How I finally solved that phantom AC humming — steps that actually worked

I ran into this exact issue with my Kuhl SS12 last August during that week of 95-degree humidity. I heard that low-frequency buzz coming from the wall even after I hit the remote, and sure enugh, the fan wasn't spinning but the compressor was still vibrating. Pulling the 115v plug was the only way to kill it. When I finally got the front panel off, the evaporator was a solid wall of white frost, just like you described.

In my case, it wasn't just a dirty filter—I'd actually swapped that out a week prior. It turned out the contactor points had pitted so badly they basially welded themselves togather. I think the constant cycling from my Nest thermostat was wearing it down faster than the factory controls woud have.

If anyone else is seeing this, don't just wait for the ice to melt and plug it back in. I tried that and it just froze up again within two hours becasue the compressor never took a break. I had to source a replacement Omron relay and solder it onto the board because I didn't want to shell out $300 for a whole new control module. It’s been three weeks and so far, the humming hasn't come back.

You're lucky you didn't toast the compressor. Those Omron relays are notorious for sticking, but I'd also check the run capacitor while you've got the case open. If it's bulging even a little, it'll make the compressor draw way more juice and fry your new relay pretty quick.

It's a cheap $15 part compared to a new board. Also, don't leave it plugged in at all if it's humming—I've seen 'em get so hot they start smelling like burnt plastic. If you're alredy soldering, might as well do the full tune-up.

One factor often overlooked in these high-amperage Friedrich units is the integrity of your local power supply, specifically whether you're experiencing a significant voltage drop due to an undersized extension cord or an overtaxed 15-amp circuit which inevitably increases the current draw across those contactor points. If your line voltage dips below 108v during peak grid demand, the solenoid might not provide enough electromagnetic force to cleanly snap the contacts open, leading to the exact kind of arcing and subsequent micro-welding that causes that persistent 60Hz hum. I would highly suggest taking a multimeter to the receptacle while the compressor is under load to verify you aren't starving the unit of neccessary potential.

Spot on about the line voltage, but check your fan motor capacitor while you're at it. On the Kuhl SQ or SM series, if that dual-run cap starts drifting, your RPMs drop just enough to kill the static pressure. You think it's a stuck relay because of the frost, but you're actually just not moving enough CFM across that evap coil. I usually swap the stock caps for a USA-made Amrad Turbo200. It’s overkill for a window shaker, but those silver cans handle the heat way better than the cheap Chinese ones Friedrich's been shipping lately.

Quick update — pulling the plug definatly confirmed it was a stuck relay like I thougt, but checking the dual-run capacitor as suggested was the real game-changer. The cap was definitely bulging. I swapped the relay and the capacitor, but I’m still hearing a faint rattle. Do you think a slight voltage drop from the 15-amp circuit coud still be stressing the new components?