How cool does your motorhome get inside?

FrontRangeRVer · 07-28-2006, 12:17 PM

97 degrees outside, and our 36' unit with 3 slides inside temp is 78 with the basement air. Seems warm to me

Seems like Winnebago undersized these basement units...

yeah...gone through all the check the duct stuff, both compressors running also...

How cold does your basement air get your unit?

FrontRangeRVer · 07-28-2006, 12:17 PM

97 degrees outside, and our 36' unit with 3 slides inside temp is 78 with the basement air. Seems warm to me

Seems like Winnebago undersized these basement units...

yeah...gone through all the check the duct stuff, both compressors running also...

How cold does your basement air get your unit?

TXiceman · 07-28-2006, 12:35 PM

If you are in a sunny location, that sounds about right. You can help the unit by putting up solar shades on the windows or the Reflectix.

To see if your unit is working as designed, let the unit run for abour 15 minutes minimum. Take the temp reading of the air entering the unit, then take the air temperature at the outlet duct closest to the unit. The air out should be ABOUT 20 dF lower than the air inlet. If you are pretty close to the 20 dF number it is working as best it can.

Ken

ronboc · 07-28-2006, 12:56 PM

Thanks, Ken. A good number to know.

Could you please elaborate a bit on the possible reasons why one would be getting more or less than the magic 20 dF? And what might be done about it?

For instance, I've heard that a partially-clogged filter would get you MORE than 20dF (which seems just the opposite to me), and that it's not a good thing to get too big of a unit because it won't cool properly but just keep short-cycling instead.

I want to do as much as I can to help keep mine going, and be ready to get the last bit of comfort out of 'em when they stop cooling as they should.

Thanks!
Ron

montanaB · 07-28-2006, 02:25 PM

I am also disappointed with the AC system in my 05 Vectra which is going bye bye very soon. On a recent 98 degree day the unit could only get the coach down to 79 degrees. In my opinion, basement air is not very efficient.

Greyhound · 07-28-2006, 02:46 PM

I am currently sitting in Altoona Iowa where the current temperature outside is 95. Inside temperature is: 78 on the air conditioner setting, on the other thermometer on the sink counter is 75. I have never had a problem cooling the coach. I do have shades on the outside of the front, side and living room windows and the wife rigged a curtain behind the driving area which reduces the amount of heat entering the coach through the front window. I do on a regular basis, change the filter and rinse off the fins on the A/C unit with a steady stream, taking care not to bend them.
Had a Chieftain, 39T same type of unit and again no problem. A little PMS goes a long way.
I have a 2005 38J, triple slide.

Bob

smlranger · 07-28-2006, 03:50 PM

I surely don't want to jinx my rig but recently we were in Richmond, VA visiting some family. The rig was parked on a street in full sun..not a speck of shade anywhere and the highs daily were 85 - 88. We had the rig on a 20amp circuit from the house so only one compressor was being used. I had no problem keeping the inside temp 74F during the hottest part of the day. I had both slides out and window awings deployed. Could not use the patio awning since it was streetside. Frankly, I was amazed.

Now I'd love to have a rig with FBP but I do wonder if the rigs with more white do better in full sun.

TXiceman · 07-28-2006, 04:56 PM

Ron,

You can see more than a 20 degree temperature difference (TD) if the air flow is restricted. Basically what happens is due to the reduced air flow and resulting load, the refrigerant side boils of less refrigerant. The compressor is a positive displacment compressor and all it knows is to keep pumping the same CFM (cubic feet/minute). Since there is less refrigerant being boiled off (or converted to vapor), the compressor keeps pulling from the evaporator. The pressure reduces and the specific volume of the refrigerant (Cu. ft/LB, thinner gas or more distance between the gas moludules) increases which fills the compressor volume. As the evaporator pressure lowers, the saturation temperature of the refrigerant in the coil is reduced and the air off the coil reduces in temperature.

The reduced air flow can come from a dirty filter, a dirty coil of a restricted fan outlet. You can also get a lower coil temperature if the unit is low on refrigerant, but in a sealed system, this is seldom the case.
You can also get the effect of lowering the air flow if you are bypassing air internally,,,chilled air is bypassed back to the inlet due to bad duct work or installation.

You need to remember that a large single roof-top unit is 15,500 BTUH (1 ton is 12,000 BTUH), so a typical large A/C unit is about 1.25 Ton. I am not sure of the BTUH rating of the basment units.

When comparing the unit capacity to a typical home unit, remember that a home is insulated much better than an RV, so it requires less capacity per square foot of floor area.

I hope this clearer than mud.

Ken

SargeW · 07-28-2006, 06:35 PM

My basement air works great. I have used it dry camping at lake Roosevelt in AZ, with the outside temps at 105 plus. The air kept the inside around 80. To me it felt like heaven. I don't need to hang meat inside the rig, just be comfortable.

I also compare it to a 26' TT I had, and a 31' 5ver, both of which I had bought new. Both had a roof air, and both were 15K units. The best that they would do was about 10 degrees below the outside temp. The basement air is a huge improvement.

