OK, guys. Here's what I don't understand: it sounds like the system was building up head pressure and eventually the internal relief valve was venting back to suction side. This would continue until the internal overload in the compressor would finally kick out. After cooling off awhile, it would reset. My question is this: how would a bad TXV cause this to happen? Why wouldn't it just pump down, and cut out on low suction pressure? Or just continue to run into a vacuum? Why the excess head pressure?
many resi units do not have low presssure switches.
So where is all the heat coming from to elevate the Head pressure? If the low side is into vacuum it's not moving any heat from the evap. coil. All the refrigerant is stacked in the condenser and liquid line, being cooled down to ambient. Is it possible that the high compression ratios and the heat of compression are responsible for all the excessive head pressure? I've never witnessed a system running long term into a vacuum with no LPCO to know the effects this has.
It's an R-22 system, circa 1996. The tech said the same thing: he rarely has problems with the R-22 systems, but often replaces various sealed-system parts on the R-410 units because of the higher pressures.