So I'm sitting in front of this thing and we have had nuisance LP lockouts. They started last fall and have occurred in both heating and cooling. Current superheat is 8.8 and sub-cool is 31.1. EWT is about 65F and EAT is about 73F. Suction pressure 126 and liquid is 262 both around chart specs. Chart indicates superheat mid teens while sub cool should be as well. This thing worked fine with the charge in it for years (I'm the only servicer as it is my excavator's home) so the conclusion of overcharge is unlikely (in spite of a high sub-cool and low superheat). Really not much to conclude except bad metering (TXV). Any other thoughts?
Joe: I am sure you checked the amp draw on the pump(s) to see how much work they are doing. I also know you checked the service ports for leaks before you put your manifold guage on the system.
Hey Mark, I certainly covered a lot of ground, but the symptom's indication of "overcharge" did not inspire me to look for a refrigerant leak. I'm reasonably sure no refrigerant leaked in. - I've ordered a TXV. Before I cut it in, I'll look for a temp delta across filter drier, but can't think of much else. As you know Mark one of the fun parts about TXV's is they often are changed as much out of intuition as foundation. We'll know soon if my intuition was good. Saw Brad yesterday. We have lost a second (of 5) compressor. Another unit was frozen and left to thaw. I found that air handler pumps 3 and 5 were switched and more stuff leaks. I told Brad we are gonna be pal-ing around for years before this things straight. We delivered his hydronic console as well. Waiting for a shelf for that monstrosity.
I don't do the geo volume all y'all do, but FWIW I'll chime in on TXVs...We are seeing quite a few Lennox ASHP AHU TXV failures from systems 7-10 years old. Symptom is high superheat (30*F +) that does not respond to addition of charge. In an extreme case compressor trips out on internal overload (overtemp) owing to starved suction denying compressor enough refrigerant to keep itself cool. In your case middling superheat and high subcool (assuming proper charge) gives rise to thinking about a check valve that isolates the waterside metering device while in cooling mode...am I making any sense here? Something is backing up refrigerant on the high side. From my southern perspective an air conditioner operating off 65 degree entering water on the high side should be fat, dumb and happy. 262 high side Tsat = 87*F..quite high for a system working off 65*F water...could the waterside coax be scaled / fouled? What's LWT?
