Icing up due to overcharge?

[fat eddy]

An overcharge can cause freezing, but it is a complicated scenario, typically it wont.It is more likely that it will freeze with a low or normal charge with other poblems such as airflow also being a factor.

[chill factor]

I've got news for you guys. When you charge a system, you mainly keep your eyes peeled for compressor amps, suction pressure, head pressure and most important SUPERHEAT(SH). SUPERHEAT is calculated by SUCTION LINE TEMP(SLT) minus SATURATED SUCTION TEMP(SST). For high temp refrigeration(Air Cond.), a SH of in between 10F - 15F can be expected. Some systems are designed as high as 25F. In a capillary metering device system, as you add refrigerant, your superheat heat decreases. Since SST is approx 40F and if you begin to overcharge your SH decreases. This means that your SLT drops below 40F and if excessively overcharged, your SLT can easily reach below 32F.
If there is excessive humidity in the ambient, thus air will lose its humidity onto coil and suction lines and compressor thus icing up due to SLT being below 32F.

As far as a TXV system, overcharging will backup into condessor increasing head pressure eventually increasing RLA of both compressor and cond.fans. This will make one or the other or both shut off on overloads or if system is equiped with a high head pressure switch, it will shut AC down. The evap will be controlled according to SH as others have said.

Therefore, yes you can ice up a system with an overcharge with a cap tube system only!

[ac/dc]

I agree a system that is overchaged with "no other problems" will not freeze. The pressure would be elevated.
Now low and med temp refrigeration is a different story...
ofcourse the evap will freeze with overcharge.. and correct
charge for that matter

[chill factor]

Originally posted by ac/dc
I agree a system that is overchaged with "no other problems" will not freeze. The pressure would be elevated.
Now low and med temp refrigeration is a different story...
ofcourse the evap will freeze with overcharge.. and correct
charge for that matter

Im assuming you didnt read what I posted. If you did you should re think your logic.

[Andy Schoen]

Originally posted by airworx
you guys are wrong however about how a txv works.
if you overcharge a system that has a txv and we are not talking about an orfice. but a txv will close off to keep the superheat up to its setpoint say 15 degrees. as more refrigerant is added it will have to close off more and more to keep the superheat up and that will cause the suction pressure to drop.

airworx, you're a bit confused a bit here. Let me help you out.

Suction pressure is simply a function of heat load on the evaporator and your compressor/condenser capacity. If the TEV is operating properly, it will modulate refrigerant flow such that it will increase refrigerant flow into the evaporator at higher load conditions, thus raising suction pressure, and reduce refrigerant flow into the evaporatir at lower load conditions. This is due, of course, to the fact it controls superheat at the evaporator outlet. It does this function much better than a capillary tube or fixed restrictor.

The key here is your heat load on the evaporator. It is the primary variable in determining your suction pressure.

The TEV doesn't care about an overcharge system. It will continue to control superheat regardless. An overcharged system, however, will reduced your compressor's capacity and efficiency, which will cause higher than normal suction and discharge pressures.

You might find the following of interest. http://www.sporlan.com/10-9.htm I wrote its original version

[kerndt]

chill factor

THIS STATEMENT IS WRONG!!!

This means that your SLT drops below 40F and if excessively overcharged, your SLT can easily reach below 32F. If there is excessive humidity in the ambient, thus air will lose its humidity onto coil and suction lines and compressor thus icing up due to SLT being below 32F.

HOW IN THE WORLD IS THE COND. FAN AMPS GOING TO INCREASE!!

increasing RLA of both compressor and cond.fans.


AND YOUR CONCLUSION IS WRONG!!

Therefore, yes you can ice up a system with an overcharge with a cap tube system only!

This stuff is basic theory, how can you possibly not understand it. I can’t imagine how you troubleshoot refrigeration problems without understanding the basics. You guys that believe this better run back to the texts books, please.

[kerndt]

Airworx,

I can’t believe that you’re sticking to your misguided line of logic. I could teach a monkey how a TXV or EXV works.

What concerns me most is that you always are quick to give advice, and you don’t understand the basics.

That’s like the blind leading the blind. You may have years of experience, which has given you some instinctive troubleshooting abilities, (troubleshooting without logic or understanding) that’s not enough, to advise or teach others.

You know what a TXV does, but you don’t know how it does it.

Many so called parts changing service techs work in the same manner, after changing enough parts it bound to get fixed.

