appears short of refrigerant

[TECH TIM]

i have been out to replace a compressor in a unusual display cabinet and im saying unusual as i hardly see much commercial any way the unit is approx 4 meters long in display area the evap runs the length of cabinet it is a horizontal evap 2 tube high and 6 tubes wide the uint has storage underneath with an evap also rinning the length of cabinet and its a vertical evap 1 tube wide and 2 tubes high both evaps are static cooled(no evap fans) both evaps have a tx valve it has 7 doors to under bench storage area there is no manuaf info on cabinet i can see,
The compressor i replaced around 3 months ago it seemed to be going ok and i was called back next day as was not cold enough, a little more refrigerant and off i went, i called the day after and coil was flooded temps were good and off i went all was good until today i was called and found sight glass bubbles and top evap runnin short ie first run only half flooded at this stage i only had suction line attached and pressure was 310kpa (43psi) due to the bubbles in sight glass i added a little fefrigerant and found no change in suct press or evap flooding in total i added approx 200 grms and found no change in evap or pressure, the system appears to run extremly hot and i then placed my gauge on liquid line i found i had HS press of 3300kpa (475psi) and still LS 310kpa(43psi) i turned system off and allowed pressures to equalise and found appeared ok i the restarted unit after 10min or so off and found same pressures the condensor is slightly blocked you can see some dust in there but you can see through it i am returning to throughly clean condensor but i am wondering if anyone may have some tips for me as correctly diagnose differences between short of gas symptons and blockage symptons this is proberly a very silly question but i gotta ask thanks for taking the time to read my story i hope to hear from you cheers

[TECH TIM]

oh i forgot to mention the compressor is a kirby(heatcraft)type and manuf no. aw54lz-1c system operates on r22 how easy to forget the most valuable information

[piersons_man]

Hi Tech_Tim

does the unit have a reciever?
was the drier changed and unit fully evacuated when the compressor was changed?
silly question but is the condensor fan goin? :confused:
what sorta superheat are you getting on the evaps?

for r22 310kpa is around -6C for static coils you should expect around -10 to -12 from my experience

475psi is crazy! no hp switch i gather? be careful!

cheers

[TECH TIM]

YEH NO HP i a bit worried bout that i was gettin suct as low as 275 wich on gauge says -10 i havnt gone as far as checkin superheat not too familuar wit that both evaps join into same suction line wich is prob normal system has got a reciever and dryer was chenged with compressor and unit was fully evaced cond fan all ok im not to sure with super heat should i get suction press at comp and suct line temp at evap ?? any tips would be great thanks for takin time to reply also temps in bottom compartment are roud 5-6 deg cel but in top (where evap not flooded) temps round 16-20 deg cel i dont wanna put more gas in even though sight glass bubbles dont want head press to get any higher (if thats poss)

[nike123]

YEH NO HP i a bit worried bout that i was gettin suct as low as 275 wich on gauge says -10 i havnt gone as far as checkin superheat not too familuar wit that both evaps join into same suction line wich is prob normal system has got a reciever and dryer was chenged with compressor and unit was fully evaced cond fan all ok im not to sure with super heat should i get suction press at comp and suct line temp at evap ?? any tips would be great thanks for takin time to reply also temps in bottom compartment are roud 5-6 deg cel but in top (where evap not flooded) temps round 16-20 deg cel i dont wanna put more gas in even though sight glass bubbles dont want head press to get any higher (if thats poss)

First thing to do is, to clean that condenser coil, and be sure that fan is working properly.

Than measure temperature of pipe exiting condenser and subtract that from value of saturation condensation temperature from high pressure gauge (or convert it from high side pressure). That will give you subcooling value, which tell us state of refrigerant charge in system with TXV valves.
If it is higher tan 8K, remove some refrigerant until subcooling is lower than 8K and still above 3-4K (allow some time of 15-20 min between readings), and than make again readings of system pressures and temperatures:



Suction pressure
Condensation pressure
Display cabinet temperature
Air temperature in and out at condenser
Temperature of pipe at exit of evaporator
Temperature of pipe at suction on compressor (15-20 cm from compressor)
Temperature of pipe at exit of compressor
Temperature of pipe at exit of condenser
Temperature of pipe at entrance of dryer
Temperature of pipe before TXV


Make temperature readings with accurate thermometer suitable for pipe temperature measurements.
And, please, format text to be readable. You have 28 year and degree. I assume that you should know how to properly format your sentences.

