Checking charge on a big system (100 ton)

[amickracing]

I'm posting this question for Dad and a co-worker who are fighting with a big system. I'm very green to the service end of things, but I got as much info as I could think from them to post here, I'm sure I'm missing some, post what I'm missing and I'll get back, but any info you can give in the mean time is greatly appreciated.

It's a 100 ton trane cooling system thats at the local K-Mart. A new compressor was installed last year, it burnt up (don't know the details on why). Dad and his co-worker replaced it recently and attempted to do a start up on it today.

They think it holds approx 300 lbs of R22, it has a cooling tower (water cooled condensor). It has 3 txv's that feed seperate evaporators, a site glass is mounted about 8' before the TXV's. When they 1st start it up they get a brief flash of bubbles in it, but it clears up very fast and from then on out it remains clear. Head pressure runs around 150 and suction is approx 72. Superheat was around 0-1 deg, so they began to remove some freon to bring it up a bit more. They removed 80-100 lbs of freon, pressures stayed virtually the same, superheat stayed the same and the site glass remained filled (no bubbles).

Also, on the motor end of the compressor, when they 1st started it moisture would condense on it very bad, enough that it would run off and pool on the floor. After they removed the freon it still sweats but not near as bad, barely even dripping on the floor.

It was in the mid 70's today, and the inside of the store was in the mid 70's aswell.

They shut the cooling tower down, as soon as the fan and pump shut off the head pressure shot right up to 280 psi.

Thats all the info I can give you now, hopefully it makes some sense and you guys might be able to help point them in a direction to trouble shoot this.

They are going to do an amp draw and check the subcooling tomarrow along with some other things but I can't remember exactly.

Thanks guys!

[hvac3901]

I guess were talking about a chiller? you mentioned a pump and a tower, but that dos'nt mean anything definitive. I hav'nt seen too many stores in my area (mostly tilt-up construction for that size place) that would use a chiller.

Going with my assumption i would say you might have to look somewhere other than on the dx side first. Is the pump the right size? is it working properly? and is the evaporator clear?


Coming back to this second time...

system issue killed compressor, that syptom was repaired and system issue was not. now the symptom showed again and the system is still damaged.

[Edited by hvac3901 on 05-18-2005 at 10:43 AM]

[Diceman]

It has a receiver too somewhere I bet.
250-300 lbs is probably about right. That head seems low but you said it was a cool day and not much load, the compressor sounds like it ain't loading up yet.
Sounds like this is the first big unit they ever worked on.
Anyway, if the entire evap is cold and the head is OK, and the glass is clear, let it be for now. Go back when it gets hot and double check it.

[Shophound]

EDIT: I reread your post and see we are working with a DX coil. We could also be working with a compressor that has capacity control -do the three TXV's on the evap have solenoids on the liquid line for capacity control? Does compressor have suction pressure or solenoid suction cutoff unloaders? Is the air handler possibly either a constant volume air handling system or a variable frequency drive with variable air volume boxes distributed throughout the store?

All the things I listed above will affect the performance of the system under various loads. Given that, the most poignant thing I picked up from the info you gave was the condensing head pressure and the low side superheat. And that when the tower was shut down, the head pressure climbed.
This leads me to ask if the cooling tower has any provision for low ambient operation. Mid-seventies may not seem like low outdoor ambient conditions, but for a water cooled sytem using a cooling tower it can be, since we're dealing with wet bulb temperatures vs. dry.
Does the cooling tower have any way to cycle the fan or bypass water as the ambient temperature drops? If so, I'd check to see if these controls are working correctly. If not, your dad may want to recommend to customer that said controls be installed...it may well save the customer the cost of losing another compressor.

To check this system as it is under these conditions, I'd shut the tower fan off but leave the tower and condenser cooling water pumps on (is tower an open circuit or closed?). Also see who made this system and what the OEM wants for condenser approach temps.

