# Thread: Environmental Test Chamber -- Cascade -- Low stage not working

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Originally Posted by Poodle Head Mikey
So the manufacturer's position is that a chamber listed to get down to more than -70º F. in an hour - which will barely get below -50ºF. in three hours is performing in a standard "typical" manner? If so; it would be difficult for me to imagine an engineering department with a wider standard deviation. <g>

Always do the easy things first - static pressure is 65 when it is supposed to be 75. So I would start there. Let's see if any of the whiz kids here know if 508B fractionates too much to top off. Either way; in my crystal ball I am starting to see a high pressure refrigerant purchase in your future. <g>

How big is this thing physically? The smallest ones I typically worked on were about the size of a small van. Although some were the size of buildings. <g>
Well to be precise, it's rated to go to -40 in 15 minutes, and mine takes over 1 hour. But yes, the refurbisher is saying that this performance is perfect.

The whole machine is about 3 feet tall, 3 feet deep, and 5 feet wide, and weighs 500 pounds. There is no "skid," no place to put forks or a lifting hook. We use four guys to lift it and move it. I understand this would classify as "tiny" in your book but to us it's pretty big!

To illustrate the performance, I attached a plot of two cooling curves. One curve was when the chamber's work space was empty, and the controller was programmed to the lowest set point (S.P.) possible. Notice how the chamber began warming back up. I turned it off at that point because I knew from experience that it would never get any colder.

I also plotted the "benchmark" curve using data from the table in the datasheet. The table gives time, in minutes, for the chamber to change from ambient to the given temperature. It lists times for all but the lowest temperature, which makes sense because it's an asymptote. I just called it 300 minutes for the sake of plotting on the same graph as the other curves.

2. Oh sorry - I was thinking F. -73º C is more like -100º F. At first I was thinking: what a relaxed job that 508B has to do. <g>

So where are we going from here? If you don't have the tools to work on this thing - what's The Plan? <g>

3. ## Speaking of which -

What part of the world is this machine in?

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It is located in South San Francisco. I am looking into what it would cost to get it repaired locally, but we may also send it back to the refurbisher. It's unfortunate to have to pick this thing up and move it again but I want to get it working correctly.

5. A guy flew me out there to rebuild an antique diesel boat engine one time. Volvo was useless for parts but I rode down to Oakland and first found a biker bar and then a biker machine shop. We made the new valves for it. I forget now what the beer tab was but all the parts and machine shop work cost me about a hundred dollars. <g>

I've sometimes wonder what the next guy to work on that engine thought: custom valve guides, custom valves, hand made copper gaskets, etc. <g>

PHM
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Originally Posted by quicksparks
It is located in South San Francisco. I am looking into what it would cost to get it repaired locally, but we may also send it back to the refurbisher. It's unfortunate to have to pick this thing up and move it again but I want to get it working correctly.

6. ## Seems like there must be somebody on here near SF

It's not rocket science to fix and why pay to ship the whole unit out and back? Maybe start a new thread on this forum for a low temp refrigeration guy near SF ?

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Originally Posted by Poodle Head Mikey
It's not rocket science to fix and why pay to ship the whole unit out and back? Maybe start a new thread on this forum for a low temp refrigeration guy near SF ?
There's an idea. I will run this info. by my boss and see what he wants to do.

I hope the boat's owner appreciated what you did for his motor!

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Hmm. My company has a shop in Union City...

Fractionation - I could be wrong, but I've been under the impression all this time that only the zeotropic blends were prone to fractionation. (All the refrigerants with a number starting with 4- 404, 414, 403, 409...) And that the azeotropes (start with 5- 508, 503, 502...) didn't fractionate. What say you smarter people?

The static pressure being a bit low in that low stage isn't really uncommon. It soaks down into the oil some... That said, you really don't have to lose too much of it to start seeing serious changes to your cooling rates. Test chambers tend to be really hard on compressors as well, it's not uncommon for compressors to be a bit inefficient after just a few years.

9. Originally Posted by cmclifton
Hmm. My company has a shop in Union City...

Fractionation - I could be wrong, but I've been under the impression all this time that only the zeotropic blends were prone to fractionation. (All the refrigerants with a number starting with 4- 404, 414, 403, 409...) And that the azeotropes (start with 5- 508, 503, 502...) didn't fractionate. What say you smarter people?

The static pressure being a bit low in that low stage isn't really uncommon. It soaks down into the oil some... That said, you really don't have to lose too much of it to start seeing serious changes to your cooling rates. Test chambers tend to be really hard on compressors as well, it's not uncommon for compressors to be a bit inefficient after just a few years.
508 can be topped off, worked on a few cascade systems for Johnson Controls and never had any issues with top offs...

Hope this Helps

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Originally Posted by skpkey9
508 can be topped off, worked on a few cascade systems for Johnson Controls and never had any issues with top offs...

Hope this Helps
Thanks for your response. Good to know it can be topped off.

cmclifton, what is your company? Do they make house calls?

11. Originally Posted by quicksparks
Thanks for your response. Good to know it can be topped off.

cmclifton, what is your company? Do they make house calls?
Florida Air Care

Wish I could but way to busy....

Also 404a can be topped off as well

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Does anybody know or have literature on how to flush a cascade freezer with RX-11? It would be greatly appreciated.

13. Originally Posted by joebuck585
Does anybody know or have literature on how to flush a cascade freezer with RX-11? It would be greatly appreciated.
Why do you want to flush it?

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