Pressures in chiller

[bartx]

I'm building my first chiller. I've built a few single stages, so I have some experience, but chiller is a bit different. I'm using Teco 5.3k btu rotary, 1.3kw luve condenser, 10 plate heat exchanger. As expansion valve, I'm using two 0.8mm captubes, each is 150cm long, refrigerant is pure R507.

My question is what pressures I should expect, when unit will be loaded using 550W tea heater (I can't find photos with manifolds anywhere on this forum). So far, I have about -25C liquid temp idle, but on 550W it's +2C, and pressures are 17 barg discharge, 2.2barg suction. Unit seems to be undercharged (suction accumulator isn't cold), but It may be caused by bad vacuum, I'm almost sure, that there is some air in unit which makes my pressures so high. But before I charge it once again, I'd like to know roughly what can I expect. Maybe captube is a bit too long, I have no idea. Help will be appreciated

[Stewie007]

So many questions...

When you evacuated the unit, did you do a triple evac and perform a standing vac test?

I find that people like to run as low as they can go. Your evaporator probably isn't getting enough refrigerant to absorb the amount of heat your system is putting off. Under idle its no problem, but add a load and bam!

Also, what is the ambient temperature of the room? What is your condensing temperature? Capacity has a lot to do with this temperature. The system rating is for specific and known parameters. For example, my Tecumseh compressor is rated at 1865 BTUs with an evap temp of -10F. The condensing temp was 49C. However, my water cooled condenser will probably enable me to do about 40C or if I'm lucky even 30C condensing temp. With greater subcooling at a lower condensing temperature, the unit will have more capacity at the same evap temp.
Ive also got a handy temp/pressure chart for you.

Edit; I forgot to ask. Does your temperature remain stable at 2C? Your tea heater gives constant load while a CPU typically does not.

http://www.watco.com.mx/HTCPressureTemperatureChart.pdf