We have a through-the-wall type AC in one room. It works well most of the time but when it's the slightest bit cool outside, the compressor won't kick in no matter how warm it is in the room. Yes we can open the windows but let's say we don't want to.

I pulled the front cover and noticed a capillary tube along the evaporator face. I routed the capillary tube away from the evaporator face and warmed it. The compressor didn't kick in. Maybe it's an evaporator temp sensor to prevent icing and not the ambient temp sensor.

Question - what is the typical thermostat and temp sensor arrangement on an AC like this? I can see that I have to pull it out of the wall a little bit to get to the control innards so I'd like to be armed with a little knowledge so I don't have to do it again. On the plus side it looks to have very basic analog rotary controls, not the new fangled soft touch controls with LED display (which probably work better ).

Thanks,
Sixto
95 S420
87 300SDL
99 Panasonic CW-C101MU

That cap tube is part of the thermostat and you should put it back where it was. You're most likely dealing with a failed/failing thermostat that is intermittently sticking with the compressor contacts open.

The cap tube contains a fluid which expands and contracts depending on the temp of the air. This fluid forces contacts in the thermostat body to open or close which then allows current to flow to the compressor. Sometimes, the mechanisim that moves the contacts together will get corroded or simply wear out and quit working reliably.

Next time it stops cycling the compressor, and you know that compressor should be on (ie warm enough have the contacts closed) try gently tapping the temp selector knob or, better yet, the shaft of the temp selector, with a screwdriver handle. Bumping the knob/shaft will usually get the contacts to go ahead and snap closed.

Oh, one more thing...if it has a filter (foam thingy) over the evaporator, make sure it is clean.

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