITS

Usually it will get hot and trip the thermo overload on the motor. Now if the inside coils freeze up it just keeps on trucking away. Been there alot.

Hi,

thanks for your reply,

But what happens if the thermo O/L fails in a shorted condition.

(contacts welded together). And compressor keeps running.

The winding's on the motor gonna smoke.

But what happens before that ??? (to the refrigerant in the condenser)

That's what I'd like to find out without doing such a test.

Can I actually detect and know if or when the refrigerant starts to boil ???

best regards

Jens

CICUIT BREAKERS SHOULD TRIP IF CORRECTLY SIZED

Refrigerant pressure will increase so will temperature until some differential is reached where heat exchange will take place again.

The Compressor will overheat and if is properly fused, the fuse should open. Worst case scenario . The breaker will trip at the distrubution panel. Also in that sitiuation the refrigeriant has already boiled off and is in a hot gas situation since it can"t condence anymore. Internal overloads rarely fuse since there in an environment of no oxidation in a clean system free of acid. Most compressors have a external overload switch using a bimetal to open the low voltage motor control which should stop the compressor. Having a runaway compressor is rare but does happen when someone has by-passed the safetys.

Also I forgot to mention is when a compressor shorts out to ground ,the winding is open and fuses have been blown. I have never seen a compressor shorted to ground ever run. Its the end of its life for the compressor.

hi vip ;

a winding shorted to case will run if ALL THE RELATED CONNECTINGS TO GROUND ARE ISLOATED [PIPING , CONDUIT ETC ARE ISOLATED ] EXTREMALY DANGEROUS /

WHEN THE WINDINGS SHORTED BETWEEN THEMSELVES THEN IT QUIT /
a store owner did this on a compressor we had shut down /

Hi Jens,

In a refrigeration cycle the freon actually boils in the indoor coil and creates the cool air we feel. The boiling of the freon is caused by the heat in your house being absorbed.

To answer you question, The compressor pumps the freon, in a gaseous state, into the condensor. Pass the condensor is a restrictive device, we'll call it an orifice for simplification, that prevents the freon from just freewheeling in a continous loop. As the compressor pumps the freon gas into the condensor, the orifice holds back the gas creating a high pressure of very hot gas. The outdoor fan cools this gas condensing or converting the gas to a liquid. This liquid freon is metered through the orifice to the evaporator or indoor coil. The freon starts boiling when it reaches the evaporator and continues boiling all the way through until it reaches the end of the evaporator when almost all the freon has converted back to a gaseous state. When the gas leaves the evaporator it enters the compressor where the cycle starts all over again.

If The outside fan should fail the pressure would rise because the condensing is not taking place fast enough. As the pressure rises the load on the compressor increases and the heat builds very rapidly. When the load increases the current on the motor increases heating the windings, and if there is no overload or fuse the windings eventually will smoke. There is another problem that as the pressure increases the temperature increases and the oil that is circulating with the freon will break down and you will lose the lubrication of your bearing and other parts of the compressor possibly causing a siezure of them as well.

On a 85 degree day your condensor pressure would run approximately 250 lbs with r-22 freon. This number will vary from mfg. to mfg. and unit to unit. With a clogged condensor I have seen the pressure as high as 460 lbs. This is a very hot and dangerous gas. If you would try to access the high pressure side while the unit is running or not this gas can escape causing both severe burns and frostbite at the same time.

Bottom line is the ouside unit must be clean, the unit properly fused and all safety devices need to be in place.

If you don't mind I'll tell you about my experience with an air conditioner.

Many years ago we had an 18 wheel truck. It had what I believe was the condensor on the roof. It had a fan to do what the fan was supposed to do. The fan burned up but the rest of the unit continued to do what it was supposed to do. That apparently caused a blockage in the lines. The compressor kept pumping and the pressure built and built. It built up so much that it blew one of the lines going up the back of the cab. The A/C mechanic witch put it all back together told me me they will build to about 500 pounds of pressure and blow.

When it blew, we were pulling up a long steep pass in Wyoming in the Green River area for those of you who know that country. There was road construction going on with lots of people working right where it decided to blow. I was told the grade was about 13 percent in the construction zone so the truck was having a struggle just to pull the load up the grade.

It blew so hard and so loud that men were hitting the ground. It blew dust up so hard that other truckers thought we had blown several tires. They were howlering on the radio to not stop because we would never get going again. They were worried about breaking axles and drivelines trying to get going again if I plugged the road. An empty truck had just passed me and had to pull in close to avoid oncoming traffic. He thought he caused me to downshift and blow the engine and was appologizing. He heard the blast and saw all the dust flying.

The dust cleared a little and we could see that we weren't loosing blown tires but we had no idea at all what had happened and we were still moving. The engine was still screaming to get the load up the hill. The tires were still turning. I told the other guys over the radio I had no idea what had caused the explosion under the truck. Speculation was dynamite detonated that hadn't gone off when they were blowing the rock on the road.

