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Old 09-21-2013, 01:50 PM   #1
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Installing 3rd A/C Unit

We have a 2010 Fleetwood "Discovery" 40G that we love dearly. However, during a recent trip, it's become clear that having only 2 A/C units simply won't properly cool the rig. The front 2/3 of the RV cool fine, but keeping the rear bedroom is a nightmare.

Just how much of a hassle is installing a 3rd A/C unit? Will the Onan 8500 "Quiet Diesel" handle 3 units?

Any advice appreciated.
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Old 09-21-2013, 05:57 PM   #2
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I am certain it can be done. I can't say how because your location has to be chosen very wisely and consideration must be made for what is under the roof skin in terms of wires, roof ribs and other things that the manufacturer may run in the ceiling. Our 7KW handles the three A/C units we have with no problem. Our only complaint is the noise generated by the A/C units and that seems to be normal.
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Old 09-21-2013, 06:08 PM   #3
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Quote:
Originally Posted by Herman Snerd View Post
We have a 2010 Fleetwood "Discovery" 40G that we love dearly. However, during a recent trip, it's become clear that having only 2 A/C units simply won't properly cool the rig. The front 2/3 of the RV cool fine, but keeping the rear bedroom is a nightmare.

Just how much of a hassle is installing a 3rd A/C unit? Will the Onan 8500 "Quiet Diesel" handle 3 units?

Any advice appreciated.
Typically, you have to give up one of your ceiling exhaust fans. That fan location is normally the same "hole" as an A/C. However, you'll need to check the roof for A/C clearance to other objects. The fan is 12vdc so that connection is already there. 120vac may or may not be easily accessible. You may need to run another line with a circuit breaker. If you are planning on using your existing thermostat it needs to be capable of controlling 3 units.

BTW, your failure to keep the bedroom cool is a little unusual. It's more often the front because of heat load at the windshield.
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Old 09-21-2013, 09:42 PM   #4
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Our Fleetwood I just adjust the vents as in closing some up front and lowering the thermostat in the bedroom. Both of my ACs are ducted together. Works great for us as both AC units are up front and keeps the bedroom quiet.
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Old 09-21-2013, 11:15 PM   #5
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When I checked in at the factory for a third one in the rear I was told the roof was not strong enough to support the OEM style that they put it when it was built.

I can cool to the high 70's in a black top driveway at low to mid 100 temps so I live with it.
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Old 09-22-2013, 09:35 AM   #6
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BTW, your failure to keep the bedroom cool is a little unusual. It's more often the front because of heat load at the windshield.
The two units are in the front half of rig. What that means is that ductwork for the front unit only runs about 4-6 feet whereas the rear unit has to run 14-18 feet to get to the bedroom.

Wonder if I could just put some kind of booster fan in the ducts blowing towards the rear???
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Old 09-22-2013, 09:42 AM   #7
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I've read a number of reports where people have added a third rooftop AC unit, or just added a single rooftop unit to supplement their basement air.

In each case I read, they removed one of their ceiling vents and the AC was a perfect fit. Running the proper 120v wiring to the ceiling was the biggest challenge.

Good luck
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Old 09-22-2013, 12:38 PM   #8
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If you have an available vent your willing to sacrifice, remove the 4 screws that hold the plastic trim on from the inside of the coach and see if the opening is pre-wired for a 3rd ac. It should also be obvious if the opening is reinforced for a AC unit.

I did this on a 5er I owned at the time. Mine was pre-wired, so all I had to do is remove the whole vent assembly from on top of the roof, clean up all the caulking, place the ac unit on top with a foam seal in between and tighten the bolts that hold it in place, connect the wires, and attach the plastic cover on the inside of the coach. I went with a down draft with controls on the unit, so I didn't have to mess with ducting or thermostat.

The hardest part was getting the ac unit up on the roof.

Best of luck!
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Old 09-22-2013, 01:23 PM   #9
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Call Fleetwood Customer Service give them your coach build number and get their opinion if it is doable or not.
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Old 09-22-2013, 03:29 PM   #10
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Have you verified that both units are performing to spec?

Is a higher capacity unit than the factory model available in the same form factor?

As mentioned earlier, partially closing the forward vents should help to balance the air flow.
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Old 09-24-2013, 04:12 PM   #11
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You may need to check your ducts. I had issues with my ac not cooling the unit evenly. I had 2 big holes in the duct work that bled off a lot of cool air. Pulled the shrouds, and looked in with a mirror. Patched it up with foam, and great stuff from Home Depot. Combination of closed, and open vents keeps the unit cool. My RV is only a 30', but I'm in Southern California.
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Old 09-24-2013, 04:16 PM   #12
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Cold air falls, Hot air rises?
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Old 09-24-2013, 04:35 PM   #13
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Cold air falls, Hot air rises?
Yes, unless you are RVing in Australia. Somehow related to which direction the toilet water swirls.
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Old 09-24-2013, 04:35 PM   #14
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Cold air falls, Hot air rises?
Yes ... but I'm missing your point. Ceiling ductwork, if not intact, bleeds the cooled air directly into the ceiling between the interior finish and the roof.
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