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Author Topic: Roof air conditioners  (Read 3828 times)
wal1809
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« on: May 23, 2010, 03:10:48 PM »

I know nothing about them other than When thy blow cold air they are out of sight and out of mind.  When they don't blow cold it irritates me, severely.

On the way home from the hill country we got hot.  I have three Ac units and they should be able to keep up.  When I first bought the bus they would get so cold it would run you out of there.  Now they need attention.  The middle air is dripping water inside so we turned it off.  I don't think the other 2 are stoking as good as they should but they certainly could nit keep up with the heat we had today.

Does anyone have a recomendation for a good roof Ac repair guy in the Houston area.  I am only guessing but I figure the big chain Rv places like HD world will hammer the pocket book.  Luvrbus I hope you have an in for someone around here.
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mcichad
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« Reply #1 on: May 23, 2010, 03:21:50 PM »

Hi, if your middle unit is dripping inside then it sounds like the drain may be plugged, not allowing the water to run out it's regular drain.  Sometimes you can simply remove the covers and use a hose to wash them out, like the condenser and unplug the drains, possible dirt/dust build up, washing only the condensor, electrical doesn't like water;)  When this happens, the evaporator can't dispate humidity and therefore freezes, cooling will stop until the evaporator unthaws and then the cycle starts again, so cooling is very much limited.

The condensor which dispates the heat is mounted on the roof, the evaporator will be lower cycling the air from the inside of your coach through and blowing out cold air, which the hot is dispated out the condensor.  Using mild compressed air you can blow through the condensor fins to remove debris.

Hope this helps to stay cool:)
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wal1809
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« Reply #2 on: May 23, 2010, 04:47:33 PM »

Alright!!!!  I am going to ge up there and check it out.  In the meantime if anyone has a place for me to take post it up if you please.
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luvrbus
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« Reply #3 on: May 23, 2010, 05:01:32 PM »

Wayne,when I had roof airs on my Prevost I had the best luck and prices at a place in Channelview it is called Channelview Supply on I 10 at the Dell Dale exit east of Dell Dale on the feeder about 1/4 of a mile.
I would think PPL on the south side of Houston would be best for you it is also a good outfit prices are a little higher than Channelview. 


good luck

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wal1809
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« Reply #4 on: May 23, 2010, 06:40:17 PM »

Thank you Luvrbus.  I work right down the road from PPL.  I will take it there in the morning.  I looked at the drain hole on top from a ladder.  I could see through it.
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« Reply #5 on: May 23, 2010, 10:21:41 PM »

You need to find out why there is water dripping inside.  The condenser uses that water to help the efficiency and it can make a big difference in the AC performance.

Take this to the bank.....remove the inside shroud and run on high cool.  That's like getting a half AC unit for free.

Your ac unit should drop the temp of the sir that goes thru it by so many degree.  In a hot soak it drops the temp the same as when it is running on a cool coach.  Measure that drop and consult with the MFR rep. That is the only way to be sure the unit is doing it's job and just isn't overloaded with heat.

Some people can get by with one unit when parked but they barely make it with three running full tilt if they are doing 60 mph down the road.  That tells me two things....their insulation is pretty good and they have a ton of air leaks that only come to bear with  air pressure differentials causing flow and allowing heat to permeate.

Wash the outside condenser fins with a strong garden hose and some spray detergent in a bottle.  That water should run off the roof and present no problem.  Drop the shroud and spray some detergent on the fins with a garden sprayer.  Then rinse the soapy stuff  off with the same garden sprayer.  The water running off of the evaporator coils should be ducted outside exactly as if it were condensate.  When you are done with that you will have either fixed your problem or eliminated dirty fins as the source of your grief.....er, heat.

I have read of Knuts with MCI's that had over heating problems with the engine.  They solved the problems by using a ca washsoap sprayer to wash the "mud" out of the rad.  $5 fix for a really nasty problem that may solve with thousands thrown at a rad replacement.  MCI isn't the only rad that sucks air through it and gets dirty s why isn't this a "annual PM".