[Edited by shophound on 05-18-2005 at 10:00 AM]

[john dalton]

Dear Amickracing,

You’re correct in your first assumption that you’re missing some items, in fact, quiet a bit. Some of these items might have been missed because you were not there at the jobsite observing the work, still others might be missing because your Dad or coworker did not perform the test, or obtain the information. But in an effort to help you and your Dad out, let’s try to put this thing together my friend.

At this point I’d like to separate this post into three different sections, the first section will be for this forum to obtain information on both your Dad, and the refrigeration system at hand, the second section will be analyzing the limited information you provided, and the third section will be our recommendations at this time.

Section I

We need to know about your Dad and coworkers experience with this particular type and size of HVAC system. Lets not pull any punches here and be honest, if he has the experience, background, and capability to perform the service tests and checks on this system, that’s good, if not, let us know upfront so we can walk you and him through it a little slower and with a bit more detail. Based upon the information on your original post, I can’t tell if he, you, or both of you missed on several preliminary things that should have been completed within the first few minutes of startup of the system.

Next, we need to know about this particular system, Make, model, and serial number of the 100 ton Trane water cooled condensing unit, what type of tower, I’m “assuming” its an open type based on the information provided, the liquid line separates to three different TXVs and services what, cooler barrels, DX coils, ect. What about the air moving equipment, is it VAV or fixed, is it a double duct system, dedicated heating or cooling system, mixed air, ect. How is the liquid and suction lined piped, is there liquid and suction line filter/driers, suction line accumulators, ect. What about the controls, what controls the compressor(s), are there solenoid capacity controls on the compressor, what controls them. And lastly, what was wrong with the old compressor specifically, what killed it, was the problem in the compressor that was replaced, or is it still in the system waiting to kill the new compressor, what exactly was done in the process of replacing this compressor, the discharge and suction valves closed, refrigerant and filter/driers replaced, evacuation, ect.

Section II to follow……..

Respectfully Submitted,
John J. Dalton

[john dalton]

Dear Amickracing,

Section II

Let’s outline what we do know of this system at this time:

100 ton Trane water cooled condensing unit (assumed to be open type water tower)
History of compressor failures (two within a year)
System “might” hold 300 pounds of #R-22
System has three TXVs feeding three separate evaporators (assumed to be DX coils)
Operating conditions at startup of the following:
150 discharge pressure
72 suction pressure
Superheat of 0 to 1 degree (calculated suction line temperature 42 to 43 F)
Compressor sweating profusely on motor end
Outside air: mid 70 degrees
Operating conditions after 80 to 100 pounds of #R-22 recovered of the following:
150 discharge pressure
72 suction pressure
Superheat of 0 to 1 degree (calculated suction line temperature 42 to 43 F)
Compressor sweating on motor end
Outside air: mid 70 degrees

Although the above information is limited, we still can draw three distinct conclusions from it:

The discharge pressure is too low
The suction pressure is too high
The superheat is extremely too low

We also can make a conclusion statement from the information above:

Left operating, this system WILL DISTROY this compressor in either the very near, or at best near future.

Section III to follow

Respectfully Submitted,
John J. Dalton


[Edited by john dalton on 05-18-2005 at 11:11 AM]

[john dalton]

Dear Amickracing,

Section III

The discharge pressure needs to be raise to somewhere between 185 and 200 PSIG based on the TXVs required 100 PSI delta P. In order to accomplish this we will need to know what type of capacity controls, if any, are available at the water tower, or on the condensing unit itself, namely condensing water regulating valves. If no capacity control is available, not likely, then you need to cycle the tower fan off and on to raise the tower’s water temperature to increase the discharge pressure of the condensing unit.

Next, you need to verify that all TXVs are open, that all air moving equipment is operating with clean filters and full airflow, and if the system is a VAV system, that all VAV thermostats are calling for cooling.

