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Old 09-17-2011, 11:52 AM   #1
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Roof AC Noise when Driving

When driving (1998 MDSS) we often hear what sounds like a banging noise coming from the front AC, we recently replaced the shroud, but the noise was there before. I think that it's more prevalent when it's windy as if a flap was banging. We do not run the roof air when driving.

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Old 09-17-2011, 01:42 PM   #2
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Usually the shroud causes all the noise so make sure it's on tight. The mounting screws have a strong tendency to come loose. Otherwise, you might want to take the inside vent cover off and make sure that the long screws holding the AC unit in place aren't loose. This would mean that the entire unit is loose which is not very likely but worth checking. While you have inside vent cover off you might check for something else to be loose up inside as much as you can reach. MAKE SURE THE UNIT IS OFF!!!

Just some ideas ...

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Old 09-17-2011, 01:50 PM   #3
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You might try removing the shroud, then drive with it off to test. Could be an antenna, dish, or loose solar panel, too. Give everything a tug.
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Old 09-17-2011, 02:07 PM   #4
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The compressor is mounted on three rubber mounts on most A/C's. I have seen these rubber mounts come apart and I have seen the mount bolts break. I have also seen the tubing bounce and hit different parts. Also check the fan mounts they have failed and caused the fan to move too much. Just check the area very closely and look for a wear pattern.
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Old 09-17-2011, 02:21 PM   #5
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Are you sure that the noise is from the A/C unit. If you have a satellite dish mounted in front of the A/C, these have been known to make a lot of noise at highway speeds. It has to do with the wind flow over the front of the coach reflecting off of the front of the A/C and lifting the back of the dish from the roof, which again disturbs the air flow, causing it to bang back down again. The process is repeated ad-nausium. One cure is to remount the dish behind the A/C. Another is to ring the dish with 6" aluminum flashing using a piece of slit vinal tubing on the edge to protect the roof. This worked for me.
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Old 09-17-2011, 03:40 PM   #6
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I get a similar noise occasionally but put it down to the TV antenna. The roof transmits noise easily and it is hard to pinpoint the source.
John and Mary Knight
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Old 09-17-2011, 06:06 PM   #7
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If the internal inspection of the AC doesnt provide any issues--try the old crank-down TV antenna or the air horns--older models with the horn bells out on the front leading edge of the cab can catch the wind.
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Old 09-21-2011, 12:12 AM   #8
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I found the antenna cable to the crank up was flapping in the wind. Duct tape proved it. Now silicone holds it down.
Dan and Patty
"04" Alpine 34' FDDS
Saratoga, CA
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Old 09-21-2011, 12:16 AM   #9
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We sometimes get a banging noise also, think it's the satellite cable or the over the air antenna wire. Just haven't tried to fix it. Wife wants to go "camping" again soon so I may have a chance to try some duct tape.

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