Ultra low Temp Refrigeration

[elmusasc]

Hi there
I am working on a Harris ultra low which has the 1st stage using 502 and 2nd stage using 503. I was wondering if anyone can tell me what pressures I would be looking at at start up on both stages and what pressures I would see when the box is down to temp.
Also what would be good replacement refrigerants for ultra low refrigeration
500
502
503

Thanks for your help
Eric

[Brian_UK]

If you have a P/T chart for these refrigerants you should be able to find the relevant pressures when at ambient.

The working pressures will be lower of course but you will get an indication.

[chemi-cool]

Hi Eric,

you can simply check the pressure and learn about the temp.
its a cascade system.

You can not use the new refrigerants unless you flush the systems and replace compressors.

Chemi

[jcook1982]

Harris doesn't have Thermo couples on their freezers so you can read temps on evaps and heat exchanger. Tapping into a system is not very well taken. Charges are very critical in UL applications

[ozzy bill]

507, 404a high stage ,132a ,170 ,or 508 with propane

[jomama]

Before you do any service work on a ultra low cascade sys do a little research on low stage refrigerants 508b,503,114,13, ect all use r290 for oil return these are high psi refrigerants and can be dangerous if handle wrong. charging theses sys is completly differant than charging a standard sys. please ask questions for your safety and the safety of others.