After about 10 or 15 minutes we got to the top. We looked all around under the truck and couldn't find any damage. We were absolutely perplexed when someone looked up the back of the cab and saw that little AC line all blown to pieces.

It was a day before we got to where we could get the AC fixed. The temps were pushing 100. The mechanic said you don't want to be around when one of those lines blow. I believe he was telling the truth.

Hi,

Thanks for your report.

No I don't think I'd wanna be around when things like that happens.

Jens

You better find another mechanic Its sounds like all the safteys were jumped out and the unit was not safe to run. Good Luck!

The working fluid will not condense when the condenser coil is failed. Consequences depend on the complexity of the system. In a simple system the restricting valve or capillary tubes system rely on receiving a condensed liquid. Instead they get a hot gas. High flow rates, very poor cooling, compressor run on would be typical consequences.

Thanks for your comment,

Would you happen to know what the highest ambient temperature (deg. F)

would be allowed for the condensing coil on a split home 3 ton AC system ????

regards

Jens

130 is pushing it for R22. It depends on the unit . Extreme high ambient temps mean hard starts. dew point should be the concern

Hi Jens, I'm an air conditioning guy, I teach it, install it and size, sell, design it for a commercial AC company.

Air conditioning theory is quite complicated and efficient heat transfer utilizing refrigeration is subject to a lot of other sciences and other systems doing "their thing" properly in order for the AC system as a whole to function properly.

The unit was design by serious "smart guys" in laboratories to work properly. Since you said its a straight AC, your indoor unit's (evaporator) job is to ABSORB heat ( into the refrigerant within its tubes. ( Of course you just want the cold air it makes.)

The compressor passes this refrigerant with its absorbed heat to the outdoor coil (CONDENSER ) whose job it is to throw away this heat.

If either coil becomes dirty or blocked or is somehow different from the way it came from the factory, fins knocked over, dog pisses on the coil, plants grow against it etc., it will NOT perform as it should or could.

Think of taking a sponge and soaking up a water spill and wringing it out, next trip, don't wring out the sponge as good and when you come back to the puddle, you won't absorb as much either!

Air conditioners were critically designed to keep humans comfortable. The manufacturer's tech specs reveal the test conditions which ARI tested them under. YORK tests their outdoor units at 95 degrees outdoor and 80 degrees indoor air temp at 50% RH.

Your unit will move 3-tons ( 36,000 btu's per hour at those parameters. If the humidity inside is HIGHER, it'll produce MORE than 36 mbh (mbh stands for thousands of btu's). If it's LOWER than 50%, it'll move LESS than 36 mbh. If the temp inside is HOTTER thqn 80 degrees, it'll move MORE than 36 mbh, if its COLDER in side it'll move LESS than 36 mbh. If the temp OUTSIDE is HOTTER than 95 degrees, it'll move LESS than 36 mbh and if its slightly cooler outside, it'll move MORE than 36 mbh.

If you have a bunch of machines in a room emitting 36,000 btu's per hour, a 3-ton AC will NOT remove all this heat. About 2/3 of it's capacity can be used to lower the temperature, the other 1/3 is reserved for lowering humidity. You would have to OVERSIZE it by at least 35% to remove 3-tons of sensible heat (dry heat).

Your system was designed to have approx. 400 CFM per ton of air ( that's 1200 cfm for you) moving through the indoor coil, if your filter blocks up and it moves less air, your unit will move LESS than 36 mbh. Same with the outdoor coil, if it get s dirty or blocked...bad news.

Your unit could potentially pump approx 425 psi of pressure ( assuming its R-22) and assuming at least 30 degrees of discharge superheat, the temperature of the small copper line (discharge) coming out of your compressor could approach 200 degrees.

If you over-work your compressor so that it kicks off from its internal safeties, it causes permanent damage to the internal working parts. The internal safeties are NOT meant for repeated trips.

And yes you're refrigerant can boil but you won't hear it, its not the same as a car radiator.

A little fact that most people don't know Here in Indio Ca at the Fantasy Springs Casino where one of the original York chillers for the World Trade Center was purchased in the early 80s and was reinstalled to service the new 100,000sf casino . It is used as a stand by source of chill water when the heat is up

I don't have any experience on systems over 10 hp, but on small systems the breaker will never protect from a dirty condenser or failed fan motor.

Refrigerant boils in the low side, not the high side so that is not a factor. As the discharge temperature goes up several things happen: lube oil breaks down increasing friction, winding insulation breaks down cusing acids to form in the system, valves begin to fail.

The failure in small systems becomes an electrical failure, but it starts as a different failure.

Proper clean up after a burn out is needed to prevent the new compressor from being damaged.

