super heat and overcharge help for a noob

[frostedflake]

greetings again RE forum

i'm still trying to understand the role of superheating and subcooling so far i think i understand the fact that too much or to low superheat are bad for the system as also subcooling.

i recently installed a brand new york minisplit 12,000btu model tlea12fs-adr, 5 mts piping (came default with unit)
installation went A o.k., i ran a vacuum test for 15 min to remove air from the evaporator pipings and no leak was detected after another 15 min of testing.

the unit works like a charm, below i list you the readings:

refrigerant r 22
amps 5.5 (plate amps read 6.6)
suction pressure at service valve at condenser 50psig
measured temperature after 20 min operating 8 ºC (superheat 5k?)
ambient temp 27ºC condenser air temp 35ºC
i can't provide discharge data cause there's no service valve available for discharge.
indoor evaporator air temp 12 ºC

my concern came when i removed my manifold and realized that some foaming oil came out.

is foaming oil the result of the fact that this york unit says being charged from factory for a piping of 7 meters and me only using 5? do this mean i might have some liquid going to the suction?

is my superheat value ok?
how do i take te subcooling when i have no service valve?
i was wrong taught to calibrate this systems by amperage but now that i'm undestanding superheat and supercooling i'm somewhat puzzled...

low amps for me meant: low charge (which cannot be the case since this unit was factory packed with enough refrigerant for 7 mts instalation (according to installation manual).
however the low suction pressure and the superheat might tell you experts something i am missing

thanks so much in advance

[amitsaxena]

Hi,

What i feel is
1. As you have reduced the length of piping, hence the system is behaving like overly charged.
2. Initially when you run the system then some of the OIL comes from comp to Eva side as this is called as flooded start for the comp. This happens because the initial load is less and also the system is overly charged hence possibility of some oil accumulation in suction.

Thanks, and reply if you find my answer logically true.

[RUSTY]

Hi, 7metres is most likely the maximum you could run with out adding more refrigerant, sounds like you lost a small amount of gas, in future you could pump your guages down by shuting the suction service. 410A ?

[nike123]

greetings again RE forum

i'm still trying to understand the role of superheating and subcooling so far i think i understand the fact that too much or to low superheat are bad for the system as also subcooling.


Condenser subcooling tell us what portion of condenser is filled with liquid refrigerant (subcooled beyond point of SCT). If it is excessive we know that refrigerant is accumulated there because of some restriction in high side, or because of over condensing, or because of overcharge. If it is low, we know that there is not enough refrigerant in there or heat is not dissipated enough from condenser. Total subcooling tell us if we have or don't have liquid refrigerant before expansion device and that is important for proper function of expansion device.

Evaporator superheat tell us what portion of evaporator is filled with fully evaporated refrigerant and what is his efficiency. If it is low then it could be low load or to much refrigerant from expansion device. If it is high it could be high load, low air flow or shortage of refrigerant (either because of expansion device or lack of refrigerant charge).Total superheat at compressor tells us if we have enough superheat to avoid occurrence of liquid refrigerant in compressor.



i recently installed a brand new york minisplit 12,000btu model tlea12fs-adr, 5 mts piping (came default with unit)
installation went A o.k., i ran a vacuum test for 15 min to remove air from the evaporator pipings and no leak was detected after another 15 min of testing.Clarify this!
Did you run vacuum pump for 15min and then isolated it at manifolds and then checked for rise in pressure at gauges for another 15 min.

Above presented is comon practise in "take money and run" buisnesses. :(
Proper procedure after commissioning is to to make pressure test with nitrogen, and after pressure test, evacuation to 500 microns (checked by electronic vacuum meter connected at furthest point in system from vacuum pump) no matter what time is needed to achieve that vacuum level. Then check is done with same vacuum meter when vacuum pump is isolated that pressure doesn't rise more than 1000 microns and stays stable at that level which shows us that there is no more moisture that evaporates in system.


http://farm4.static.flickr.com/3030/2817747757_0dc0d6b752_o_d.jpg

I don't know your location, but above procedure is mandatory in EU. Still, I personally found it excessively time consuming and to expensive for my country, which is not part of EU jet. Therefore, I have shortened it by spiking nitrogen leak test (only for domestic ductless split systems of lower capacity without welded joints) and leaning at leak test by vacuum meter, and later after starting unit in heat mode, I double check by soap solution at flares. It is much cheaper (customer friendlier) and faster.


the unit works like a charm, below i list you the readings:

refrigerant r 22
amps 5.5 (plate amps read 6.6)
suction pressure at service valve at condenser 50psig

measured temperature after 20 min operating 8 ºC

(superheat 5k?)
ambient temp 27ºC condenser air temp 35ºC
i can't provide discharge data cause there's no service valve available for discharge.
indoor evaporator air temp 12 ºCWhen you measured that pressure, at what speed was fan? Where did you read that 8°C?
How you got 5K superheat?

