The thermostat sends a 12 volt signal [typically] which triggers a relay in
the outside unit which connects 220 volt lugs to run the compressor pump
and the cooling fans for the outside condenser.

Very often, the symptoms which you describe, happen when the 220 Volt
contacts become worn from arcing on contact and then "stick together".
Another thing that happens is the springs that force the contacts apart
when the thermostat signal says "disconnect" become weak and the contacts
stay connected..

It will of course cause your compressor to fail from overheating after
running for hours while you are away from home [don't ask how I learned

I suggest it's a good time to call your local AC company for a service
call, if you don't feel comfortable addressing it yourself..
If you do.. pull the service disconnect prior to opening anything
electrical and of course be sure your unit is not going to kill you.

Good luck


On Tue, Aug 4, 2015 at 8:34 PM, Kaleb C. Striplin via Mercedes <> wrote:

> So the inside unit has been running a while but outside unit not, its at
> set temp of 73.  It turned off a minute ago for about 1 minute and now has
> turned back on again.  Thermstat says its calling for cooling and outside
> unit is running.  Will see if it turns off in a few minutes
> On 8/4/2015 10:18 PM, Kaleb C. Striplin via Mercedes wrote:
>> A couple of weeks ago I noticed the blower would kick on at random on the
>> house ac unit even when it did not call for cooling (outside unit not
>> running just inside unit).  Sometimes it would run for 30 seconds then shut
>> off.  Sometimes when it does call for cooling when its done it will shut
>> off then a couple of minutes later the inside unit will kick on.  I was not
>> sure if this was some sort of feature or what.  Anyway, last night I
>> noticed it was starting to get cold in the house and it had been blowing
>> for a while.  Thermostat was set to go to 73 at night.  It was 71 inside
>> temp indicated in the thermostat which was below the set temp. The outside
>> unit was running but it seemed to be stuck.  Not sure if it is a thermostat
>> issue or some sort of control board issue on the inside or outside unit.  I
>> turned the thermostat off and it continued to run.  I even actually removed
>> the thermostat from the wall base plate so it was not connected and it
>> still ran. Question is, should it not completely shut down if the
>> thermostat is removed or if the stat was stuck in cooling mode and sent
>> signal to the unit to turn on, will it continue to run until a signal is
>> sent to turn it off so in other words even with thermostat removed it is
>> not sending the off signal?  I ended up flipping the breakers off for a
>> minute then back on.  I am thinking the outside unit did not come back on
>> but the inside unit did and blew for a while then eventually shut off.
>> Sitting here right now I am thinking I am having the same problem. I just
>> cant figure out why it seems to only do it at night.
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