Finally, you need to start the system, allow it to run for at least ten minutes (20 would be better) and record the following information:

Outside air temperature
Compressor discharge pressure
Compressor suction pressure
Compressor discharge oil pressure
Liquid line pressure
Suction line temperatures at the exit of all three evaporators and at the compressor
Liquid line temperatures at all three TXV locations
Compressor FLA or RLA
Compressor actual running amps
Entering/leaving wet/dry bulb temperatures at all three DX evaporators (assumed)
Liquid line sight glass observations
Compressor crankcase sight glass observations
Entering/leaving condensing water temperatures
Compressor unloader operation (are unloaders energized or not)

Yes, this is a considerable amount of information to obtain, but without it, a service technician is only guessing at whether a refrigeration system is operating to full capacity, efficiently, and safely. The above information will not only confirm whether a system is working, but will actually point you in the right direction if its not.

Please post the results of your actions, and the operating readings here at this thread for further help.

Respectfully Submitted,
John J. Dalton

[john dalton]

Dear Diceman,

You giving summer discounts on your posts? They use to cost $1.59, now I see they’re down to $1.00. Is it because this thread is not as complicated or frustrating as “Cooling a small server room”? What gives?

Respectfully Submitted,
John J. Dalton

[john dalton]

Dear Diceman,

Regarding your previous post:

“Anyway, if the entire evap is cold and the head is OK, and the glass is clear, let it be for now. Go back when it gets hot and double check it.”

How long do you think they’ll have to wait to double check it with a superheat of 0 to 1 degree F? Will this be a race to see what comes first, the hot weather or the destruction of the compressor?

Based upon a superheat reading of 0 to 1 degree, don’t you think they need to adrress this problem NOW?

Your comments are appreciated.

Respectfully Submitted,
John J. Dalton

[Diceman]

If I answer you John, my rate is going back up to $1.59....just so you know.
At this point I'm not sure they measured the SH the right way. All I am saying is given their info and experience a simple response is what they want.
IMHO, they need to sub out to someone who has worked on these befroe and let him take a look at it.
I'm quite sure there are many things missing here.

[john dalton]

Dear Diceman ,

Regarding your previous post:

“If I answer you John, my rate is going back up to $1.59....just so you know.”

I see……..the deduction in your rate is not because of the jobsite, but the company that is there….I can live with that. And for the record, I think its worth the $1.59 price tag for your posts, they are humorous in nature, and informative at times.


”At this point I'm not sure they measured the SH the right way.”

I would have to agree with your reservations as to the above statement my friend.


“All I am saying is given their info and experience a simple response is what they want.”

And that is where the problem lays my friend. It’s like a person calling a surgeon over the phone and asking how large of an incision to make in the chest to work on the heart. A simple answer of 25 to 30 cm (an uneducated guess as to the actual size) would be the right answer, but…………….do you see my point?


”IMHO, they need to sub out to someone who has worked on these befroe and let him take a look at it. I'm quite sure there are many things missing here.”

Again my friend, I would have to agree with your assessment of the above project based upon the limited information available at this time, and it’s the missing things that always concern me the most.

Keep posting that $1.59 charge my friend.

Respectfully Submitted,
John J. Dalton

[Diceman]

I have a new friend.................:D


Due to the poor economy, runaway federal defecit and the struggling stock market, I have decided to keep my posting rate at $1.00....

[double bubble]

Don't forget discharge line temp .

[john dalton]

Dear Double bubble,

Given the vast amount of information I requested from Amickracing, I did not see a need to obtain that particular reading, but given the fact that you have requested it, I would concur as well.

Discharge line temperature 2” from compressor service valve

Respectfully Submitted,
John J. Dalton

[secorp]

I have nothing to add to this thread at this time. say hi to your dad and his friend, awaiting your reply for requested info.

Respectfully submitted.
John Doe Secorp. :)

[gasnowman]

Gentlemen,

With all due respect. Kmarts are notorious for the custom built central station in North America. Though I have seen many Aaons and Carrier package rooftops. I would strongly recommend that if you have an open drive semi-hermetic compressor, model E or F that you get a handle on that head pressure and compressor superheat. Failure to find and correct such a systems problem will result in another failure. American hermetics is the national supplier here in the southeast. First I would find out why the first compressor crashed. Sounds like your slugging her away with liquid.


PS John Dalton are you bored or what? It's nice to see a fellow RSES member involved. If you ever move to the Scenic City of Chattanooga,TN look me up. would be more than glad to exercise those talented creative writing skilled hands you have.

