PDA

View Full Version : Warm suction line, on a careful repaired machine.







AlexLPD
11-08-2015, 08:20 PM
Hi, first of all thanks for the comments.

Description of the system.-
This is a 3HP coppeland condensing unit running on a 5 fans low profile Bohn, evaporator. The TXV is a donfoss, the orifice was a #4. The unit uses a 3PH 3HP 220V compressor.

This is a bread cold room used to keep the bread before the baking. (Desire temperature from the costumer is 4-5C)

The unit burn out a compressor, the client contract some one else to change it... We arrive at the scene because the compressor, don't start... The reason a damage low pressure protection, after this, we check the refrigerant and was none on the system.


The work was done on the system.-

The following procedure was make in order to fix the condenser;

1.- Chargue 350Psi of N2 to search the leak
2.- A broken nut on the txv was the leak. we Changue it and make a new fitting.
3.- We changue the liquid filter for a new one.
4.- Add a suction filter to the low side of the compressor.
5.-Change the sight glass, were too dark.
6.- Re- test on 350Psi of N2... The system hold its.
7.- We make vacuum on both sides of the unit (Also energize the solenoid)
8.- Re fill the system with brand new R-22.
--Clean the condenser coil--

Now the problem being.-
The compressor runs very hot, the evap temp is very high.

The pressures was nearly ok, but wasn't any return of cold to the compressor on the suction side, the air depleted of the condenser is 40C, and the lowest temperature on the evaporator was around 11C... so... we play a litte bit with the refrigerant charge but nothing... After changing the #4 for the #5 orifice of the TXV.

Nothing happens to the head pressures, so... the metering device wasnt opening or closing, the same pressure on the beginning of the cycle (even the chiller was warm some like 20C) to the lowest temperature we can achive... (some near 14C)

So, I change the TXV for a brand new danfoss, and leave the #4 orifice, now we can see some variation of the suction pressure, around 55Psi on the beginning and 45 at the lowest temperature we can achive at the time (Around 11C on the out of the evap and 13 on the chiller).

The last data is;




REAL

REAL

CHART







PRESSURE

TEMP

TEMP






LOW SIDE
40
Psi
107
F
18
F
89
F
OVERHEATING


HIG SIDE
200
Psi
107
F
100
F
7
F
SUBCOOLING




So, the issue is a high overheating If i not made a lots of typos, but cheeking the list of the possible causes;

http://heatingandaircoolingrepairsdotcom.files.wordpress.com/2013/07/20130729-200951.jpg

Dont have a scenario when normal subcooling, higgh superheating, and normal low and high pressures.

Even so, the possibles scenarios are;

Low charge (The amp of the compressor is on the limit with 8.9A)
Low air flow on condenser ( Was clean recently)

Server restriction on with excess chargue (???)
Liquid refrigerant mild restriction. (????)

So, I might be looking for a bend on the liquid line and I have an overcharge...

Now I now many of you will need more data, I will provide as soon I can...
But for the sake of the tech visit, can you provide with some other possibles causes? or field experience?

Thanks a lot.

Kind Regards.
-Alex.

AlexLPD
12-08-2015, 02:39 AM
The specifc compresor is this
From techumsem http://www.tecumseh.com/en/United-States/Products/Reciprocating-Compressors/AVA5538EXT?fromsearch=1

So the rated running amps are 10.8.
I will try to add more refrigerante, to See if there is a changue.

cadwaladr
12-08-2015, 03:36 AM
Try to pump down the system by shutting receiver tank outlet.

AlexLPD
12-08-2015, 05:32 AM
Try to pump down the system by shutting receiver tank outlet.

Hi, and thanks for the reply.... Im not native english speaker, so pardon me if i ask again....

Do you mean close the liquid line and trap all te refrigerante on the reciever? I have to do this a couple of times while changing orifices... Was no improvee ... Im missing something here?

-Alex

cadwaladr
12-08-2015, 06:21 AM
It should pull a good vacuum you may have to bypass the low pressure switch to observe how deep a vacuum

AlexLPD
12-08-2015, 03:37 PM
So you think there is non condensables on the system... It will be odd but I will try it.. by removing the refrigerant and cheking if there is a major difference. Also check the pressure on the gass cylinder to see if there is non condensables.

