I have 3 AC's on my motor home. All Coleman mach series with Atwood thermostat. When I bought the coach a year ago I was told the two front ACs had just been replaced and they are much newer than the rear one. They cool the coach great, but when they get close to the set temp they start making some awful noises. I am hoping someone might be able to listen to the noise and know what is wrong.https://youtu.be/KYH3oXGXoJs

Are you talking about the buzz noise or what sounds like rain or debris blowing around.Or the cell phone alert.

Buzz noise. Back ground noise is stapling papers together and filing and such.

Do all 3 make the same noise? Are you on 50 amp service? How long after that buzz do the units shut off? Doug

No only the two newer units do this. Yes on 50 Amp, but it will have on any amp or the generator.The buss noise is what cause the the unit to shut down, it happens the instant the noise stops.

AC issues need diagnosis | Good Sam Community

30sweeds
Explorer
Sep 30, 2018
I would say it's low voltage.Start at the power source and work your way in.
Rvpapa
Explorer
Sep 29, 2018
Wouldn't hurt to check the neutral feeds in the coach, including through transfer switch if you have on. Sounds like a bad connection partially opening the neutral when loaded.
Art
wa8yxm
Explorer III
Sep 28, 2018
Recommendation: DO NOT USE AUTO use HIGH.. NOTE this may or may not fix your problem but there is a 2nd issue with AUTO.

A/C's make noise. lots of it. even ducted "Quiet" ones are noisy

But if you set the thing on HIGH (Only affects fan speed by the way) your brain swiftly learns to filter and block much of the sound.. IN fact one of mine I actually CAN NOT HEAR after about 15 minutes and have to use other means to tell if it's even running. (The other one makes a different type of noise not so easily filtered).

This is why I run mine on HIGH.. Also when the folks a site or two over have a "Heated Disagreement" the White noise from the blowers keeps most of it out of your RV.. So long as they do not start throwing things and bouncing them off your walls.
3_tons
Explorer III
Sep 28, 2018
Wild Card wrote:
Are you talking about the buzz noise or what sounds like rain or debris blowing around.

Or the cell phone alert.

X 2
Freightguy
Explorer
Sep 28, 2018
dougrainer wrote:
Freightguy wrote:
dougrainer wrote:
Sorry, I meant to state AUTO/COOL. I would suspect one of the capacitors. Have you checked the upper capacitor box for shorted/burnt wires? Also, have you checked the MOUNT for the Condenser Fan. See if the mount and motor is loose or the mount studs have broken loose. Check to 120 FEED wire to the upper control box. Since BOTH units have the same noise, maybe the installer did not wire nut the Black and White 120 wires securely and they are arcing when the system has a higher amp draw. Doug

Doug I have checked all your recommend. THanks for that, but still no luck.

Something I am wondering is, the original AC units on this coach were model 47024-879. But someone replaced the two that giving me issues with model # 47224A879. Could this model have a control panel that is not compatible with my system and thus be causing the improper running of these two units?

Thank you!

The control panel/s stay with the unit. All you replace is the upper unit. The New units are compatible with the original control board. Doug
dougrainer
Nomad
Sep 28, 2018
Freightguy wrote:
dougrainer wrote:
Sorry, I meant to state AUTO/COOL. I would suspect one of the capacitors. Have you checked the upper capacitor box for shorted/burnt wires? Also, have you checked the MOUNT for the Condenser Fan. See if the mount and motor is loose or the mount studs have broken loose. Check to 120 FEED wire to the upper control box. Since BOTH units have the same noise, maybe the installer did not wire nut the Black and White 120 wires securely and they are arcing when the system has a higher amp draw. Doug

Doug I have checked all your recommend. THanks for that, but still no luck.

Something I am wondering is, the original AC units on this coach were model 47024-879. But someone replaced the two that giving me issues with model # 47224A879. Could this model have a control panel that is not compatible with my system and thus be causing the improper running of these two units?

The control panel/s stay with the unit. All you replace is the upper unit. The New units are compatible with the original control board. Doug
Freightguy
Explorer
Sep 28, 2018
dougrainer wrote:
Sorry, I meant to state AUTO/COOL. I would suspect one of the capacitors. Have you checked the upper capacitor box for shorted/burnt wires? Also, have you checked the MOUNT for the Condenser Fan. See if the mount and motor is loose or the mount studs have broken loose. Check to 120 FEED wire to the upper control box. Since BOTH units have the same noise, maybe the installer did not wire nut the Black and White 120 wires securely and they are arcing when the system has a higher amp draw. Doug

Doug I have checked all your recommend. THanks for that, but still no luck.

Something I am wondering is, the original AC units on this coach were model 47024-879. But someone replaced the two that giving me issues with model # 47224A879. Could this model have a control panel that is not compatible with my system and thus be causing the improper running of these two units?
marcsbigfoot20b
Explorer
Apr 13, 2018
Sound like lack of amperage/power.
If each one runs fine by itself, but issue happens when all of them are running.......
Freightguy
Explorer
Apr 13, 2018
ok so in the day since my last post the AC furthest to the rear (zone 2) has new issues. It will start normally blow very cold air for 20 minutes or so then the compressor shuts down and wont come back on again.

I opened it up suspecting a burnt out capacitor, but no evidence of any thing like that. All looked as it should on the inside. I checked everything Doug had memtioned as well.

The issue with the other two units would show itself as the inside temp got close to what ever the set temp was set at. Yesterday I tried to isolate the issue by only working on the middle or zone 3 AC. I popped that open as well, looked really good inside as this one is just about 18 months old. I ran it for a couple hours and could not recreate the issue. Then it got hot inside so I put all 3 on to cool the place. Once all three where on the issues started again. Zone 2 will only run the fan after 20 minutes, 3 zone cools the best becuase the compressor runs the longest before failing. Zone 1 compressor just went into the cycle of fan running, compressor starting, making the horrible noise (which is getting louder) and failing, then starting all over again. Running all three would not cool the motor home. Inside temp was 86, set temp was 77. Could not get the inside temp to come down even 1 degree. This is very mind boggling.
Freightguy
Explorer
Apr 06, 2018
Thanks Doug, I havent tried anything so I will put those on the list.