AC

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shearhawk

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Apr 4, 2006
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  Since it is more economical to run the roof air than dash air.  I am considering removing the compressor and plugging up the hose lines.  (It does not work anyway.)  Has anybody done this, would like to do it properly and do not want any adverse consequences?  It looks like the hoses is hooked to the transmission cooler, in front of the radiator.  1990 454 Classic Coachmen.

Thanks,
Randy
 

Ned

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The compressor should impose little or no load when the dash A/C isn't on and some day when the generator won't start and it's 100+F outside, you'll wish you had that dash A/C.  Also, removing the compressor will probably require a new belt and there may not be one that fits.  I would leave it alone and get it fixed.
 

Karl

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WADR, it may not be as simple as getting a shorter belt. The pulley and idler geometry may require the belt to be routed in a particular way to clear other engine components. Gotta go with Ned on this one. Also, the tranny cooler is usually built right into the bottom of the main cooling system radiator; the hoses you see are strictly for the a/c condensor which is only slightly smaller than the actual radiator.
 

John From Detroit

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I will add my voice to the "Don't remove it" chorus as well.

If the AC has dedicated belts that only run it, simply remove them

If the AC belts also run other things (Water pump, Alternator That kind of thing then rather than removing the compressor simply disconnect the wire that goes to it (Tie the wire end to it with string so you know which wire it is should you ever wish to fix the dash air) when that wire is disconnected the compressor is nothing more than an ideler pully on the system.

There should only be one wire going to the compressor.
 

tyefighter

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Bend OR
My vote is to get it fixed.  The AC also runs when you use your defrost.  On those rare mornings when the dew is heavy or heaven forbid frost, the defroster with AC works the best.

Mike
 

King

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Where did you get the idea that the roof air is more economical than the dash air?  Even my small genset (2.8KW) uses a half gallon per hour at half load.  For a passenger car, the AC is so efficient that at highway speed, it is more efficient to run the AC than to run with the windows open with the added aerodynamic drag.
 

Gary RV_Wizard

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Where did you get the idea that the roof air is more economical than the dash air?

Most RVs get noticeably better fuel economy with the dash a/c off and the house air on. The house air system will cool the rig better (the dash a/c has nowhere near sufficient cpacity) and  a usualy uses about a half gallon per hour for the gen set.  The extra load of the dash a/c will easily equal or exceed that - the compressor can add as much as 30 hp to the power demand on the engine. Use of the house air also reduces the heat load on the engine radiator (a/c condensor is not shedding heat), which can be a help when climbing hills.
 

King

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Sorry, I don't believe that for a minute.  Each time you convert energy, you have losses.  When you convert gasolene to electricity with the genset you have one more conversion.
 

Jeff

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King said:
Sorry, I don't believe that for a minute.? Each time you convert energy, you have losses.? When you convert gasolene to electricity with the genset you have one more conversion.

King:

My 330 Cat gets 9.0 mpg w/o ac on, 7.5-8.0 with chassis air running. In an hour my diesel generator uses .4-.5 gallons AND cools the entire coach. The Cat also runs cooler without the ac on. We save at least .5 gph, run the generator which usually does not get enough use, remove some load from the Cat, and are more comfortable.

Our last coach was a Pace Arrow with a 460 Ford and the savings were still .5 gph and the Ford ran a lot cooler on hot summer days.
 

Just Lou

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Dec 25, 2005
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I have to agree with the majority here. ?I did what shearhawk suggests once as an emergency measure on a pontiac sedan with a siezed AC clutch ( put on a shorter belt and bypassed the compressor). ?I would NEVER suggest it as a fix for an RV.
 

BernieD

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King said:
Sorry, I don't believe that for a minute.  Each time you convert energy, you have losses.  When you convert gasolene to electricity with the genset you have one more conversion.

King

And how do you think the dash A/C gets it's power ??? ??? ???
 

King

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In the dash AC you have shaft horsepower directly turning the compressor.  For the roof unit you have shaft horsepower turning the generator to create the electricity, and a compressor motor turning the shaft of the compressor.  The losses are heat generated in the generator, motor and wiring.
BTW a dash AC uses less than 5 HP from the engine.  1 HP into the compressor equates to 12000 BTU cooling.
 

