one for the experrts (liquid line condensing)

[frostedflake]

greetings RE forum!

i bring to you this unit that has troubled me for my lack of knowledge on the field...(i'm doing lots of homework but still) :o

it is a carrier mini split model (located at condenser unit because evaporator had no data anywhere, not even pcb diagram sticker)
38xca12226-c 12,000BTU's R22 220v 60 hz 3517 W 6amps.

and here the pressures/temps (hope i got them right)
SUCTION pressure at shearer valve at condenser:
60 psi (4.13 bar), measured temperature with type k thermometer located over condensing copper pipe and got a 12C (53F) reading, so i think i have a 9 k superheat.

this condenser unit has no service port for liquid line to evaporator so i only took temperature readings at shaerer valve (16C/60F and condensing on a less than 5mt/15ftinstallation) and a temp of 42C/107F on the condenser air outlet(on a 30C/107F day and with RH at 70%).

as for the evap unit:
room temp 27C/80F and evap air outlet temp is from 15C/59F at start and 12C/53F after 10-15 min operation, and the temp at the entrance of the evap (where a copper bullet goes from there to PCB) is 8C/46C.

here's the background:
no service whatsoever to the unit and over 6 years of use (i know that's a lot), recently cleaned evap and condenser so both got proper air flow, can't measure cfm but there seemed to be a problem with the evaporator motor (it started ok but then rotated very slowly), so i checked the evap fan capacitor and yes the cap was defective, replaced with exact same type cap and evap fan worked fine, however i don't understand the condensation on the liquid line, and the fact that the evaporator turns to fan only after only 10 to 15 min operation, i checked also on the pcb the ohm values for the temp sensors both the one in the front of the grill and the one direct to the copper pipe at the evaporator they seem to be within ohm range.

hope you can give me a little push on this one because is tricking me a lot

thanks in advance!
:)

[nike123]

however i don't understand the condensation on the liquid line, and the fact that the evaporator turns to fan only after only 10 to 15 min operation, i checked also on the pcb the ohm values for the temp sensors both the one in the front of the grill and the one direct to the copper pipe at the evaporator they seem to be within ohm range.

:)

What you are referring here is not actually liquid line. Since expansion device is in outdoor unit, that line is after expansion device, and sort of start of evaporator, therefore condensation on the line if not properly insulated.

"Evaporator turns to fan only" probably mean that evaporator heat exchanger is too cold and unit goes to frost protection mode.
That could be because of insufficient air flow or low refrigerant charge or some restriction in capillary or simmilar.
If you are sure that you have required air flow (although that could be the case only after you make measuring of flow) recover refrigerant and measure his weight to establish if it is short of refrigerant or you have restriction.

[frostedflake]

thanks for your quick response Nike123. :)

i am inclined to the possibility of a restriction on the capillary tubes (at evap) because of a sudden "unclugging sound" when i was measuring the evap pcb, and after that the evap worked fine, however i am concerned with the possibility that the system still has a high superheat.

the evap switching to air only mode was (i think) because of a small wall (cubicle wall) in front of the evap so that might trick the sensors and therefore turns off the compressor.

so if customer agrees, then i should recover refrigerant and weight it to be certain of the correct charge/obstruction.
then i should also make a cleansing of the system?
and what is a propper superheat value for this unit?
my calculations is no more than 4 to 6 K because it is not a txv system.

thanks again and have a good day.

[nike123]

i am inclined to the possibility of a restriction on the capillary tubes (at evap) because of a sudden "unclugging sound" when i was measuring the evap pcb, and after that the evap worked fine, however i am concerned with the possibility that the system still has a high superheat.


There is no capillary tube at evaporator, as I said earlier, capillary is in outdoor unit. Sudden unclogging sound could be if 4-way valve is acted for some reason. Check connection cables. Also, comes to my mind, when I read that, that 4 way valve could somehow be a problem. So, inspect his correct function and temperature drops at valve.


the evap switching to air only mode was (i think) because of a small wall (cubicle wall) in front of the evap so that might trick the sensors and therefore turns off the compressor.That could be the issue. We call it air short cycling. That need to be resolved.



so if customer agrees, then i should recover refrigerant and weight it to be certain of the correct charge/obstruction.
then i should also make a cleansing of the system?First thing should be cleaning of heat exchangers (outdoor and indoor). That could resolve all problems.


and what is a propper superheat value for this unit?
my calculations is no more than 4 to 6 K because it is not a txv system.You could find expected superheat value (if charge is correct) , for orientation, by using this table.

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


Your unit is 10 SEER so you should refer to standard efficiency chart. Pressures are for R22 so you need to convert that to saturation temperature for other refrigerants.

[frostedflake]

thanks for the table and the quick response, i appreciate. :)

the cleaning of both evap and cond units was the first thing i did since the air flow was not the appropiate one. the additional cleansing i was reffering to was inside the system if an obstruction caused by dirt or humidity (non condensables?) could be the cause besides the evap fan cap replacement.
i opened the cond unit and evap unit to check for txv's, i found none, i only found on both units really thin copper tubes (at the inlet of the evap and the outlet of the condenser) so i think this system is a capillary tube controlled one.

the client is not ok with me recovering the refrigerant in the system to check the correct amount of charge (i am only charging the refrigerant $$ needed and nothing else), client says its not needed since evap is cooling and anything else beyond the cleaning of the evap and condenser is expensive so well...i think i'm out of this one u.u


:off topic: hvala, Jedan jezik nikad nije dovoljan, laku noc