Also, Im starting to suspect the soleoind valve may be flashing the liquid before the TXV. Will test some temperatures along the liquid line to see if there is something wrong.

Thanks.

Regards.
-Alex

AlexLPD
12-08-2015, 03:55 PM
This guy rigth here seems to have blew some sort or bliking on the liquid line with the nitrogen...
I wonder if I have to do the same....

https://www.youtube.com/watch?v=GbyX0wop72E

monkey spanners
12-08-2015, 07:45 PM
Had one where the defrost heaters were stuck on. System could never reach temperature.

AlexLPD
12-08-2015, 08:09 PM
Hope that was my case... evap is air defrost... But thanks for the reply!

Glenn Moore
12-08-2015, 11:13 PM
Have you adjusted the new expansion valve to reduce the superheat ?

AlexLPD
13-08-2015, 07:10 AM
Yes I tried the problem is very odd due to the pressures witch are in the range of; 40psi corresponding to -7.8C. Lets say a superheat of 6deg... Evaporator out will be something like -1C. Or 50psi corresponding to 3.8C with the same superheat will be around 9C on the warmest temperature... yet the evaporator mos cold was about 13C so the cold room was about to 14 to 16.

I try to adjust the valve on two oriffices the No.4 and the No. 5 was a very low improvement on the 4 from 16C to 13C of the evaporator output. I even think the evaporator was mismatched so I disconnect the center fan leaving only 4 fans to deplet air. This was the best set up and was the better and coldest setupt we can made at the time... Tomorrow I will try to bring more photos of the actual system.

Any other tougths?
Alex.

Martin Davies
13-08-2015, 08:05 AM
I would remove the refrigerant and try vaccing the system on 1 side to make sure the other side produces a vacuum. Then remove the suction filter and replace with new. This could be clogged with oil from the old compressor.

How long is the pipe run?

AlexLPD
13-08-2015, 02:14 PM
I would remove the refrigerant and try vaccing the system on 1 side to make sure the other side produces a vacuum. Then remove the suction filter and replace with new. This could be clogged with oil from the old compressor.

How long is the pipe run?
Hi, and thanks for the reply....

the compressor were changued for a thir person... Yet at the moment of the leak search was do... We put a brand new filter on liquid and one of suction. Still I will chek for any temperature difference to see if there is something wrong on thath ... The pipe run is minimum I can say for sure no longer than 10ft pr 3m... The condenser is right above the roof.

The most disturbing thing is the suction accumulator and the old suction filter shows cracked paint typically from low temperatures associated with a good and nice sweating pipe...

I will do a mos careful chek the next time I go there... And try to bring fresh data...
thanks a lot!!!

Alex.

AlexLPD
13-08-2015, 02:22 PM
Suddenly I got this weird idea.... The oil separator, has been on the system before this compressor and before the past compressor burn out (yes this systems has burn out three compressors thath I'm aware of) ...

if there is a chance of the oil separator to be installed empty at the beginning , or some how got low level of oil and its allowing to pass liquid plus very hot oil to the lines ?

Well... I guess I will have to take some extra temperature measurements.

kind Regards.
Alex

AlexLPD
16-08-2015, 05:28 PM
Hi to all again... The problem has been solved... I just brought the information in case some one else have a similar case.

So the only probable bloking on the system was the solenoid valve... so we remove it (glad it was a flare one) ..
https://oakitg.dm2301.livefilestore.com/y3pQ-4jHzhVQnsamelPlm0UB8tWOKm0GPCcpud3ZiENJySIXEyvdqVfr6XyCh3R2waHc14Xn3E3p93Jzk7t89tP36sy3aL4zRuGXumlpT N-0aQn1F4gAJJbrj5nUbGLTp1QqFDUPI7XofIz9kUcbQANVYZrVujLB16oNCA23ZOg_Dc/IMG_20150815_135506.jpg?psid=1

So after removing the solenoid the suction pipe star to feel a litte bit coolder.. we chek the pressure sets....and realized we need a litte bit more refrigerant.