50 psig is -4°C for R22, and if pipe temperature at suction valve is 8°C, than your total superheat is 11K.



my concern came when i removed my manifold and realized that some foaming oil came out.

is foaming oil the result of the fact that this york unit says being charged from factory for a piping of 7 meters and me only using 5? do this mean i might have some liquid going to the suction?
That is normal, especially after opening service valves when oil is rushed out together with refrigerant.




is my superheat value ok?That depend on how are you came to that value. If it is correct value than regarding at compressor health that value is good but regarding at charge amount that depend on expansion device used.
If it is TXV than you need to check charge by subcooling. If it is orifice or capillary tube, than you need to consult charging chart of manufacturer, or weigh in charge.


how do i take te subcooling when i have no service valve?Check in housing that you maybe have access valve inside. If not, then you cannot measure discharge pressure. You could only measure temperatures of pipes at middle of condenser and at condenser outlet to get subcooling.


i was wrong taught to calibrate this systems by amperage but now that i'm undestanding superheat and supercooling i'm somewhat puzzled...Yep its wrong, calibrate it (charge) by correct refrigerant weight. Recover and weigh in correct amount!


low amps for me meant: low charge (which cannot be the case since this unit was factory packed with enough refrigerant for 7 mts instalation (according to installation manual).Low amperage mean low compression ratio. That also could be because of low outdoor temperature or low indoor load. Rated current stated on unit is when outdoor and indoor temperatures are at test condition stated in technical data (usually indoor air at 27°C DB and 19°WB and outdoor air at 35°C DB and 24°C WB by ISO-T1 standard). Or, sometimes it could be FLA stated.


however the low suction pressure and the superheat might tell you experts something i am missingFirst confirm that readings are taken when indoor fan is at maximum. Since this is old unit (r22 inside) also check that evaporator and filters are clean.
Or is it possible that it is new unit with R22. That would be crazy in this part of world.

[frostedflake]

thanks for the quick reply amitsaxena much appreciated.

as for your reamarks:

1.-I agree with the reasoning that 7 mt piping refrigerant calculation will behave like an overcharge inside a 5 mt installation (we both see the logic there right?) however that does not explain the low compression ratio i get traduced as a lower than plate rated amperage.
2.-I think i get now what you explain about the oil, as it is normal for it to travel along with the refrigerant all over the system, so now do you suggest that i should recover some refrigerant to even the system capacity performance and avoid liquid flooding back to compressor?

best regards

[frostedflake]

Thanks Rusty

For what I read in the York AC manual, there should be some refrigerant added indeed if the 7mts are exceeded, i now wonder what is the procedure/method when you shorten the piping length (from 7mts to 5 mts).
I very thoroughly checked the piping for leaks, none found (steady suction pressure after system stabilization), and btw the refrigerant is R22.

take care

[frostedflake]

Greetings Nike123

Thanks for your always extensive and clear replies.

i'll try to reply in order according to your remarks:

For the superheat and subcooling understanding, with what you explain here, plus the many other posts in this forum about that particular subject I have now lots of references and all of them very useful. thanks

Now, about my leak/vacuum testing methods, I run the vacuum test with my manifold conected to the service valve (low side) and check my readings in mercury inches (Hg IN), if i reach the 30hg within some time period (depending on pipe size/length) then i proceed to another 15-20 min vacuum, turn off then vacuum pump and wait some other 15 minto see any changes in manifold.

I do understand the first world hvacr obligatory standards and i am aware of the use of nitrogen for pressure test and clean soldering/welding, but i pressure test with some refrigerant, in this case some r22 (depending on pipe size length and system refrigerent of course) up to 110-120 psi, then apply the always useful and indeed user friendly soapy water to check for bubbles and check my manifold for any pressure change, then i recover the used refrigerant and proceed to open condenser valves to start the system.
I have no intention on building a "take money and run bussiness" and i do admit my procedures come from the lack of knowledge, however I'm always looking to improve, so i'm getting myself a nitrogen tank and a micron gauge to use from now on.

