AC sheet

[hunterhawk]

Im the original poster and i also have not got my problem resolved.. my thermostat and ac unit are not on the same page. The ac unit just keeps running even though when inside temp reaches set temp and shuts off fan..

[ray1970]

Just a helpful tip for any of you with a digital type thermostat. Don't forget those things have batteries in them. Mine does really wiggy things about every two years or so when that internal battery starts running out.

[fitterjohn]

It sounds like you have a bad thermostat or a shorted stat wire if the condensing unit keeps running after the call for cooling is satisfied. Or your contactor is welded shut. But your out side unit running with out the furnace fan running is one of the major ways to damage a compressor. It won't boil off the liquid refrigerant without the indoor fan going, then it sends liquid back to the compressor and tries to compress a liquid( which can't be compressed) and Bam broken internals, or it will wash the bearings and cussed a short. It's known as slugging the compressor.

[hunterhawk]

Good to know.. i have been turning it on and off

[Danimal]

I just went through all of this. Here is what I found:

Just to make sure we are on the same page, this is how my system works. Outside unit, powered by 240V 40A circuit breaker, thermostat controls a contractor in the unit outside. The contractor starts both the compressor and the fan, and the capacitor is double poled with a fan side and a herm side separated by a common node. When the thermostat senses high temp it sends a high signal to the AC contractor that closes and applies 240V to the compressor and the fan. The run capacitor is needed because the machine does not have a neutral and acts as running storage while the machine is running to save energy (opposed to dumping it through the neutral to ground.)

The capacitor is run sized to be efficient, and cant be too big or it will sag the voltage. It cant be too small or it will not store enough energy to help start the compressor. As the machine ages or even in some new high efficiency machines the capacitor is just barely able to start the machine. Adding a hard start with drop out relay is the best option. Gives the capacitor extra kick to start, drops out when it is running to maintain system design parameters. They make a 2 wire kit that is just a piggy back capacitor, but you do not want that. You will want a 3 wire kit with the relay so that it drops out after the machine is running.

Here is the tricky part that happened to my machine: The capacitor can short out and still work. Mine reads 0 ohm from common to fan terminal, and OL from the HERM to common. This means that the fan side failed, and the HERM side was still good. But common is tied to ground, and the capacitor had 240 across it. So what happened is the compressor started fine, and the fan ran half speed backwards. Half of the voltage for the fan was shorted out through the capacitor and caused the fan to run on 120V in the wrong direction. I talked to several HVAC techs that I work with and they all confirmed that they had seen that happen but did not know why.

So if your unit is running and will not shut off, it is probably the contactor. They can be bought for $10 on amazon or Home depot had some last time I was looking for one. If the unit fails to start or runs poorly check the direction the fan is turning, it should be blowing air straight up and out. If it is running backwards, I would replace the capacitor and check the wiring to make sure that it was wired correctly. My machine has the internal wiring diagram on the inside of the panel that covers everything. Adding a hard start will not hurt the unit, and will significantly drop your starting current that is tripping the main breaker. Just watch a few youtube videos, and make sure that you are using the machine disconnect AND opening the breaker at your main board. Use the same size contactor and capacitor that your machine came stock with, and add a hard start if you are having issues with it starting. Also know that capacitors store energy and can easily kill you if you do not discharge them before working on them even if power has been turned off.

One final note, when I opened mine there were two big ass wasp nests in there that had gummed everything up and was quite the surprise when they were ~12" from my face when the panel came off.

Hope this helps.