[TECH TIM]

Hi Nike, thanks for the comment on my gramma, i know its bad ill try be better so yous can understand what im saying, sorry bout the aussie slang if that bothers you but cant help that.

thanks even more for your tips, i returned today and thoughrly cleand condensor, and oh my, it was way dirtier than i thought, i than test run the unit and bingo, head pressure was down to1500kpa(215-220psi), suction pressure was also lower sitting at 140kpa (20psi) too low i suspect, the sight glass was still bubblin and evap appeared to starve (cabinet was warm and unloaded), i squirted some more r22 and found still no change in suct pressure. the owner was keen to leave so i didnt get too play too much, i am getting him to turn on in mornin and i will call later and i will take suggested measurements, thanks again for taking time to reply nike take it easy....

[TECH TIM]

also want to mention the suction pressure was 140kpa, suction line temp approx 10 cm from compressor was 18-20 deg cel..

[nike123]

Hi Nike, thanks for the comment on my gramma, i know its bad ill try be better so yous can understand what im saying, sorry bout the aussie slang if that bothers you but cant help that.

thanks again for taking time to reply nike take it easy....

I will.;)
It is not slang what bothers me, it is lack of punctuation marks. Your text and sentence doesn't have start, middle and end marks, and is one big sausage hard to read (at least for me). That is text formating I speak about in my previous answer.

Look at readability of my answer, if I do as you do:



first thing to do is to clean that condenser coil and be sure that fan is working properly than measure temperature of pipe exiting condenser and subtract that from value of saturation condensation temperature from high pressure gauge or convert it from high side pressure that will give you subcooling value which tell us state of refrigerant charge in system with TXV valves if it is higher tan 8K remove some refrigerant until subcooling is lower than 8K and still above 3-4K allow some time of 15-20 min between readings and than make again readings of system pressures and temperatures suction pressure condensation pressure display cabinet temperature air temperature in and out at condenser temperature of pipe at exit of evaporator temperature of pipe at suction on compressor 15-20 cm from compressor temperature of pipe at exit of compressor temperature of pipe at exit of condenser temperature of pipe at entrance of dryer temperature of pipe before TXV
make temperature readings with accurate thermometer suitable for pipe temperature measurements and please format text to be readable you have 28 year and degree I assume that you should know how to properly format your sentences

Now, tell me, is this something you wish to read, and something you understand easy as original text?

[TECH TIM]

it is hard to read i agree


i know its bad ill try be better so yous can understand what im saying, as i said

[TECH TIM]

hi guys, how are we? just want to keep tou all up to date with this one, what i have worked out is the system was actually charged with r404a, and was tagged r22:confused:, i must not have been thinkin that day, therefore i have topped up r22 on r404a obviously not good, i have returned and recovered refrigerant and hp with nitro, i then released and removed dryer and purged nitro, i replaced with new dryer and tripple evaced system, i have recharged with r404a and have found every thing so far is ok, looks like all i had to do was clean cond in first place and all proberly would have been sweet, anyways im sure ill be more visualant in future with tagging, ill keep you informed as to wats happens with unit, ill be able to inform accurate pressures too once cabinet down to temp, thanks again for your replies nike & piersons_man talk soon ;)

[nike123]

hi guys, how are we? just want to keep tou all up to date with this one, what i have worked out is the system was actually charged with r404a, and was tagged r22:confused:, i must not have been thinkin that day, therefore i have topped up r22 on r404a obviously not good, i have returned and recovered refrigerant and hp with nitro, i then released and removed dryer and purged nitro, i replaced with new dryer and tripple evaced system, i have recharged with r404a and have found every thing so far is ok, looks like all i had to do was clean cond in first place and all proberly would have been sweet, anyways im sure ill be more visualant in future with tagging, ill keep you informed as to wats happens with unit, ill be able to inform accurate pressures too once cabinet down to temp, thanks again for your replies nike & piersons_man talk soon ;)

Good for you!
Now you learned two things:


Clean evaporator and condenser an check proper air flow (or water) before you attach gauges (in fact, do not ever take your tools before that except for cleaning purposes). That goes for every service job in this trade.
Never add charge before you evaluate performance by organized method like this one (http://www.refrigeration-engineer.com/forums/attachment.php?attachmentid=2673&d=1233838982)

[TECH TIM]

Never add charge before you evaluate performance by organized method like this one (http://www.refrigeration-engineer.com/forums/attachment.php?attachmentid=2673&d=1233838982)


thank you muchly nike this is very helpful, i know it is what you have posted basically but i will use this thanks again