King

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:-\ correction;  The horsepower to BTU conversion was a tad optimistic --  It should be around one horsepower to 3750 to 7450 BTU depending on the AC efficiency.  The first must have been a website trying to sell AC units with HP ratings------
 

Gary RV_Wizard

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Sorry, I don't believe that for a minute.

Suit yourself, King, but actual measurements  beat theoretical calculations every time.  Even with the losses due to cpower onversion, measured results show that the genset and house a/c will beat the dash a/c in most motorhomes in both fuel efficiency and cooling efectiveness.

For one thing, small engines are generally more fuel efficient than large ones, so the fuel cost of running a genset is small to begin with. For another, the engine shaft horse power is NOT direct-driving the a/c compressor - there is a belt and pully system pplus an electric-operated clutch in between. Belt drives are anything but lossless and the dash a/c systems themselves aren't all that efficient as cooling systems go.
 

John From Detroit

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Your Motor home may have up to 4 cooling zones.. The DASH AC cools the "Cockpit" zone, (Driver's and passanger's  seat and a little bit behind them) no way does it reach all the way to the rear of the bus. The rooftops cool,, Well, the entire bus.  THus running the generator to run the roof top does a better job of cooling

Next is fuel economy.  My Genset is a 5500, that makes the engine around 10HP, at full draw it's about 1gal per hour if memory serves (I have the chart here, that may be half draw)  at idle it's about 1/2. However the engine AC is never on at half (yes I know you can adjust the temperture but the AC is either ON or OFF, no half about factory AC,  Dealer AC on the other hand cycles on and off)  I have found that extra power up front (Mine is a frount engine rig) means more gas millage believe it or not so taking a few HP off to run ac really cuts the millage.

Another factor,,, Someone said smaller engines tend to be more efficent... Don't know about that but I do know this, the engine on my ONAN is supposed to turn 3600/N RPM (Where N is likely 3 but may be 2) This really is etched in stone (Silicon to be exact, the control board for the generator) any faster or slower and things work, funny.

The engine on the MH is designed to work at many speeds.  A constant speed motor is far more efficent, cleaner too
 

Rex

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Alabama Gulf Coast
Just a work of caution to all.  If the dash air is not run periodically, the seals will dry out in the compressor and it will leak.  Recharging will not cure the leak, but repeated operation of the compressor will sometimes cure the problem.  If the leak continues, the seals just did not swell enough and will need replacing.  Even if you run the House Air, turn the dash air on while running for at least an hour or so.  The dash air should be run each month when in storage, even in winter, to prevent seal leak.  Do this when you exercise your generator.  I know you don't need air conditioning in the winter, but it will help you have it in the summer. 
 

King

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Small engines are not more efficient than large engines.  The opposite is true.  The most efficient internal combustion engines are huge diesels designed to power electrical generators for peak generation which actually are about 60% efficient.  The difference which is confusing is the fact that a large engine running at 20% burns a lot more fuel than a small engine with the same power output running at 90%.  Since most automobiles when maintaining cruising speed only use a small percentage of their maximum horsepower, a smaller engine will almost always provide better milage.  (Unless, of course, the vehicle is seriously underpowered, then all bets are off).  If you are powering a six ton behemoth down the highway, you are probably actually using over a hundred horsepower to maintain sixty miles per hour.  Taking off five horsepower from the engine for air conditioning would be expected to increase fuel consumption maybe a little more than five percent.  But then, running the on-board genset at point five gallons per hour also increases fuel consumption more than five percent.  If you are doing what we all do, to find what our best milage can be, we turn off all accessories and drive carefully to save fuel, we use less fuel.  But to then say that all the fuel saving can be blamed on the dash air is just plain wrong.  In my class B the MPG can vary from 12 to 15.  I can usually get the 15 by keeping the speed at 60 or below, and slowing on the hills to prevent the transmission from downshifting until about 45 MPH is reached.  In practice  I measure milage with each tankful, and the difference between running in cool weather and running in hot weather with the AC on is less than the difference between successive tankfuls.  I haven't run with the genset powering the roof air because I just added the genset this winter.
 
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