air conditioner has quit working

sunrisetosunset wrote:
our common (now about 12 years old with us being the original owners) roof mount air conditioner has quit working.

for some time now (about a year or so with us using the camper sparingly over that time) when put in cool mode at the wall mount thermostat it would come on fine but began to act up a little as follows:

when not actually running i would hear a humming sound coming from the roof area (air conditioner location ofc) but when temp required it to come on or i slid the control down i would get 'normal' operation of the ac.

however since i didn't feel the humming when not being ON was a good thing i would turn the ac breaker in the camper to off until i needed it again.

this went on like this until about a month or two ago when i noticed the campers ac breaker was tripping, but if i slid it down and back up again everything would go back to what i just described; hum when not actually running but run fine in cool required mode.

this past week it pretty much quit entirely when my wife turned it on as i told her to (slide the break down then back up and slide the temp control to what we needed) which she did and apparantly it worked as before but then when i went in the camper about a half hour after she had done it i noticed there was nothing from the ac.

no cool no hum. so i tripped the breaker back down and back up and got nothing. went outside to check power cord and my own personal pedestal power panel and breaker there was not tripped and all other electrical things SEEMED to be working (not that i actually checked anything but i DID notice that the 'house' fan was running normal (not the ac fan but a fan fan on the ceiling).

so i went and tripped the camper breaker once more and back up and heard the hum so slid the control to cool and nothing......tripped the breaker back down and back up and nothing not even the hum.....

any help in troubleshooting is greatly appreciated....i'm not THE best mechanic in the world but i do farm for a living and have to do a LOT of things around here and wear a lot of hats so i might be able tofigure it out with some guidance on what to check and where ....thanks in advance gary

Does the humming sound co-inside with A/C outlet airflow?

Sounds as if your wall mounted thermostat has a cool/off/(heat?) control switch along with an actual thermostatic temperature sensing (mercury?) switch.

Common arrangement is the switch in "cool" position directly controls the fan motor which is likely the humming sound you hear, and also "enables" the operation of the A/C compressor thermostat control relay.

Turning the thermostat switch from "cool" to off, or opening the CB, will stop the A/C "humming" fan motor.

Although it seems highly improbable it appears that some idiot has wired only one "phase" of the compressor motor power through the thermostat control relay. Most RV A/C systems use a capacitor start winding that is only engaged to provide an induction motor startup period.

With the CB and "cool" switch "on" and energizing only the start winding would be most certainly result in an audiable "humming" sound/noise that would disappear once the compressor motor actually starts running.

Or...Starting relay stuck closed?