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sork
16-05-2016, 08:07 PM
Hi lads
working on coldroom, condensing fan was burnt out , replace the fan, then i realised the evap covered in ice, did a manual defrost, start the system, temp pull down until -1.5 c , in half an hour the whole of suction line was frosted, evap fin was covered in frost, suction temp 20psig, from then unwords compressor could not pull down anymore. the sight glass is full , i have check the charge myself in 2014 , i wonder why? is it faulty compressor or moisture in the system? or expansion vale is not metering properly!!! when i turn the unit on in 30 min the evap fin and the suction line covers in frost,i neet to obtain at list -10 -12 any advise or help is appriciated. running on R404a

niceman
16-05-2016, 08:27 PM
Are evap fans running? Are both running correct rotation? Have had fan capacitor fail on one fan and draught from other fan gets it going in wrong direction, so no air flow thru evap, only around fans, worth a look.

vikky1971
16-05-2016, 08:35 PM
Hi sork.....system running with insufficient cooling leads to high pressures and high temperatures, resulting in carbonisation of lubricating oil. This carbonisation will clog the expansion valve, that may explain the frosting and inability of the system to attain the required temperatures.

Craig Johnston
16-05-2016, 08:42 PM
how do i start a new post. thanks

sork
16-05-2016, 09:03 PM
nice one Vikky1971, what is the solution?

sork
16-05-2016, 09:05 PM
thank you Niceman, yes there are 3 fan in the cooler, they are running all right, they 10 w , i do not know about running in reverse, but must check weather they are pulling ok.

sork
16-05-2016, 09:06 PM
go to the top and explain your problem in simple form.

sork
16-05-2016, 09:19 PM
Mr Johnson. if you click on forum, then at the top left hand side written POST A NEW THREAD , click there, a page will come up , as you replied to my post. good luck, now let me concentrate on my problem.

Craig Johnston
16-05-2016, 09:22 PM
post a new thread is not on my webpage. thanks anyway.

sork
16-05-2016, 09:35 PM
Mr Johnson. this is what i do. i went to forum , from the list on refrigeration division, i clicked on commercial, a page apears, on the top left hand side , is written commercil above it is written+post new thread, click on that , then Bob will be your uncle. chears

vikky1971
17-05-2016, 07:55 AM
Hi sork, you need to flush out the lubricating oil which has carbonised with nitrogen preferably. Clear the full system of any solid particles. Install a independent dryer cum filter cartridge before the compressor. Make sure that the expansion valve orifice is clear. Take recommended lube oil for the compressor and as a regular practice, before charging gas put entire system under vacuum and then charge gas. I hope this should be of some assistance to you.

sork
17-05-2016, 03:30 PM
thanks Vikky very kind of you, the minute i saw the cooler clogging , i guessed i had problem. when you left the reply , i knew you are right; nothing else has the same symptoms. the metering device was covered in ice bulb as well. i did not bother to heat it a bit , as you say the system is very dirty; anyway it is just a hermatique comp. i noticed today as the system running riches -1 to -2 when stops maybe overload or relay, the condenser fan still running, comp has an internal overload, has not called for a defrost yet.

sork
17-05-2016, 03:34 PM
maybe the voltage leakage is due to the same problem.

monkey spanners
17-05-2016, 04:36 PM
Had a system with very similar symptoms recently, after replacing the compressor that had broken valves it turned out the condenser fan was faulty and had led to high head pressures, found the expansion valve strained blocked with dirt, so fitted a new orifice and has been running fine since.

Sounds like your compressor is going off on the klixon possibly due to high suction superheat due to the restricted expansion valve.

Heres a video of what i found, skip to near the end to see the dirty orifice filter,

https://www.youtube.com/watch?v=Y7nF2AWenmU

sork
17-05-2016, 05:21 PM
monkey spanners. did you say ? you just changed the compressor and then expansion valve was clogged? was your coolers fin blocked the air movement? i change this compressor two years ago, working fine always -17 c no prob. i want to first put a permanent magnet on the mag valve( request of a good eng). then i want to check the expansion valve orifice.

sork
17-05-2016, 05:29 PM
when the box reaches -1 c by then, the cooler fin are completely frosted and the frost acts as a shield thus ,not allowing the air movement by the fans to cool the room, so comp runs pushing the oil and the ref to the evap and icing up.

monkey spanners
17-05-2016, 06:01 PM
monkey spanners. did you say ? you just changed the compressor and then expansion valve was clogged?