[seaboard]

Stick to the basics. The system wants to tell you what's wrong and all you have to do is perform the right tests and then the proper "surgery" to borrow Mr. Dalton's analogy. I posted this once before and expected some controversy for oversimplifying the complex refrigeration circuit but it didn't happen.
Here's a chart that may help you out. Sometimes you can have a combination of problems and some problems appear different on a fixed metering device versus a TXV but this is a pretty good reference.

LOW ON CHARGE
head low
suction low
compressor amps low
superheat high
subcooling low
delta temp low

OVERCHARGE
head high
suction high
compressor amps high
superheat low
subcooling high
delta temp high

POOR EVAPORATOR
head normal or low
suction low
compressor amps normal or low
superheat low
subcooling normal or low
delta temp high

POOR CONDENSER
head high
suction high
compressor amps high
superheat high
subcooling low
delta temp low

RESTRICTION (liquid side)
head normal or low
suction low
compressor amps low
superheat high
subcooling high
delta temp low

BAD VALVES
head low
suction high
compressor amps low
superheat high
subcooling low
delta temp low

[flange]

I once heard a compressor humm just before it tripped the breaker. guess it didnt know the words.

[Dowadudda]

0 t0 1 degree superheat.

Yeagh, your flooding.. Why? Check your delta T acoss that coil. And then go find why that gas aint boiling off in that coil. I bet you got no air across that coil.

If superheat was taken the right way.

And while were at Delta T's and Superheats lets go ask for Subcooling too.

[Carnak]

[Edited by Carnak on 05-19-2005 at 02:15 AM]

[paulturnkey]

sounds like system is well over charged check l.l sub cooling to verify

[amickracing]

Well it's been too long since I've been able to get back to you guys on this matter. I couldn't get on this board yesterday when I had the time (must have been down), next thing ya know it was bed time... anyway, have no fear, I'm here now lol.

Ok, here's some more back ground on things... The business Dad and his friend work for has had this K-Mart account for 2 years or so, but the guy who knew a fair bit about it quit and went elsewhere. Dad has a good background on service work (30 some odd years doing appliance repair and 8 or more years working for this company doing service, but never really got into these huge units, mostly just furnaces, rooftops and everything in between). His friend, well, he's not a great service tech, but he's not the worst either. Some how this job got thrown into his lap, and Dad was sent to help him out. That company does have one guy who I know could fix just about anything HVAC related, he's got 30+ years doing service, install, controls, you name it. But he's in a different department, and that company works so well as a team lol, since it's not his department's problem, he's not going to worry about it.

Ok, so back to the story of "one hot store". They had more time yesterday to do more checks on stuff they either forgot/missed/didn't have time to do. Turns out the system was over charged by around 200 lbs. They kept pulling it out until stuff started changing. I haven't gotten to get too many of the details (yet, printed this off for him to read) and I'll get some more info back to y'all. But from what I do gather the reciever had to be full aswell as most of the "barrel" (what ever that is). So the general advice even with poor info about it being over charged was right.

I'll be sure to update this again when i get more info. Thanks again guys!

[freonrick]

if they took 200lbs out and they have 100lbs left for a 100ton unit they will be undercharged. even if it was overcharged you should not be flooding. the txv should allow the excess freon to store in the reciever. all the old kmarts that had these systems had large recievers if some one didnt take it out. kmart use to only allow 2 filter changes a year wether it needs it or not. someone that knows that type of set up needs to go through it from end to end. follow the advice from the other post.

[Shophound]

I still say you really have to watch your step regarding charges on any system with capacity control.

I also haven't heard any mention anybody on this job has checked airflow, or said if there's any kind of variability to airflow, such as a VFD or VAV's. If your airflow is below design then the superheat will be low as well with a normal charge.

I'm thinking your dad's pulled out a lot of gas from this pig, and when the weather really heats up it might come back to haunt him. Just from my limited perspective through an internet wire I'm seeing possibly a compound problem...inadequate airflow coupled with a cooling tower that's not regulating condenser water temperature correctly.