We add it until we have a nice and interesting frosty pipe...

https://oakitg.dm2301.livefilestore.com/y3pU5PZ-C2HOGQtP3YHbRBAUTxkDZ-5q7H_pViPuMM4qZgZn8pXwgz3GY6d5aFw_5ZPzc5M_Nexmv4oB6pPmA6gNha3mx3SGbTd3BXlgd29ufPlfOwKHos07SqQOjcmbV4 686k54Q5DFqB_ZXr8We9um6jPnk6zJQdfExdMDGBpico/IMG_20150815_133825.jpg?psid=1

Know the sigth glass have a nice stream of liquid... (sorry the pic is no so clear)

https://oakitg.dm2301.livefilestore.com/y3pgrgaZfDFksgFRYRAYpQoWnVp59p8O7egtfxwBg7GeMv2sB0cQg2WHqh075AJouFUnBcP8ygxk3dY2uZ2HE9-LmgRNXMwctRumOSabU6kEkwxZsG7z4JsPLHsFX1oReHJ2NKDpS5XqAIYD6D-QqEbu3mz1cxBt6yzjUWyIPn5jvg/IMG_20150815_133821.jpg?psid=1

And finally we start to have a nice cold suction line...

https://oakitg.dm2301.livefilestore.com/y3p-d1HWdLYvkGeZfXfbYFJjud0EOjf4vRHWxy2iNcXg_xUnHwh1VCYBsE-uq2QH-TIBWzCUgvSJ02mYXVfyffdEEg_iBoytkgNzj0QKIU0mOpSZvQfIjDi0LmLn46XGGOLDxc3h7KRnIZW-8038FGz4722WwUAfPvoMNFSlZHGuHI/IMG_20150815_133732.jpg?psid=1

Finally.. a happy condenser at 40C not 52...

https://oakitg.dm2301.livefilestore.com/y3p6rTr2mpSTTGMEgLQ7RQOhNz63pygwOJ7awb6f_hCf2QvFePG2nrTvJ057pmaxs7ZsXaYi2zNCERZZltzvscssIMlHMblfkhjo 3OWN95BTN1qJ7kb_EKPt2E6j-jlaYXrmz8fdyZoxn5wohRsQrE-eCtSdFiAZ7uFjzF25yc4kRw/IMG_20150815_135550.jpg?psid=1


Well that's thats for know...

Thanks a lot.

-Alex.

Martin Davies
16-08-2015, 06:32 PM
You've removed the solenoid?

AlexLPD
16-08-2015, 07:24 PM
Yes yes, the main idea is to install a Danfoss If the client Agrees to...

For what I read the main problem on the refrigeration without solenoid... One is the chance of liquid condensating on the compressor ( I dont think this will be a problem, the unit is above the evaporator )

And the oil migration to the system, This system counts on a oil separator...

And for the liquid trapping... this system has the solenoid in parallel with the compressor contactor...


Any toughs?

-Alex.

Martin Davies
16-08-2015, 07:58 PM
So it's direct on direct off but had a solenoid in place too... Weird and pointless. I would install a new solenoid and have the comp on a pressure switch pump down. What sort of controller have you got?

AlexLPD
16-08-2015, 11:01 PM
Yes ... very pointless...

We have an electric control, I mean onyl NC and NO contacts... the low pressure, the high pressure, the thermostat, ...

A pump down to close the solenoid, and stop the compressor when the unit has trapped the almost of the liquid.

Interesting tougth.... You have any pics or diagrams?

Thanks.
-Alex.

Martin Davies
17-08-2015, 06:34 AM
It's just a basic control circuit but the brain is the controller so it depends what you are using as a controller in this set up?

Martin Davies
17-08-2015, 06:41 AM
13847

Very basic set up

AlexLPD
18-08-2015, 05:13 AM
So it all depends on the control ... As appears to me only 3 variables are needed for... An Arduino mini, two temperature probe and one single block of relay will do the trick... Even you can program the delay on compressor start.

danfoss will sell something like these but is not very common in here.

ok, I will try to bring a feasible solution in this days.

thnks a lot!
-Alex.

AlexLPD
18-08-2015, 03:32 PM
Well sorry for the skydrive malfunctioning... here are the attached files.

13852

Here is the partially clogged solenoid.

13850
After the removing of it... the chill star to moving t the compressor XD


13848
A nice and sweaty suction line.


13849
And a happy liquid flow to the evap


13851

Finally a Happy condenser at 42... no 52C

Kind Regarsa.
-Alex.

Martin Davies
18-08-2015, 04:28 PM
Not a piece of lagging in sight! That will definitely not help your cooling issues especially if it is hot where you are...?