Fifth Wheel Cooling Questions

[Rick & Janet]

We sold our sticks and bricks home and are now living full time in our fifth wheel so we can get it ready and get use to living in it. Will start traveling in January of 2017. First concern is the cooling step up. We have two Dometic air conditioner units. Is it normal for them to be tied together with the ducting. The rear unit will come on and run all day because it is trying to cool the entire fifth wheel. Front bedroom and bathroom will get a lot of air from the rear unit and is cool and the front unit will not come on.

 

Any advice, can I separate them so each unit cools it's own area.

 

Than you,

Rick

[BigTexRex]

Don't separate the ducts. I will turn down the front AC to a lower setting to help cool the downstairs...that helps tremendously.

[edatlanta]

I have 2 ducted a/c's feeding the the same duct as well each with it's own thermostat. I have found keeping the rear unit set 1 degree cooler at night than the front and 2 degrees cooler during the heat of the day day keeps the two in sync. They both cycle on/off periodically vs one of them running all the time.

[Kirk W]

Two air conditioners feeding into the same duct system is pretty standard in the RV industry. Probably several reasons but few if any of those reasons have anything to do with better cooling for the owners. One reason is probably that many RVs have a single a/c with the second one optional. That way they are all built the same way. It would be difficult to separate the two systems and even more difficult to do so in an effective way without destroying the ceiling of the RV, since the duct-work is installed during the construction of the RV. In most RVs the a/c in the bedroom area is a smaller size and is intended to be secondary/supplemental to the main unit.

 

The air outlets are probably adjustable so that you could close down on those in the bathroom area and open those in the living area to cause more of the air from the rear unit to feed into the living area, which usually happens naturally since they are closer to the rear unit. Even in a motorhome there is often that same effect, even though the bedroom is at the same level as the living area, partly because of the living area being so much larger. In really hot weather it becomes very difficult to balance the load so we found that it helped a great deal in our motorhome to keep a fan running in the bedroom area, blowing down the hall toward the living area. Even then, the living area a/c always operated much more than the bedroom unit when in very hot locations.

[WeBeFulltimers]

We also have two units feeding the same ducts and like it that way. We minimize the noise when only 1 unit needed by running the unit that if farthest away from us at the time.

[Rick & Janet]

Thank you for all the replies, will work on adjusting thermostat and see how that works. My air outlets are not adjustable so I might look into replacing them if I can find them.

 

Rick

[travelinbob]

Our 2006 has a A/C for the downstairs which also cools the toilet room. The upstairs A/C cools the bedroom and they are not ducted together. Most of the time the downstairs one is enough. In warm temps we will run the bedroom one an hour before bedtime. A week or so ago we had 100 degree temps and used both at the same time and we very comfortable but we have 3-1/4" walls in our 5er.

[budeneighe]

We also have two units feeding the same ducts and like it that way. We minimize the noise when only 1 unit needed by running the unit that if farthest away from us at the time.

Same here. One key may be whether you have a "balancing" thermostatic control for the 2 A/Cs. Newer unit have some sensing and controls that automatically shift / alternate the A/Cs to reduce simultaneous power use as well as focus more temperature control to the area it is needed. One thing that is often overlooked is return air flow and the location of the thermostat(s).

 

Return air flow can be inadvertently blocked by closed door between compartments. In some cases, this can also prevent the return air from passing by the controlling thermostat so it is not really sampling the temperatures that are really needing to be controlled.

 

I replaced our "dumb" Dometic thermostats with newer digital units that are also wifi accessible. They are also programmable into 4 periods a day and with a little understanding and planning, can generally swap off the main duties over these different day and night periods. The wifi accessibility makes it easy to change the temp setting from my cell phone, tablet or PC. Additionally, it has a radius awareness that can tell my location and if I am more than xx miles from the RV, it will switch the operating unit to an "AWAY" mode that keeps it at a more conservative temp until I am getting closer to it. This saves energy while I am away but when I am headed home, it gets things back to my comfortability settings. It is also nice to check on the temps when the dog is left at home, just in case I may need to adjust it or have someone check on her.

 

The big issue in adequate control, though, is about controlling where the air moves and to be sure the thermostat is calibrated for any temperature offset of its location from your normal location in the RV.. And BTW, be sure that the hole in the wall behind the thermostats for the wiring, is well sealed over otherwise, it may be responding more to variances in air being drawn out of the wall than about what is in the open living spaces of your home.

[Smitty77_7]

On Class RV's, and many Fivers too, another reason the Living Area (Front for RV, and usually Rear for Fivers) have higher AC demand is the increase in windows. Especially so for Class A's RV, where the single greatest heat gain, and conversely loss, is the front windshield.

 

Our 40' coach has two 15K Dometic Penguin Roof Mounted AC units. Ducted, and the ducting vents do have registers.

 

We use different techniques based upon different times and weather conditions:

 

- In mildly warm weather, we use whichever AC is furthest away from where we are. For example in the early evening, we'll run the rear bedroom unit. Closing off all registers, including two we have in hour shower/bathroom hallway. This forces the rear AC cool air out thru the front living area of the coach registers. Reducing the noise significantly for TV or Stereo usage.

 

- Bed time we'll reverse the AC units, and modify the registers accordingly

 

- In hight heat conditions, where one AC can't handle the cooling demands, we'll still set the AC unit away from where we are on to the normal Auto setting. And set that zone 2-4 degrees lower then the area we're in. On the AC unit in the area that we're in, we'll set the fan to Low speed, and close the direct vent from the bottom of the AC grill. This reduces the fan noise quite a bit, and the other unit is still cranking out maximum cooling. And like Kirk, we'll use a small fan to push air from the AC zone running on Auto (Full force.) to the area we're in.

 

- If in extreme heat, say 110 and above, we'll run both AC's on Auto (Full force.), and have all vents open. And, we'll move the fan into the room that we're in, and put it on rotation. (Careful on this, as if it is a Class A with the big windscreen, and you do not have an external cover, and or the internal reflex-it type protection (Or some other insulation.) - this could introduce more heat into the area.)

 

- If on 30 Amp supply only. We sometimes close off the door from front part of the coach to the rear, to reduce cooling demands and one the one unit in the area we're in. Shifting about 20-30 minutes before we change locations for the night.

 

In addition to AC and fan usage. We maximize awing usage on all windows. Will case inside blinds on the side that the sun is hitting. Etc.

 

A search of the forum will show some great threads on heating and cooling tips... I learned lots from those threads from many of the veterans that share their knowledge so generously...

 

Best to all,

Smitty