I'm with the others...find a guru for this rig and learn from him.

[Dowadudda]

The Kmart Central Station set ups. Which most are not the same but are similiar are easy to pick apart.

I can tell you one thing. There aint nothing freeqing the fan. If there was, I would freeq. Kmart is the cheapest crappy place to do work for. It's incredible.

Basically, Big Indoor fan. Big DX Evap. Maintain 55 degrees, stage the coil with LLS valves. The Pumps are usually old POS tranes with hydraulic for unloading. Some water cooled with a barrel and tower, some air cooled with the condensers on roof. There simple. And mostly in ****ty condition due to Kmart being cheap.

[hitekrednek]

I must agree. The company I used to slave away for, had the Kmart contract here in Co a few years back. I've never seen a bigger pile of mis-matched garage sale junk thrown together in my life. With the exception of some stores with new Aaons, (which aren't maintained worth spit), most of whats here in Co, was under the "don't fix it till 100 customer's complain it's too hot/cold" rule. Some of the stores I've seen manager's out on the roof tryin to comb and clean coils.

[addison]

Is this a new compressor or rebuilt if new Then trane techs would gladly come out and help with the start-up. We have a 125 ton trane twin screw chiller here at the plant that we use for process chilled water. So i have worked with Trane Techs for several years so I know they can help, they may charge you for a service call but thats better than fighting it.

[frontbug]

Hi I just skimmed through but have you checked the txv's they may be open to far (they can be adjusted) causing the low s.h. this may be what was killing the old ones . We do some kmarts and the old junk is crap. all of ours have 3 60 ton tranes with 2 txv's each.
And have changed all 6 txv's due to low flow just stopped up htey were 32 yrs. old . correct me if i'm wrong but if the unit is not loaded it should still maintain superheat .

Also check the hydrolic unloaders if these have them and make sure they are adjusted correctly Kmarts call center has the info and will fax this to you.

But it seems that you are having to remove freon to raise sh should be that the txv's are not metering properly

This is just my $.02 Btw if you don't have good return gas temp the oil will over heat and break down and comp will dye in about a year sump temp not over 95 deg.

Let us know

[the_guru]

Future concerns.

I haven't heard a thing on how the old compressor died.
In my opinion it would be very important to distinguish what made the last compressor(possibly even one before that) to die.

I think it's terrific that everything seems to be running well at the present time.However,what will be done when the new compressor dies due to improper knowledge and/or repair?
Just throw another one in!?!

With all due respect,I suggest having a professional inspect the work that was performed to be sure the job was done correctly.

[mike grabowski]

if you have a txv you dont adjust superheat by removing freon. by removing or adding freon to a system with a txv you are adjusting the subcooling.

the txv's may need to be adjusted to give the system somemore superheat.

i have heard tha kmart usually uses a watercooled condenser with an airhandler and a dx coil. i am not sure about it being vav though.

i agree at with the superheat that low it maynot be long before the compressor sucks liquid. this problem needs to befixed asap.

[Dowadudda]

Originally posted by addison
Is this a new compressor or rebuilt if new Then trane techs would gladly come out and help with the start-up. We have a 125 ton trane twin screw chiller here at the plant that we use for process chilled water. So i have worked with Trane Techs for several years so I know they can help, they may charge you for a service call but thats better than fighting it.

Trane trane the choo choo fricken trane. WTF is going on with your trane.

Dude,

Seriously. A process chilled water screw chiller twin, is way beyond the tech that can service the Kmarts.

Trane would walk on a kmart site and quit then and there. I can hear em now.

"I aint working on that ****"

[denis]

Sorry, have'nt read all posts. I have experienced similar problem with a K-MART murdering compressors. Through years of service different companies/techs adding adding oil to compressor. Accumulator (15 ft. off floor, ceiling heighth, hard to check, with no oil return to compressor) was full of oil. Removed gallons. Hope this helps.

