Oil Logged??

[bernie]

I got this commercial split, with (tan) trane scroll compressor. R-22, Air conditioning application.
condenser has a reciever, solenoid, evaps are fitted with T.E.V.'s
Suction line has a sporlan removable core setup on the roof.
Evaporator is below the compressor, blower draws thru the coil.
88F ambient today.
Suction @ 50 and pulls down in the neighborhood of 20- 30
Suction temp at evap 32F + or - 2F @ lowest pressure.
Head pressure @ 205F
liquid temp at evaporator 100F
Distributor tubes all sweating and suction line starts to freeze as it exits the evaporator all the way back to the compressor.
Pulled core on drier for suction line, TON of oil present,
Core saturated with oil.
No appreciable pressure changes. I suspect, (due to their
is no suction riser trap, instead the pipe drops down, goes horizantal about 2 feet and then 6-10" up to the evaporator)
that evap is full of oil) the evap is full of oil. This would render the evap useless, and inturn the liquid dosent drop in pressure untill it reaches the suction line. This would explain the frosting back to the compressor.
So, our suction line is now the evaporator. Am I crazy or what?
Thanks Bernie

[bernie]

after reading my post, I vote crazy!

[condenseddave]

Originally posted by bernie
after reading my post, I vote crazy!

Post a poll, TT, we'll all vote.:D

[herefishy]

My first thought was that the system is undercharged.

Has there been a compressor change out or two on this unit? The excess oil in the lines could be there because of not enough mass flow (I.E. undercharge speculation), but if a couple of compressors have been in and out of the system, perhaps you have an excess of oil in the system.

I have had jobs that I walk into, first visit, and all the dead soldiers (replaced compressors) are still lying next to the CU. I've pulled the existing locked rotor compressor, poured the oil out of the compressor shell (hermetic), recharged oil and recommissioned. No prob.

[frank]

I've got to agree with the Fish. With a head pressure at 205psig at 88 deg F it certainly smacks of refrigerant shortage - or refrigerant blockage.

Frank

[bernie]

Well I drilled a hole in the suction line down at the evaporator, No oil was present. Put some access fittings on both liquid and suction lines.
Installed new core and evac system.
Start system
suction pressure @ evaporator 65psi
suction pressure @ evaporator fell to 54psi and Suction temp @ evaporator fell to 32-33F. Suction line icing on the roof.
Had a set a guages installed on the roof also.
Suction pressure @43psi, 11 psi drop does not seems right.
head pressure with one fan running @ condensing unit 250psi.
Liquid temp @ outlet of reciever 110F
So I've got near 0 superheat and low suction pressure.
Airflow is good. Compressor is rated @ 10 tons.
Expansion valve is rated @ 10 tons
Suction line size is 1 1/8" If my math is right that line is good up to 75000 btus @ +35F evaporator.
I should have 1-3/8" up to 60 linear feet, rated @ 120,000 btus
@+35F evaporator.
Would this cause my large pressure drop and susequent low pressure?
I have ruled out the expansion valve as being the problem.
This is all I have left to go on.
Thanks
Bernie

[herefishy]

"0" superheat?... Have you tinkered with you TEV setting? See if it responds. Furthermore, check the TEV nomenclature and make sure it's right.

I'd be cranking that TEV adjustment stem in, crack out ot the box.

[bernie]

Originally posted by herefishy
"0" superheat?... Have you tinkered with you TEV setting? See if it responds. Furthermore, check the TEV nomenclature and make sure it's right.

I'd be cranking that TEV adjustment stem in, crack out ot the box.
Hey Fish,
Its been a long day,
No i have not tinkered with the adjustment on the valve.
Do we agree that the valve is wide open?
Do we agree that I should have a higher suction pressure, providing everything else is in order?
Can we say that this suction line being undersized will cause this pressure drop? Is this pressure drop amount normal, I've never had to measure P.D. on the suction line.
Do we agree If I throttle that adjustment to a more closed position my suction pressure will decrease also?
Is the compressor sucking the suction line dry so to speak?
The only thing I haven't verified is the nozzle size in the distributor.
Thanks,
Bernie

[Gary]

My first thought is not enough info.

My second thought is not enough airflow, but I'm just guessing due to my first thought.

[bernie]

Hey gary,
Can you comment on the suction lines size?
How about the the pressure drop concern?
I have limited access to this problem ans Im supplying all the information I can @ this time.
Bernie

[Gary]

First we need to confirm airflow. "Airflow is good" doesn't tell me anything. What are the evap air in and evap air out temps?

[Gary]

Can you comment on the suction lines size?
How about the the pressure drop concern?


Lose the suction core. If the suction line size is borderline, then a suction drier just makes it worse, right?

You are assuming the system has a problem. It could have two problems... or three... or ten.

[Gary]

Let's imagine the scenario:

The installing contractor saves a few bucks by going very tight on ductwork and line sizes.