Yes the original compressor still ran but did not pump, once a new compressor was fitted and after half an hour or so of run time the expansion valve blocked up. Once this was sorted out and the system restarted the condenser fan failed to start due to a faulty capacitor, i think the faulty fan motor is what lead to the original compressor failure.

cadwaladr
17-05-2016, 09:46 PM
It's good practise to change the txv when changing the compressor,most small compressors replacement cost is close to changing the condensing unit

PaulZ
18-05-2016, 01:27 AM
Hi sork
You said the sight glass is full, is it before or after the liquid line drier? A full sight glass is not always an accurate sign of full charge as you said you checked the charge in 2014.
Have you checked the TXV superheat and if so what is it?
Have you shut the liquid off and bridged the LP to see how far into a vacuum the suction will go? If the compressor struggles to pull down then as MS suggests the compressor is probably faulty.
A bit more information would help.
Paul

sork
18-05-2016, 05:14 AM
Hi Paul.the evap fans at -1 c are blocked by frost,how can she pull down?there is no movement for air circulation,i agree with you the comp might be faulty,but at 30 ambient discharge is 320 psig and suction 30 psig. This is one very strange situation, comp pulls down from 10 to -1 in 20 min , i have not seen a faulty comp that sufficient yet,in pump down i noticed when comp off cycle ,suction was in vac.there might be a slight high dischage,that is not significant. I think suction is high when covered in frost. But there is no floading of ref to comp,comp is not hot,

sork
18-05-2016, 05:31 AM
I lowered the LP to 10 psig, while i was there comp did not shut down. I bypassed LP , i am going to disconnect mag vavle coil by using permanent magnet,i will be checking the bulb position then i will have access to check supperheat and subcooling. I will check the orifice after. Maybe the coil fans need to be watched again while she is pulling down,maybe they stop and run periodically. this seems to be a possibility.

sork
18-05-2016, 05:39 AM
On electrical front, when comp stops the condensing fan does not stop, but the evap fans stop, i need to make them run while comp off from the controller.

Recoilzn
18-05-2016, 05:52 AM
10w fan motors might be too small for a coldroom, thus resulting in slower air movement over coils. I have never seen a freezer with 10w fan motors. Try a 25w fan motor.

niceman
18-05-2016, 06:10 PM
Did the freezer get to temp on existing fans before breakdown? If yes then fans ok. Are you 100percent sure no ice left in evap stopping air flow?Can you shine a light through. When condenser fan failed hp probably horrendous, R404a breaks down under hi temps. If all else ok you should evacuate system and fill with new R404a. Have had this happen on freezer cabinets. Best of luck. Also sounds like you need more ventilation where condenser is.

sork
18-05-2016, 08:33 PM
Thank you everyone, i cheched the txv today no frost it means refrigertion is fine, due to lack of defrost the bulb was covered in ice again. I defrost the system manually, then the usual check outs subcooling at 4c suction superheat 15c system pull down ok. I need to change the controller which its relay burnt out on def terminal, been trying to solve that problem.

Glenn Moore
20-05-2016, 09:10 PM
sork
15C superheat is excessive for a freezer, it should be about 4-6k superheat otherwise you are starving the evaporator of refrigerant and causing the system to run with a depressed suction condition leading to poor efficiency
try opening the TEV a couple of turns ,if that doesn't work you may need the next size bigger orifice.

sork
24-05-2016, 04:56 AM
Thanks everone,suction supperheat down to 8 and roo temp was _15 c when i ask them, so it ok. The prob was the low lp malfunctiooning and tvx needed adjustment to reduce supperheat.

sork
24-05-2016, 05:06 AM
Big THANKS everyone.