[esdd]

I've worked on most all of the K's in KY, southern IN, and OH. Does anyone know when the last time the tubes in the condenser were cleaned? Probably not anually as needed. most of the ones where I pulled the condenser heads left an inpression of the heads in the calcium and junk in the condensers, also there are strainers in the cooling towers and piping before the pumps, are they clean? What temp is the tower fan switch set at? 300-400 lbs of gas was the average charge in these systems. Do you have solenoid valves on the lquid lines, or just solenoids in the txv equalizers to shut the valves down? Does the system have the original controlls with the novar system doing start/stop, or has the novar controller taken over all of the unloader sequencing and temp controll of the central station as well. Both ways were common. Do you have the old Barber coleman controlls still in place? What compressors do you have, Tranes, Carlisles, or Worthingtons? There are so many questions that have yet to be answered before a good response can be given.

My best guess is that your condensers are extremely dirty, your cooling towers are scaled and the power heads on the txv's have failed.

I highly reccomend that you find someone familiar with this type of system before the replacement compressor is trashed. I saw a contractor that I would guess had about the same experience level as you described change a compressor each year. After going through the store's logs, he thought this was normal, as the previous contractor changed compressors frequently. The store never cooled right as the systems were never charged more than 30% refrigerant capicity. I usually took about 100 - 200 man hours to bring a store to a reasonable operational level. I've seen condensers so bad that the tubes had to be drilled out. Goodway makes a tube auger for their tube machines that if you can get the first 6" if tube clear it will auger out the scale to a point where chemical cleaning is effective. the auger is designed to be very hard to puncture a tube with, but I always got the regional maintenance directior to sign off before cleaning tubes.

[beenthere]

Did they check the water flow for the barrel.
That could drop your superheat, if it was to low.

[double bubble]

Always do a compressor tear down to determin cause of failure .Rebuilders don't care if you send a compresor back in pieces as long as the cover plates are on and it's not leaking oil .

[RichardL]

Good Grief!!!!!!!
Trying to set Suction Superheat on a TXV system by altering the Refrigerant charge is likened to controlling your trucks top speed by using the Emergency Brakes!!!

Assuming this is a 8 cyl. 2E compressor on a Trane water cooled condenser, it is terefore rated @ 100HP/85ton-ref.
Also the Trane condenser has within it a seperate chamber using the lower row of tubes within a boxed section to serve as the Sub-Cooler. Rated @ 15°f under rated conditions. The use of any reciever therefore is a mute point.(Reciever not required)
Since you stated it has 3 seperate Evaporator coils and is not a chiller, thecompressor should be equipped with the CNT-1 loader assembly which loads cylinders in pairs according to suction pressure.
On a DX system such as this it is normally set(adjusted) to haveall 8 Cyl. loaded @ Suction pressures over 62-65PSIG.
As far as the motor end-bell sweating, if it is not sweating to the end of the terminal box @ operating conditions your Suction Superheat is surely to high.
As tated earlier by others...Set the Head pressure controller to maintainthe required 100PSI MOPD on the TXV's, Charge for the proper Sub-Cooling, and Set the TXV's for the 12-15ºf required by the compressor rebuilder...
This ain't no refrigerator or water fountain!!!!!!!
Quit treating like one before you blow the damn heads off off it!!!

[sabre11134]

Sounds to me like they have a old built up system. most of the old k-marts with built up systems did not have any vav in the stores. With the three txv their were likely a step controller to control stages of cooling.To get in the fan room, you would have to brace one leg on the wall to pull open the door.I spent many years working on these type systems.

[heaviwall]

sporlan is very clear in there literature on minumum pressure drop across txv's head is abig problem here

[burner guy]

Amickracing.....

Trying to help your dad and trying to learn something in the process is very admirable, but please don't take it personally when I suggest: Get out!. What I mean is, it takes a strong man to acknowledge his limitations, and there is no shame in calling in help. From the sounds of it, your dad will be replacing this compressor under warranty in about 3 months. That's a very expensive lesson. "Pride commeth before a fall".

By the way, as far as I know, there are only two things (on the refrigerant side) that can kill a recip compressor: Low suction superheat(slugging), or high discharge temperature (oil breakdown).

Good luck, keep us posted.