Hi all, new here and was hoping to maybe get some pointers on a project I'm working on .. not sure if this is the right subcategory though? Basically I found a brand new mini split condensing unit for $30. It's fairly small at only 800W input power, but should be more than sufficient for my needs. My intentions are to use this to cool water (or some other fluid). I purchased a brazed plate heat exchanger and fitted it directly on the unit. Obviously this setup is completely different from what the unit is intended to do, so I realize there's a bit of "hackyness" going on here. This is just for my own personal use, so I'm not overly worried about whether the unit might only last a couple years running like this etc.

Basically I'm a bit lost on how I should be checking refrigerant levels on it. Being a mini split, it has an internal expansion device (just capillary in this case), so the discharge side literally just goes through the 1/4" tube right into the heat exchanger. That said, it only has a service valve on the suction side, so it's basically my only indication of what's actually going on inside the system. I noticed however that both the suction and discharge lines freeze up quite rapidly, so I'm thinking it may be low on refrigerant. I stuck my gauges on the suction service valve and measured probably around 25psi - with ~20C water running through the heat exchanger. Turned off, the system sits at about 110psi. This seems quite low, but I realize the pressures and temperatures are all dependant on the load.

I'm just trying to get my head around the proper way of measuring such a unit .. should I just connect it to the garden hose and let "ambient" temperature (28C) water flow through it and see what the pressures are at then? Or should I be regulating the water flow so that it comes out at say, 1C?

The main problem here is not having access to the high side pressures, but apparently this is common on mini splits, how do you know if they're over/undercharged?

Cheers,
Dan