How to determine a refrigerant's type? 1

[PQ2]

I have acquired a 25-year old “cryogenic cooler”. The manufacturer sells the stainless-steel insulated box in various sizes and cooling configurations to suit a customers needs. They don't all cool to low temperatures but may cool to temperatures well below -100C if you have enough LN to throw at it. The cooler that I have is mechanically cooled with a Hupp compressor (now out of business I think). This would indicate that it was likely not intended to cool below -20F since it is a small, apparently fractional horsepower, hermetically cooled, compressor. I can not see it since it is hermetically sealed and there is no nameplate data. It struggles to get to +20F after running for an hour or more. Once the set point is reached, a resistance coil intermittently comes on to keep the temperature from going any lower. I have been told that this energy inefficient process is often used to maintain precise temperature control. The condenser is a two row, four pass per row, single circuit coil. There is no TX valve just a capillary tube.

I would like to replace the coolant and fully charge it to see the temperature to which it cools. I do not know what coolant it uses and the manufacturer indicates that they do not have a record of it or the equipment. I have attempted to get various service companies to service it, but no one will accept the assignment until they know what refrigerant it uses.

I don't have pressure gages so I do not know its pressure at ambient temperature. Furthermore, one service company indicated that knowing the P-T relationship isn't sufficient to uniquely identify the refrigerant anyway. A sample of the refrigerant could be sent out for chemical analysis, but I don't know who to send it to or how to package the sample, or it if is cost effective to do so.

Is there a simpler way to determine what refrigerant it is? Once I know what it is, I'll likely have to replace it with something more environmentally friendly. Determining what that is will be the second step in this process.

I can buy a set of gages and a compressor and even take the EPA course so that I can buy refrigerant, but most are only sold in very large quantities like 100 lb cylinders. Issue three is where can I buy a five pound container of a refrigerant?

My objective is to get this piece of equipment up to date with an environmentally friendly refrigerant so that I can determine if it can be used without modification for my purposes. Is there an easier way to accomplish this?

 

[DrRTU]

Most ultra low temp boxes use a cascade system with 2 or more refrigerants. It sounds like you have a medium temperate box that was built to hold 20 deg. Your best bet would be to find an ultra low temp service company in your area. Find out who services blood banks, pharm labs or research labs and pay them to look it.

 

[MikeHalloran]

If it is a hermetically sealed system, and it's still working _at_all_, chances are it's got about the right charge of whatever refrigerant it was designed for.

You don't _know_ that the refrigerant in the unit is problematic, because you don't know what it is.

It certainly isn't a problem _now_, and can't become one unless it's released. Which would probably happen if you tried to replace the refrigerant, because it's not that easy to get a tap valve to seal right on a small system. You'd probably lose all of it before you got the tap valve sealed. Trust me on this.


The unit appears to be doing exactly what it was intended to do. Someone probably paid a lot of money for its special capabilities. Maybe you can find someone else who needs that exact machine, and give it to them, and separately buy the exact machine that you need.

THAT would be environmentally responsible.



Mike Halloran
Pembroke Pines, FL, USA