Along comes the service tech who notices the low suction pressure, so he dumps lots of extra refrigerant in the system. The compressor has a hernia when hot weather comes along.

The compressor is replaced and a suction drier is installed in a suction line that is already borderline at best.

Along comes another service tech who notices the low suction pressure, so he opens up the TXV setting.

If three people worked on it, then it probably has three problems. If five people worked on it, then it probably has five things wrong with it.

[condenseddave]

Gary's cup is always half empty...

But I tend to agree on the "lose the suction core" sentiment.

And what is the airflow, too?

[bernie]

I have no excuse for not taking a T,D across the coil.
When we got there today, I was told to stand under the register in the ceiling, you could feel the air blasting out. Granted this dosent ensure you have the necessary cfm
for proper operation but it was good enough for my boss as he was there and was insistant air flow wasn't the problem.
I should have taken a T.D.
As far as the valve goes I have zero superheat so I can
say its definately feeding enough liquid.
Look the way I see it I'm Screwed for not insisting on investigating the air flow issue further. This is basic stuff and its kicking our asses all over the place cause steps are being overlooked. The guy I work for is a very sharp technician. Gran ted he's no expert when it comes to refrigerant flow issues, he's your ddc and control expert
to some degree.
I'll be there again monday morning and the first thing I'm going to do is check the T.D.
I expect the T.D. to be in the 15-20F range.
This unit was installed in 99 and has always iced up.
This is a pomoma air condenser with trane 3d scrolls in them

[Gary]

Gary's cup is always half empty...


Sometimes more than half. Or is that less than half? :D

[Gary]

Okay, let's work it backwards:

The pressure at the coil is low @54psig.

When you remove the suction core, that pressure will drop.

When you increase the TXV superheat that pressure will drop some more.

If the subcooling is then high, you will need to remove refrigerant. This would drop the pressure even more.

With the refrigerant side all working properly, why is the coil pressure extremely low?

It all comes back to airflow. A 7 ton load for a 10 ton unit.

If you have a performance chart for that compressor, see how many BTU's it is pumping @ 43psig/20F SST. I bet I'm not far off at 7 tons.

[Andy]

Hi Bernie:)
I have see loads of suction/evaporator pressure readings, waht about the head pressure:confused:
What about the liquid temperature leaving the receiver:confused:
These will all effect the duty of the condensing unit and the system balance.
If you condenser is working in low ambient or below design ambient you effectivly increase its capacity until the cond unit is too large for the evap unit.
Also with reduced heads you will have reduced TXV capacity and poor refrigerant distribution at the evaporator, you may have a wide open TXV flooding a few of the evap circuits, but not enough for any decent evaporator duty, causing a knock on effect, where the compressor is not doing anything like it's design duty.
Moral of the story, more measurements required:eek:
Regards. Andy:)

[Gary]

Input. We need input. :D

In order to get this system right, we will have to peel back layers of incompetence. And this is typical. Sad, but true.

While we are on the subject and I am in the mood, here is another emperor-has-no-clothes type statement that everyone will hate:

Customers are better off without service contracts, because their systems will not fall prey to one incompetent service tech after another screwing them up.

I don't blame the service techs for this. When it comes to trouble shooting, refrigeration schools in general, and textbooks in particular, just absolutely suck. Schools teach the guessing game, and the powers that be think its the right way to do things. The guessing game is so deeply entrenched that it may never go away.

I have spent most of my adult life trying to change this. It is an uphill battle all the way, one service tech at a time, and the hard part is unteaching them the crap they learned in school.

Aside from that, I like the refrigeration schools just fine. :D

[Dan]

ZR108KC-TF5: At 120 deg F SCT and 45 deg F SST: 11,500 btu/hr.

At 120 deg F SCT and 20 SST: 69,000 btu/hr.

Using 65 deg F return gas temperature.

More like 5 tons.

[Gary]

Ouch. I stand corrected. It's worse than I thought.

Thanks, Dan. :D

[bernie]

I'll have all the required info and the solution to my problem on monday.
I do not believe in short cuts, and I have been quite humbled by this post.
I hope to redeem myself this coming week, and then we can have an intelligent discussion.
Bernie

[FreezerGeezer]

Bernie, could you tell us the model & serial no. of the unit? Also, how long is the pipe run, and how high are the risers?
Personally, I suspect that you may need suction riser traps, especially with that drier core.
In fact, I'm wondering why it has a suction drier? Trane never fit them in the U.K, unless it's to clean out a burned out system. And then they're removed once the system is clean. If the States do things the same way, then Herefishy is almost certainly correct - it wouldn't be the first time someone has overcharged a split with oil!
If the unit were short of refrigerant, then I would expect that the coil would ice up over the first part of it's surface. I doubt that it's really seriously short of refrigerant, as you say that the suction line is frosting over - sounds like liquid flooding back. I'm definitely becoming concerned about the presence of the drier.