Understand, it’s you “who doesn’t understand refrigeration”, take a step back, listen and learn from the people here that want to teach you.

The good thing about this thread is, a lot of the misunderstanding is being corrected.

[ac/dc]

Chill Factor,
Your right I didnt see your post before I posted. now that
I have I think you might want to rethink YOUR logic.
yes superheat will decrease on a overcharged cap tube sys.
but suction pres will increase and the evap will be well
above freezing temp. unless there is inadequate load on the evap coil. Then freezing would be caused by low load
on evap...not overcharge. Explain how cond. fan amps increase in a overcharged txv sys.

[clydemule]

Originally posted by kerndt
chill factor




HOW IN THE WORLD IS THE COND. FAN AMPS GOING TO INCREASE!!

Wondering about that myself.

[chill factor]

Easy guys. The cond fan will rise in amps. It can or cant be a drastic rise. We're just getting into cooling season soon in Toronto. I'm still in the transition of heating to cooling.
As i quickly think about it, the excess heat in condensor area will add to the amps of the motor while its operating. The motor depends on the air coming across it to cool it down. If that air is too hot, it will transfer into the motor. Heat travels from hot to cold.

Have you ever noticed how hot a cond fan motor gets if cond is plugged. Yes i know that the static also has something to do with it, but so does the ambient temp coming across the motor.
I hope you guys see how the compressor amps will go up in a TXV!

[Edited by chill factor on 04-09-2005 at 09:50 PM]

[chill factor]

AC/DC

Your thinking about inside the system. If your SLT is dropping dont you think the surrounding air has a dewpoint which will condense on the lines. If SLT and I repeat SLT is below 32F regardless of ref pressure that condensation will form ice!

[airworx]

are you guys deaf. i said a refrigeration system and the exv on a flotronic chiller. i did not say an air conditioner.

also when you overcharge a system head does go up but on a txv system the tx bulb senses temp not pressure and as the temp drops the pressure in the bulb drops the spring and evap pressure overcome this pressure and pinch off the valve
which causes the suction pressure to drop.
now i know theres someone out there that knows how this thing works because you guys apperantly do not.

i think this is the commercial posting if not im sorry.

[Edited by airworx on 04-10-2005 at 10:37 AM]

[Carnak]

Originally posted by Andy Schoen

Originally posted by airworx
you guys are wrong however about how a txv works.
if you overcharge a system that has a txv and we are not talking about an orfice. but a txv will close off to keep the superheat up to its setpoint say 15 degrees. as more refrigerant is added it will have to close off more and more to keep the superheat up and that will cause the suction pressure to drop.

airworx, you're a bit confused a bit here. Let me help you out.

Suction pressure is simply a function of heat load on the evaporator and your compressor/condenser capacity. If the TEV is operating properly, it will modulate refrigerant flow such that it will increase refrigerant flow into the evaporator at higher load conditions, thus raising suction pressure, and reduce refrigerant flow into the evaporatir at lower load conditions. This is due, of course, to the fact it controls superheat at the evaporator outlet. It does this function much better than a capillary tube or fixed restrictor.

The key here is your heat load on the evaporator. It is the primary variable in determining your suction pressure.

The TEV doesn't care about an overcharge system. It will continue to control superheat regardless. An overcharged system, however, will reduced your compressor's capacity and efficiency, which will cause higher than normal suction and discharge pressures.

You might find the following of interest. http://www.sporlan.com/10-9.htm I wrote its original version

It's amazing that people won't take winning tips straight from the horse's mouth

[Dowadudda]

The friggin guy who pratically designed the TXV, wrote the book on TXV's, and the guy who practically runs the company who makes the TXV's comes on here and tells Airworx he is wrong, and then he still think he's right. What an arrogant and ignorant guy. That is insulting to me.

[Andy Schoen]

Originally posted by airworx
also when you overcharge a system head does go up but on a txv system the tx bulb senses temp not pressure and as the temp drops the pressure in the bulb drops the spring and evap pressure overcome this pressure and pinch off the valve which causes the suction pressure to drop.

I think I understand the problem here. The TEV's sensing bulb, of course, doesn't sense pressure. But the valve does. The pressure it senses is what's referred to as equalizer pressure. A bit of a misnomer, perhaps, but that's what it's called. An internally equalized TEV senses this pressure internally. An externally equalized valve senses it via a third connection on valve which is connected to the outlet of the evaporator, normally with a 1/4" OD line.

At the TEV sensing bulb location, temperature is not being controlled.

