Tonight was
Practical application of TE collection in attempt to FIX something time. As in the air/air heat pump that was put in before the geothermal and was left in place because it can do cooling too, at least before it broke. With temperatures around 26 old science degrees in the shade, cooling became a priority. Or so thought my wife. I'd already concluded "It's got a three-phase inverter motor driver and blows its main fuse, schematic is unobtainium, I'm calling thyristor fault. Some other day." which of course was not enough. And rightly so!
Since the fuse blew only on compressor start ( that was my theory; there was a small delay before POOF) the problem would be in the external unit: that I was pretty certain of. We crawled under the house, where the external lives, with dust and mosquitos. After some cleaning out and checking of caps with the DE-5000, I looked over a few power resistors on the PCB with my Fluke 10. All, caps and resistors, were comfortably inside their tolerances, nothing looked strange. My prior attempts had been done solo, but with the wife at hand to push the power on while I was looking at the open unit from a suitable distance (comms set up via my Baofengs using one of the no-license channels), we fitted another fuse and turned things on, which led directly to a
BANG and sparks coming out of the bottom of the unit. The defroster circuit has a
bi-metal thermostat which opens on rising temperature, and it was from that area that the sparks and noise came. It so turns out, that the position in the bottom of the unit where the thermostat sits is prone to contamination, and there simply was arcing to ground from the defroster circuit, through a path of gunk, at the thermostat.
I drilled out the pop rivets holding the thermostat, disconnected it, took it inside where we cleaned it thoroughly, megged it (Crank "Wee" Megger, of course) which it withstood well. Then I hooked it up with the 8060A in continuity mode, pressed an ice cube at its sensing belly and was rewarded with a "Click! BEEEEEEEP" which promptly stopped once I'd patted it dry and heated it in my palm.
Another round of cleaning, grabbed a rag and some brake cleaner in the garage, along with new pop rivets, cleaned the area around the thermostat and then reassembled things. Fitted a new fuse in the panel, turned things on and everything took off where it had been where the unit last had worked. That was in the winter though, so it immediately tried to heat the house...
![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
One house project done. So many more to go.