Small Chiller unit problems

[theapprentice]

At work Im currently working on a bay maree that has be converted into a little display cabinet to house fruits salads and the like. The problem was a locked rotor compressor. So I have changed the compressor but today when I went to recharge Im not sure how much gas to put in as there is no charge information and its kind of custom made so cant ring any suppliers. It has a small coil underneath the floor of the bay maree. Its only running about 40-60 kpa suction on R22 with about 1.3kg of gas in it and a superheat of about 30 degrees kelvins. Im thinking its still a little undercharged. the coil is only static there is nothing to transfer the air around inside. The sight Glass is clear all the time, the head of the tx valve is freezing up and where the coil runs underneath the floor of the unit is developing a ice pattern but not the whole way around on the frst half or so. Im after some ideas on how to check the charge whether to keep adding or what. Hope all this makes sense,
Chris.

[The Viking]

First, to determine if you got the correct charge you will have to look at sub-cooling and sight glass.
The sight glass is clear, so during current operational conditions you got enough refrigerant in there.

BUT, your super heat is way off the mark.
Somehow, you will have to reduce it, possibly by adjusting the TXV.
Start with checking that you haven't got any blockages anywhere (most likely, there will be a fine mesh strainer in the "inlet" to the TXV)

Good luck

[theapprentice]

yeah the valve is on its lowest superheating setting. Alright I will check out some other things before checking the strainer. The thing is the other unit they have converted into a small chiller is always coverd in ice on the bottom where the coils run, there are just not made for the job they have be convertd to do. What sub-cooling should I be looking for. If there is to much sub-cooling is that undercharged??? For example range is 7-11 from memory if its 25 does that mean undercharged

[The Viking]

If the sub-cooling is HIGH, then the system is OVER charged (assuming that there aren't any other problems with the unit).

Search this board for sub-cooling and you will see that it's a subject with a lot of different views on what it should be. The bids ranges from 0K to 15K, it all depends on whom you are listening to.
My personal preference is 6-8K.

[paul_h]

an r22 system should at least have 200kp suction, if the sightglass is clear, I'd say it's empty of liquid.
Shut the reciever service valve for 20 sec and open and see it if anything happens in the sight glass.
1.2kg is a big charge, so it's strange situation. Try removing the TX valve bulb to see if the suction pressure changes, or wind the tx adjustment fully in, then count out 3 full turns. Since you're doing a compressor change we can't rule out things that could have caused the original burnout, so check the TX valve with these methods, also blow through the condenser with compressed air/nitrogen. Or clean it with detergent/solvents if it's greasy.
I hope you've already changed the filter/drier?

[Gary]

The first thing to keep in mind is that the TXV superheat is supposed to be high when the refrigerated space is warm. You cannot accurately adjust a TXV until the space is down to its temperature range.

Unstrap the bulb and hold it in your hand. Warming the bulb should cause the TXV to open wide and flood the coil. If it does not, then adjusting the TXV isn't going to do anything and the problem lies elsewhere.

If this is the case, given that the sight glass is clear, the most likely problem is a plugged inlet screen in the TXV.

[declan simmonds]

Hello i would also check your condenser coil make sure its super clean maybe its blocked with crap
good luck but i think its something to do with the txv also and i would also check to see if the condenser can pick up clean air and make sure its not recirculating back to the system
good luck

[SteinarN]

Whats comes into mind with only part of evaporator cold, to high superheat, full sight glas, frosting ocuring at/after the TXV and max open TXV is the size of the TXV or the orifice. What model TXV is it? Has it changable orifice and what size orifice?

[The MG Pony]

My answer? Audit the system, check and messure every inch, then go from there and systematicaly verify each and every component.

[iceguy]

the easiest way to charge the unit in these sort of situations is to stop the evaporator fans and charge the unit until the coil becomes fully frosted to the accumulator if fitted. you wont be far out doing this. good luck

[Brian_UK]

the easiest way to charge the unit in these sort of situations is to stop the evaporator fans and charge the unit until the coil becomes fully frosted to the accumulator if fitted. you wont be far out doing this. good luck

If you read the first post correctly you would see that there aren't any fans to stop.

the coil is only static there is nothing to transfer the air around inside

[theapprentice]

Found out some interesting informartion today. The unit is made by roband its one of there refrigerated baine marees. Its meant to have 1.5kg of 404a in it. The guy who worked on it before me did something and god only knows why made it a 22 system. I put the 1.5kg of 22 in it to see how it would go the best I could achieve was about 10-12 degrees C. Is there any chance I can make it work with out having to change it all over. And could someone please describe the diferences between the 2 gases. Cheers everyone
Chris

[nike123]

Found out some interesting informartion today. The unit is made by roband its one of there refrigerated baine marees. Its meant to have 1.5kg of 404a in it. The guy who worked on it before me did something and god only knows why made it a 22 system. I put the 1.5kg of 22 in it to see how it would go the best I could achieve was about 10-12 degrees C. Is there any chance I can make it work with out having to change it all over. And could someone please describe the diferences between the 2 gases. Cheers everyone
Chris

What oil is in your new compressor and what oil was in old one? What is TEV valve make and model and orifice no.? What is compressor make and model no.?

[The MG Pony]

Again we need a full audit of the system to help at all other wise it is all gues work at best!

[Kh1971]

hi,

there is somthing blocking the pipe line please check

[theapprentice]

what makes you say something is blocking the pipeline. Its a fr6b danfoss compressor. tx valve is a danfoss one dont know model off top of my head, but it is a r22 valve. thats all i know till I got back to work in the morning.
Chris

[philfridge]

Hello sounds like a lash up . A DANFOSS FR6B is a R12 COMPRESSOR with mineral oil. So you should not be using r404a or r22 . Best to use R409a which is a drop in gas for r12 . Also you will have to renew the tev as it sounds partially blocked and it is a r22 valve. You will need the correct tev (r409A) for the gas being used . ok

[The MG Pony]

Oh goat! you got your work cut out for ya. Basicly at this rate your ending up to having to rebuilt it from scratch!

[Gary]

This may not be the ideal compressor for the application nor the ideal refrigerant. So what? The compressor doesn't care what kind of vapor it is pumping and R22 (assuming the TXV is R22) can do the job.

Clean the inlet screen and pat yourself on the back for a job well done.

[philfridge]

Forgot to tell you R404a requires polyester oil in your compressor and r22 requires mineral oil . If like you said the gases have been changed that is possibly why you have a blockage as they are not compatible with the incorrect oil . That is why compressors have labels ??