You say that the suction pipe is frosting back all the way from the coil? Is it lagged? Obviously that's not the problem, but if it isn't, or the lagging is old & worn out, then there's a good opportunity to add some profit by correcting that!

[Gary]

I do not belive in short cuts, and I have been quite humbled by this post.


There is no need to feel humbled, and I hope you don't take my rantings personally, Bernie. They were not directed at you. You acquired and provided far more information than most, and recognized that steps had been missed. You are far ahead of the game.

[bernie]

Originally posted by Gary
There is no need to feel humbled, and I hope you don't take my rantings personally, Bernie. They were not directed at you. You acquired and provided far more information than most, and recognized that steps had been missed. You are far ahead of the game.

Not at all Gary, Thanks
Bernie

[bernie]

3

[bernie]

Air handler hangs horizantal.
Manufactured by L.J.Wing
IFB STEADYAiR II
S# 96-63590
TAG# SAS 115 HRS
COIL SPEC C-42-DS(I think this is for the steam coil)
2 DX coils stacked each with 10 ton sporlan valves.
Condenser is manufactured by Pamona Air
No Tag on unit.
Unit has 2 Trane 3-D scroll compressor's rated @ 10 tons each. (suction line @1-1/8")
Best guess on pipe run is 40 - 50 feet.
Single story structure so riser is 6- 8 feet at best.
Refrigerant lines drop down and travel underneath the air handler and the up to the coils. One big trap!!
I sent an email to the service department at L.J. Wing
and requested the specs for the unit . I'd bet those evaps are 6-7.5 tons each.
Those suction core driers seems to be existing from the old unit,
as this was installed in 1999. If the coils tuned out to be less than 10 tons I'll be yanking them.
Monday should be a pretty informative day!
Bernie

[herefishy]

In RE: the statement, "If I incresed the TEV superheat setting, my suction would decrease", well yes, except I anticipate the valve overfeeding, and the system undercharged. So when the superheat gets near right, you'll be adding gas.

.... just my two cents, because I wouldn't be satisfied with anything until the TEV got tampered with. "0" superheat..... good grief.

[Gary]

On the contrary, zero superheat tells us there is more than enough refrigerant to completely flood the coil. When we increase the superheat (reducing the flow) that excess will back up towards the condenser, and the system may very well be overcharged. It is definitely not undercharged.

[bernie]

Get some coffe this will be long winded.
Upon arrival verified cfm discharge at 4000 + or - 200cfm.
Used elnor hoper style instrument to meausre.
Recieved email from L.J wing and that unit is rated for 4300 cfm's.
As stated befor this unit has 2 dx coils not supplied by L.J. wing
Each distributor is 5/8 I.D. with 5 - 1/4" distributor tubes @ 12"
long each. Nozzle is a #6.
Using the sporaln guide , This set up will handle 5.75 tons per circuit.
As stated earlier each circuit now has a 10 ton compressor.
We now know the reason for the 0F superheat and the low suction pressure.

Someone got their math wrong in 1999. So with a limited budget
we proposed to remedy the situation in this manner.
First, one compressor will sit idle as it will not be needed.
A new 1-3/8 suction header will be added on the roof attached to the 1 - 10 ton compressor. Each 1-1/8" existing suction line from each circuit will the piped back to our suction manifold.
the old sporlan drier shells will be removed and a new properly sized shell for the 10 ton load will be installed on the 1-3/8 manifold.
Ditto for the liquid side of the system.
Each circuit at the evaporator will be fitted with 5 ton Q - valves
and a number 4 nozzle (or 5 I have to double check). In addition a liquid site glass will also be added.
As it stands now, control of system will remain the same and a call for cooling will deliver the full 10 tons available.
If required later, solenoid valve and hotgas discharge valve will be added for 2 stage operation and capacity control. Liquid injection if required , can also be added if proves necessary.
I'll breath now and respectfully ask for comments.
Thanks Bernie

[Gary]

:D

[Gary]

If you have a performance chart for that compressor, see how many BTU's it is pumping @ 43psig/20F SST.


At 120 deg F SCT and 20 SST: 69,000 btu/hr.



Using the sporaln guide , This set up will handle 5.75 tons per circuit.


69.000 btu/hr = 5.75 tons

Pretty close, Dan. :D

[Prof Sporlan]

So its the old two 5 ton evaporator coils connected to two 10 ton compressor trick... :D

The 1-1/8" OD suction lines should be ok to get oil back to the (one) compressor.


Each circuit at the evaporator will be fitted with 5 ton Q - valves
and a number 4 nozzle (or 5 I have to double check).
A #4 nozzle is fine for a 5 ton R-22 a/c load. Our SVE-5-GA may prove easier to install than the EQ valve with the 5 ton cartridge, since you will be replacing OVE-10s.

[bernie]

Im getting old,
Not sure if I ever did what I said I was gonna do!!!!
I miss these kinds of issues.
Hope everyone is well.
Bernie