High Country AC Vibration

[fun4rvn]

Hi everyone. My wife and I just picked up a 2013 Cougar High Country 329TSB about a week ago. We haven't done our inaugural camping trip yet but, of course, we have been all over it trying things out. It's starting to warm up in our area so, we ran the AC to cool things down. After starting the AC, we walked through the trailer beginning in the rear bunk area, through the living room and ended up in the master bedroom in the front of the trailer. Once there, we immediately noticed a pronounced vibration that was both heard and felt coming from the AC unit. I played around a bit with the thermostat trying just the fan on low (the vibration stopped) and high (vibration returned). We noticed that when we closed the master bedroom doors, the vibration was dampened significantly. It almost seemed similar to riding in a car with all the windows closed and then opening the sun roof and getting that buffeting sound that occurs. The vibration happens only in the master bedroom and no where else. There is only one AC unit towards the middle of the rig and no unit directly over the master. Any thoughts on what's going on and possible solutions are appreciated. Thanks!

[JRTJH]

Several things could cause that, the most likely are a loose wall or connection in the ducting. Take the vents off, use foil backed duct tape (NOT FABRIC) and seal all the vents so they don't leak air into the ceiling cavity. Next, take the inside grill cover off the AC. check the air duct box closely, make sure it is secure, the damper between return air and supply air is sealed well, and all air leaks around that box are taped with the aluminum duct tape, then check the 4 screws that hold the AC to the roof. They should not be tightened and torqued too tightly, but should be snug enough to press the rooftop unit onto the rubber molding ring without deforming it too much. In other words, the 4 screws should be tight enough the AC doesn't move around, but not so tight that it crushes the rubber gasket/molding.

Leave the AC ceiling cover off and turn the AC on, see if the vibration is reduced. Then install the cover and recheck.

You should have the "quick chill" ceiling cover, so if it is still buffeting, open the vents on the quick chill and go back to the bedroom to see if the noise you heard is gone. If it is, then the noise is in the ducting, if it's still there, it's the AC. If you can't locate the loose ductwork, take it back to the dealer.

Keystone does a lousey job of sealing the ductwork both in the AC and the furnace ducting, so to increase cooling and to prevent losing your AC air as well as your furnace air into the open cavities in your ceiling and floor, you need to tape and seal the ductwork anyway, most of us realize a significant increase in air delivery after sealing the ductwork. I'm thinking that should eliminate your buffeting problem.

[davidcyndi]

This might be totally out there but have you checked inside the unit on the roof and made sure there isn't a muddauber nest up there. That can give you a good vibration if they have built a nest on the fan or whatever.

[fun4rvn]

Excellent suggestions! Thanks so much! We will be tinkering with the trailer this weekend and I'll do some investigation and report back.

[chuck&gail]

If you are going to check under A/C shroud for mud daubers, a good suggestion IMO, use a broom while standing on a stepladder to hit the shroud. Muddaubers ARE wasps. You do not want to try and run off the roof with wasps in hot pursuit.

[therink]

[QUOTE=JRTJH;

Keystone does a lousey job of sealing the ductwork both in the AC and the furnace ducting, so to increase cooling and to prevent losing your AC air as well as your furnace air into the open cavities in your ceiling and floor, you need to tape and seal the ductwork anyway, most of us realize a significant increase in air delivery after sealing the ductwork. I'm thinking that should eliminate your buffeting problem.[/QUOTE]

X2 on this. On both of the brand new Keystones I have owned, I basically redid all foil taping at all ceiling vents and in the plenum. I found loose tape hanging where it shouldn't and triangular pieces of the rubber roof material hanging inside the plenum. I also closed off the excess runs of ceiling ducts with cardboard and foil tape beyond the fore and rear vent openings to prevent the air flow from getting trapped in the dead ends of the ducts. I believe this reduces resistance in the air flow making the system work more efficiently.