Talking now about my 5K superheat reading, the way I got it is that after refrigerant passes through the evaporator (hence gaining heat) up to the service valve at condenser where i measured suction temp over copper piping with type k thermometer, and after 20 min of system working with evap fan at high speed and 21ºc remote control temp, then i read some 8ºC at 50.5 psi, then looking to my sporlan pocket P-t chart i see that 50.3 psi of R22 refrigerant equal a -3ºC temp, so i do the following:

8
+
(-3)
---------
5K superheat

however if my method is wrong and i should substract instead of adding then i see the superheat of 11k, hence meaning that now i have a high superheat and a low suction pressure.

which does not make much sense to me, because if that were the case then i should have lower superheat because of the factory charge excess refrigerant for the 7mts vs actual 5 mts piping right?

i read that some 5 to 10 superheat is allowed for air conditioning depending on the expansion device used, in my case this is a capilary tube system with no txv installed.


thanks for taking the time to read this post and have a good day

[nike123]

Now, about my leak/vacuum testing methods, I run the vacuum test with my manifold conected to the service valve (low side) and check my readings in mercury inches (Hg IN), if i reach the 30hg within some time period (depending on pipe size/length) then i proceed to another 15-20 min vacuum, turn off then vacuum pump and wait some other 15 minto see any changes in manifold.

I do understand the first world hvacr obligatory standards and i am aware of the use of nitrogen for pressure test and clean soldering/welding, but i pressure test with some refrigerant, in this case some r22 (depending on pipe size length and system refrigerent of course) up to 110-120 psi, then apply the always useful and indeed user friendly soapy water to check for bubbles and check my manifold for any pressure change, then i recover the used refrigerant and proceed to open condenser valves to start the system.
I have no intention on building a "take money and run bussiness" and i do admit my procedures come from the lack of knowledge, however I'm always looking to improve, so i'm getting myself a nitrogen tank and a micron gauge to use from now on.

Good, I am glad if I contributed to that.


Talking now about my 5K superheat reading, the way I got it is that after refrigerant passes through the evaporator (hence gaining heat) up to the service valve at condenser where i measured suction temp over copper piping with type k thermometer, and after 20 min of system working with evap fan at high speed and 21ºc remote control temp, then i read some 8ºC at 50.5 psi, then looking to my sporlan pocket P-t chart i see that 50.3 psi of R22 refrigerant equal a -3ºC temp, so i do the following:

8
+
(-3)
---------
5K superheat

however if my method is wrong and i should substract instead of adding then i see the superheat of 11k, hence meaning that now i have a high superheat and a low suction pressure.

Your math is wrong. You are calculating temperature interval. That is from 8°C to 0°C is 8K and from 0°C to 3°C is 3K and that summed gives 11K.


which does not make much sense to me, because if that were the case then i should have lower superheat because of the factory charge excess refrigerant for the 7mts vs actual 5 mts piping right?

i read that some 5 to 10 superheat is allowed for air conditioning depending on the expansion device used, in my case this is a capilary tube system with no txv installed.


11K superheat doesnt necesary mean that is high. You should find charging chart of manufacturer and compare that with your reading to evaluate if superheat of 11K is high or normal for given conditions (indoor and outdoor DB and WB temperature).
If you dont have one you could use generic chart.

http://farm4.static.flickr.com/3492/3270339104_da4f032eba_o_d.png

Pressures in table are absolute and high efficiency table is for 13SEER and higher!
According to this table, your pipe temperature is 2K higher than in high efficiency, and 3K lower than in low efficiency table, and I would not touch charge.

[amitsaxena]

Dear, Thanks for your reply,

Yes the better way to rectify the problem is remove some qty of the ref. from the unit, as it will reduce the flow of OIL with Ref in the system.

Thanks

[frostedflake]

Thanks so much for your replies, i'm looking forward to reciprocate the help i just recieved!!

have a great day

[Slatts]

I've seen frostedflakes maths system used by a number of people over the years.
It seems to be a fairly common misconception.
Just to reinforce what nike said:
-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8
___1_ 2_ 3_ 4_5_6_7 _8_9 10 11
eg; the difference between -3 and 8 is 11
Does that help clarify the arithmetic?

[frostedflake]

yup my bad, so much for doing addition rather than substraction

i now have a pocket calculator and an abacus if all else fails lol