-80 C Cascade freeser,high stage temperature unstable.

[nizu]

Hi,i´m a service engeneer and my company selling Sanyo,Panasonic biomedical instruments.
freezers,incubator,climatc chambres etc...
We do not do fix refridge units yourself, we ordering this work from local refridgeration repair companies.
But i think they do not have much experiens here with cascade systems ,so I need little bit help.
I think they did something wrong.
Everything started in one day the low stage compressor burned out,there was shorcut in coils.
I ordered from factory a new compressor,original was Sanyo C-D110E51 but it was replaced with Toshiba compressor, i can check the model if it necessary, and local company replaced it.
But i think not correctly:
Freezer control electronics works: first starts running a high stage compressor, cascade condenser has a temperature sensor, when -34 C is reached then Low stage switching on and should run until the chamber temperature is reached, then low stage starts switching on/off for holding the temperature in chamber, high stage running 24/7.
High stage should make -34C in 20min, but it takes 30-40min.
When the low stage switching on, then cascade temperature (-34C) starts increase, and when it increases to -12C, that is an error for electronics and it switching low stage off, so freezer will never get the chamber temperature.
Also what i heard, is like oil babbles moving in sytem and the low stage compressor does not stop normally, it stops immediately, bump...
factory recommend refridgerants: H R407D 483g n-pentane 52cc, L R508 260g n-pentane 58ccI I see from invoice,which they but in: r134a 100g, r-407c 500g, r508 350g
What can be wrong? What is the correct procedure when changing the low stage compressor.
I would very thankful for any help!

Freezer diagram is heare:
MDF52_.JPG

[install monkey]

407c added but recommends 407d??

[The Viking]

First of all,
When working on these systems cleanliness and a very deep vacuum is a must. Back when I worked on these we had specialist connectors to allow for the deepest vacuum possible.
From memory there should be a triple vacc where the last one reaches below 100 micron standing for at least one hour.
Then there is the issue of charge, these beasts are charge critical both when it comes to type/quality and quantity. A couple of grammes either way and you will loose capacity, the wrong refrigerant...

Working on these type of machines do require specialist knowledge as well as specialist tools. Chances that it will be correctly repaired by just calling in the local fridge engineer is probably 50/50 at best unless you ensure he/she have worked on these in the past. (Before I was allowed to carry out warranty repairs on these type of machines the manufacturer insisted on me attending their training for 2 weeks and passed their exam and I had been a "proper" refrigeration engineer for 15 years before then)

[r.bartlett]

First of all,
When working on these systems cleanliness and a very deep vacuum is a must. Back when I worked on these we had specialist connectors to allow for the deepest vacuum possible.
From memory there should be a triple vacc where the last one reaches below 100 micron standing for at least one hour.
Then there is the issue of charge, these beasts are charge critical both when it comes to type/quality and quantity. A couple of grammes either way and you will loose capacity, the wrong refrigerant...

Working on these type of machines do require specialist knowledge as well as specialist tools. Chances that it will be correctly repaired by just calling in the local fridge engineer is probably 50/50 at best unless you ensure he/she have worked on these in the past. (Before I was allowed to carry out warranty repairs on these type of machines the manufacturer insisted on me attending their training for 2 weeks and passed their exam and I had been a "proper" refrigeration engineer for 15 years before then)

Don't want to hijack the thread but your PM box is full..


I have been asked to calibrate some of these small freezers. I have a UKAS certified temp probe and was just going to put my probe next to the sensor and compare.

What do you think??

Any advice most welcome

Richard

[install monkey]

some low temp freezers have k type probe connections- for plugging into , as you would damage the door seal if you used a probe and a hand held thermomenter- best to get a data logger so you can moniter the pull down temp.

Don't want to hijack the thread but your PM box is full..


I have been asked to calibrate some of these small freezers. I have a UKAS certified temp probe and was just going to put my probe next to the sensor and compare.

What do you think??

Any advice most welcome

Richard

[al]

or a wireless sensor?

[R. skiffington]

R407D is a blend of R134a and R410, they have charged 134 and 407c. This is your problem, left running like this will cause high stage compressor failure.

[R. skiffington]

It also looks like the ratio is wrong,

[nizu]

Thanks a lot for everybody, i´m a little bit wisier.At the moment i try to find a new partner but it´s slightly hard here. Also problem is R508 refridgerant,only this company has it, which made that work.
Can the R407D replace with another refridgerants, blends?

[The Viking]

Yes,
In theory you are able to change refrigerant. However, that will be a long process in applications like these. An awful lot of R&D involving lengthy testing and replacement of various parts in order to reach the required capacity and temperature.



.

[R. skiffington]

Why would you want to change refrigerants. R134a and R410a are very common here in NZ, is that not the case in Estonia? I think you might find you don't have a problem with the low stage so just have the high stage recovered, evacuated and recharged corectly and, fingers crossed, it will be ok.

[The Viking]

Agreed, R134a and R410a is common as muck unfortunately for the original poster his system should be on R407D and R508 which is slightly less common...

Why would you want to change refrigerants. R134a and R410a are very common here in NZ, is that not the case in Estonia? I think you might find you don't have a problem with the low stage so just have the high stage recovered, evacuated and recharged corectly and, fingers crossed, it will be ok.

[R. skiffington]

Agreed, R134a and R410a is common as muck unfortunately for the original poster his system should be on R407D and R508 which is slightly less common...

R407d is a blend of R134a and R410a, it is easily charged to make R407d, I can't Remember the exact ratio but its something like 33% R134a and 67% R410a.

[R. skiffington]

Sorry got that the wrong way around, the R134a makes up the majority, not the R410.

[R. skiffington]

Just checked its 70% R134a, 30% R410a. Hope this helps.

[The Viking]

Yes in theory you are correct.

To make the required 483g of R407D you could use 338.1g of R134A, 72.45g of R32 and 72.45g R125. (as R410A also is a blend)

However, in these applications where the systems are pushing the possible to the limits even when they just leave the factory even a minor imbalance of the refrigerants will have negative effects on the performance and function of the system. Not to mention the fact that any moisture what so ever will kill it.

Would we really trust the engineers who did the original job, as described in this thread, to both have the knowledge and the equipment to start mixing refrigerant blends in their workshop?
(Nothing against those engineers, I just believe they are outside their comfort zone)



.

[R. skiffington]

Yeah Viking,

Good point. The ULT's I mostly work on are revco, which I find good. The sanyo's seem to be more temperamental, however I find charging the 410a as a liquid (as its 50/50 R32 and R125) works ok. You're definitely right regarding moisture/contaminants with these systems. Those complacencies we can get away with (not saying we're complacent but you'll know what I mean) on everyday refrigeration, you can't get away with on these. Everything must be done by the book, ie vacuum measured and recorded after evacuation, charge must be bang on etc. we once had a new low stage compressor on a Sanyo pull down to set point and run perfectly for 48 hours before ceasing. Sanyo wouldn't come to the party as our documentation wasn't up to scratch, even though everything was carried out by the book. I believe it was a failed oil separator which caused the failure and now recommend it is always replaced with compressor. Lesson learnt.
I do enjoy working on these every now and again but give me something over 30hp anyday!