RonP · 07-28-2006, 06:49 PM

Anytime air temp difference between outlet and return air is around 20 degrees be it in a residential/commercial setting or a RV,the unit is performing to design specs. An air conditioner that is designed as oversized for the area to be cooled will actually not perform as well since it will not run sufficiently long enough to perform its basic purpose of dehumidifying the conditioned space-the condensation resulting from the cooling process.
As previously stated,the insulation qualities of the average RV does not match that of a well insulated home so the ability of the RV unit to reduce inside temp much beyond 20 deg from outside temps ranging 90 deg and up is limited.

One thing to check is the ceiling outlets located around the thermostat-if one or more blows directly on it,that could cause the thermostat to be satisfied before the surrounding air has been sufficiently cooled.

Steve St · 07-29-2006, 03:00 AM

Well it's been 96 here in Massachusetts and I've actually had to turn my temp up as it got too cool. This is in my Journey 39k

Steve

NeilV · 07-29-2006, 03:54 AM

Just got back from a trip to Ottawa going through the 105+ degree heat wave in DC and temps got down below 74 and we had to ease things up a bit as the girls found it a bit too chilly. These are 2 ton units that work as 1 ton when EMS cuts in or there is only a 1 degree diff between the stat setting and the room temps.

Ptribbey · 07-29-2006, 05:20 AM

I hate hot weather, and our coach was like everyones in that with an outside temp of 95 the best we could do was 76-78. I tried running the engine and chassis air, and that helped but not the best way to handle it. We removed a vent fan in the galley an installed a high eff. 13.5K roof air unit. We can now maintain 70-72 degrees with an outside temp of 97. It is not a big deal to install a roof unit as the 14" X 14" vent opening is the same size a roof air uses.

cookie monster · 07-29-2006, 06:34 AM

If the outside temp is 95-100 and your inside temp is in the hi 70,s that is about as good as any of these rv,s are going to do. I find 78 on a 98 degree day very comfortable. I think the biggest help you can give to the coach is some type of sun restriction on the front window. We all know that there are plenty of things to complain about on these rigs but the temp in your rig only getting down to 78 on a real hot day just ain,t one of them.- John

Ed Gardiser · 07-29-2006, 06:47 AM

PTribbey
Have you ever checked the total amp draw when the basement air and now the roof air are all on ? Just wondering
Ed Gardiser
Escondido,Ca.
04 Vectra
87 Nissan PickUp
FMCA

Ptribbey · 07-29-2006, 08:33 AM

With the two basement airs running we are pulling about 26 amps. They make a high eff. roof air that draws something less than 10 amps for a 13,500 btu unit. We keep an eye on what "other" things we are running with all three airs running, i.e. we don't run the clothes dryer at the same time, etc. This set up works good. Be sure and get a "non-ducted" roof air. We got ours at Camping World when they were on sale.

ronboc · 07-29-2006, 10:05 AM

Ken & RonP -

Many thanks for the clarifications. Like I mentioned, I'd heard all these concepts/ideas before, but never a good explanation as to why it is what it is. Now it all makes a lot more sense.

And if I understand correctly, the actual outside temp doesn't make that much difference as the differential between inside return temp and vent temp, right?

Thanks again,
Ron

RonP · 07-29-2006, 10:32 AM

The inside differential is the best way to tell if your AC is performing as it should.

Good Luck.

TXiceman · 07-29-2006, 01:15 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ronboc:
Ken & RonP -

And if I understand correctly, the actual outside temp doesn't make that much difference as the differential between inside return temp and vent temp, right?

Thanks again,
Ron </div></BLOCKQUOTE>

No, the difference between inside and outside temp does make some difference. The higher the outside temp is, the higher the heat gain load on the coach will be and the more AC you will require to maintain a fixed inside temp.

But for gauging the performance of the A/C unit, the 20 degree air in/out difference is as good of a starting point as you can get without a lot of more expensive equipmenet.

As for cooling a coach in the northern USA vs. the southern USA, the solar load (sun intensity) if higer the closer you get to the equator. Lay a piece of metal in the sun in south Texas and in Maine. If you measure the temperature, the Texas piece will be hotter

So a coach in the southern USA will work the A/C harder than in Maine.

Ken

NeilV · 07-30-2006, 12:08 AM

Just wondering - most homes I've visited here in Tampa Bay Florida and in New England have their AC set between 76 to 80. Why is it such a problem if your motorhome maintains these temps but can't get down to 70 when it is around 100 outside?

A 2 ton unit draws close to 30 amps and has to be power managed and dropped down to 1 ton mode when the draw from other circuits requires. If you put 3 or 4 tons of cooling in your coach much of the time you would not be able to use it all at the same time even with a 50 amp service. Add to this the power problems with the brown outs that have affected campgrounds across the country and the related power problem posts about burnt out equipment and you could be facing a host of other issues with tripped breakers and various equipment losses.

I found a simpler solution on days when the mercury migrates close to 100. I put a reflective heat shade up on the windsheild before I close the front curtains. This cost less than $30. I may get some smaller ones for the side windows in the cockpit area also since the one on the windsheild has made such a noticable difference in the amount of heat that radiates from the cockpit area.

Regards,