At the TEV sensing bulb location, only superheat is being controlled. You can't assume equalizer/suction pressure will stay the same when the bulb temperature drops. In fact, you can expect it to drop also. So the question becomes: what's causing suction pressure to drop? Low load, yes; low airflow, yes; overcharge, NOT.

The situation with an EEV is a bit more complicated due to the fact the EEV controller may well be controlling more than just superheat. But if the controller is simply controlling superheat, the result will be the same.

[Edited by Andy Schoen on 04-10-2005 at 06:34 PM]

[Andy Schoen]

Unfortunately, I only got a 72 on the a/c CMS, which is worse than the 75 I got on the refrigeration test I took a year ago.

I did poorly on absorption systems... Nailed psychrometrics, though, as expected...

I'm resigned now that I'll have to actually study for one of these damned tests to pass it

[twcpipes]

I have to go back to my original system of a
Fixed orifice.
Now I will add a system:
5 ton compressor/condensing unit. 5 ton evaporator coil.
3-1/2 ton load on said evaporator. Air flow at 225cfm/ton
due to plugged coil. Evaporator temperature at 25 degrees with 10 degrees of superheat. 70 degree day.
I, like many servicemen merely put on gauges and say, "Oh the suction is too low I need to add gas. Screw putting a suction side thermometer on". Of course I haven't done that since '66 as I recall.
I add gas and loose the superheat and make the refrigerant temperature in the whole of the evaporator side 28 degrees, up from 25 degree equivalent pressure.
Did I not then have the capability to create ice with any water particle that comes in contact with the evaporator tubing which is now at 28 degrees? Especially since I have reduced airflow?
I did not gain any load by adding refrigerant. And the head won't necessarily go high enough, quickly enough to raise the suction above the 28 degrees since the condenser is capable of 5 tons.
Need to run the graph I guess.
Please explain to all on the thread WHY this cannot happen so everyone knows.
Thanks, tom

[john dalton]

Dear thread,

Good morning everyone. After reading all the above posts I can see that there has been quiet a bit of discussion deviating from Hsteiner’s original question to this thread. Since I’ve decided to step into this complicated and multifaceted thread I’ll start by giving my own answer to his original question of:

“A co-worker insists that a overcharge on a AC unit can result in iced up condition.
I always thought icing was caused by undercharge or low airflow so I disagreed with him.
Who is right?”

Based upon the lack of additional equipment information, data, before and after operating measurements, and conditions, I’ll try to answer the question in the spirit “I think” it was asked.

Being completely accurate regarding the above question, I can only conclude that unfortunately NEITHER of you are right.

Your co-work is NOT right because based upon a normal operating system with no other problems or deficiencies, overcharging an “air conditioning” system WILL NEVER UNDER ANY CIRCUMSTANCES cause the system to ice up period.

You are NOT right because although an undercharged or low airflow system can cause the unit to ice up, there are many other conditions that will generate the same symptoms as well.

My next post will comment on some of the deviated questions and comments spun off of this original question.

Respectfully Submitted,
John J. Dalton

[john dalton]

Dear Twcpipes,

Regarding your previous post:

“Please explain to all on the thread WHY this cannot happen so everyone knows.

Based upon the operating conditions, measured data, “and operational problems” of your hypothetical system, I would have to conclude that ice would in fact form from anywhere downstream of the capillary tubing all the way to and including on the exterior shell of the compressor.

Although the above referenced air conditioning system would form ice on it under the above overcharged conditions, the ice would not be a simple symptom of the overcharge, but would in fact be a product from the root cause of the system before the excess refrigerant was introduced into this system, namely the restricted evaporative airflow (225 CFM/ton as you stated).

Respectfully Submitted,
John J. Dalton

[Andy Schoen]

No doubt it is possible to overcharge a system and have insufficient airflow and create ice, all else being correct with the system. With a fixed restrictor system, the overcharge will cause floodback, and the overcharge cannot be so great as to cause suction pressures to be greater than say about 50 psig on R-22 if one expects ice to form. If a tech is mistakenly charging a system to overcome low airflow, however, he will typically charge the unit to a more reasonable suction pressure, 60+ psig, resulting in no ice formation, and greater floodback.

A system with a TEV will behave similarly, though the TEV should prevent floodback as it would control superheat.

As john dalton points out, however, the problem here is low airflow. The overcharge is not the cause, but simply the result of a mistaken attempt to resolve the insufficient airflow problem.