To determine if the refrigerant is gas or liquid you need the pressure and temperature and a T and P chart for the refrigerant. Manufacturers of refrigerants provide these. Most refrigeration supply houses give them away or you can get them on line from the manufacturer. -- JHF

A properly sized breaker will protect against high head pressure. I went to work on a customers 3 ton unit about 12 years ago and the previous HVAC companies tech had replaced the 30 amp breaker with a 45 amp breaker because the 30 amp kept tripping. The 3 ton unit ran within its specifications after I cleaned the unit and I was able to switch back to a 30 amp breaker when I was finished. I agree this is not my 1st choice of protection. A motor overload along with a properly sized breaker are the minimum protection you should have.

Hi Guys

Thanks very much for your remarks to my initial questions,

If one of you guys would happen to know which manufacturer has a

pressure/temp chart for the various refrigerants I'd really appreciate

if he would give me a link to a webpage where I could copy the charts.

I'd also like to know the specs of the compressor oils, since one of you guys mentioned that the oil would also break down.

Now here is another question.

WHAT IN THE WORLD DO THEY USE IN SAUDI ARABIA ???

SINCE THE OUTSIDE AIR IS MUCH TOO HOT. DO THEY USE WATER AND IF THEY DO,

DO THEY HAVE ENOUGH (THEY LIVE IN THE DESSERT AS FAR AS I KNOW)

I've seen temperatures of 111 deg. F (44 deg Celsius) on the weather-channel

ALL THE BEST FROM

JENS

They probably use the same as us . I live in Palm Springs where the Temp can be 125 in Aug . I have 2 Carrier split systems cooling a 2400 sf home and it works fine. Even though its so hot outside I have my themostats set at 78 and it feels fine. When the humidity is low you can get away with a swamp cooler. You can get refrigeration charts at any A/C supply store.

I tried to deal with a HVAC dealer before and if you are not a professional in that field they are difficult to get anything out of.

Up here in Canada there are regulations making it almost illegal for the DO IT YOURSELF GUY. (I'm in norhtern Ontario).

Thanks for the help

Jens

Here is a link that may help you http://www.refrigtech.com/research.html

Thanks VIPLEATHER,

I'll try that link.

Best regards

Jens

Hey, VIPLEATHER gave you a lot of good answers...

google this fella's name JOHN TOMCZYK

He's afililiated with Ferris State University and he writes refrigeration and air conditioning books. Most books on this subject are hard to digest, in fact they make simple concepts complicated and scary. This guy is opposite. If you're serious about learning about HVAC, get anyone of his books, guarantee you'll like them.

I have one called TROUBLESHOOTING and SERVICING MODERN AIR CONDITIONING and REFRIGERATION SYSTEMS. ( Isbn 0-912524-94-4) I use it to teach out of.

Hi Sniccus,

Thanks, I'll go to CHAPTERS bookstore and look at the book.

If John can make difficult things look simple, then that's for me.

Did you get my email. ????

all the best

Jens

http://www.hantech.com/support/documents/HTCPressureTemperatureChart.pdf

Hi VIPLEATHER,

I looked at those temp/press charts.

Does that mean a system could be designed and built to pump BTUs

from a cooler box with a temp of 50 deg F (+10 celsius)

to an outside ambiant temperature of 155 deg F (+68 deg celsius)

without frying the compressor or breaking down the oil.

Or is that too much to go for ?????

all the best

Jens

Jens The charts are designed for a tech that understands the different types of refrigerates that are used in differant applications and equipment design. There are so many types of systems out there and to understand these systems you really should have a basic understanding of the refrigeration cyclye. To give you an example : Water boils at 212F at sea level ( 14.69 psi Atmospheric presure) this the process of removing heat is the same of certain freon's design to remove heat in the process of evaporation in a contained vessel or element (evaporator) at different presures. The compressor is like a pump pushing (compressing ) freon through the basic parts of the refrigeration cycle. There are many of books out there which gives you the basics. GOOD LUCK

Hi Guest,

Thanks for your advice,

I'm gonna take a look at the book that John wrote

the one Sniccus uses for teaching.

Up here in Ontario we have "Chapters" book store and they can

order any book still in print.

all the best

Jens

2 points: First, I renew my statement that a circuit breaker will not reliably protect a system from a dirty condensor or bad condenser fan. In over 40 years I, too, have seen some strange things. The crazyest was an ice machine that a tech put the wrong compressor in, a 120 volt compressor in a 230 volt machine. It ran fine for 3 weeks with out shutting down before burning up. Not off on bin 'stat, it ran 3 weeks.

I still don't believe that a breaker will ever protect the compressor from a diry condenser without numerous nusiance trips.

Second, from -10f to +155f is probably too big a step in one stage. Also off the shelf stuff is probably not ment to handle that high of a condensing temperature. I am shur that one of the refrigeration equipment manufacturers can advise you of and supply a compressor that will handle that temp with special oil, but it may have to be a 2 stge system. -- JHF

Those "nusiance trips" would be caused by the compressor current being too high because the condensor is clogged up. The nusiance trips are an indication that something is wrong. This is the breaker doing its job, protecting the condensing unit.

Your Condensing Unit should have a LP switch & a HP switch unless they were removed or bypassed. They are designed for protection. A low ambient switch also offers protection.