John full of questions.
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wal1809
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« Reply #6 on: May 24, 2010, 08:00:55 AM »

John I do believe you are hitting the nail with the hammer.  I dont have trouble cooling  while parked somewhere with the front and the rear ac running.  We have just been leaving the middle one off.  As we go down the road the (what I believe) lack of insulation allows the heat to creep.

This is a problem as it is just now getting hot enough to make a difference.  Later if left unchecked (the insulation issueor not cooling) I won't be able to drive the bus.  It would be too hot.  Since I did not do the conversion there is really no way to know what they used for wall insulation unless I peel back a wall.  I do know the sub floor is plywood and the top floor is hardwood.  Stapled to the plywood underneath is bubble wrap. 

I can start right there and put 10 inch foil backed styrofoam board attached to the plywood in the top of the bays.  Get my fins cleaned in all ac units and find the leak in the middle unit.

I did put a thermometor in each unit and the air temp coming out of each was 55 to 60 degrees.  Outside temp was around 90.
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wal1809
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« Reply #7 on: May 24, 2010, 08:02:23 AM »

Update.  Dropped it off at ppl.  Sometimes you just got to call in some help.  I got enough going on.  They suspect as yall did.  Either the drain is plugged or the seal twix the ac and the bus is broken.  We shall see.
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wal1809
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« Reply #8 on: May 24, 2010, 10:34:10 AM »

Latest update!!  PPL called and the seal twix the ac unit and the roof was bad as well as the thermostat.  With that one kicking on all cylinders and the other 2 we should be back to cool again.  $300 bones aint too bad for parts and labor.
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« Reply #9 on: May 24, 2010, 10:50:22 AM »

Wal,

This was my main point.  By observing that when stopped you seem to have enuf AC tonnage you sorta prove that your insulation is at least barely adequate.  That means you don't have to start over with the conversion.  May not be as good as you want, or even as it should be, but it is enuf.

Some people can get by with one unit when parked but they barely make it with three running full tilt if they are doing 60 mph down the road.  That tells me two things....their insulation is pretty good and they have a ton of air leaks that only come to bear with  air pressure differentials causing flow and allowing heat to permeate.  Cause if you don't have any air GOING THRU a hole, that hole doesn't matter much.

About that AC tonnage and the air temp coming out of the unit.  Of course it would seem to be the very most significant data is that while at 90 degrees ambient you had 60 degree air coming out of the unit  That's interesting in many ways but it ain't the key point.  It might be 90 outside but what you want to know is "what is the temp change" ACROSS the system.  Temp into the evap coils vs the temp coming out.  That would be the temp inside the bus vs the temp coming out of the ac unit.  But only to eval the operation of THAT UNIT.  The first step was to determin if the ac units were doing as good a job as they could. You seem to have done that by determining that ALL had 60 degree air coming out.  Me thinks a delta of 10 degrees between them if they are all injesting the same temp air is an indication of serous degradation in performance of the one that can't pull the temp down.  I am  ignoring the chance that you have a 12,000 btu unit and a 18,000 unit side by side.

Think of this as a water flow and tank filing with water.  BTU's are how fast you can bail water out of a tank and the tank is your bus.  The heat flows into your bus thru the walls and windows and that will be so many BTU's under a certain circumstance.....say high noon in Aug, you are in the sun and the ambient is 100 degrees.  Gallons per hour of heat.  If the tank starts to fill, well, then, the volume of water stored is going up, and in this analogy, the temp in the bus is going up.  To hold the water level steady you need the two numbers to be equal...to cool the place you need to bail FASTER than the water is coming in.  To cool the place in a short enuf time to be able to use the bus the same day that you return home you need to be able to bail FASTER than the water is coming in.   If you get home after a long day of heat soak in the Az  sun at 120 ambient and the thing was NOT in the shade you are looking at 150 (at least) inside temp.  To get that down to 75 you will need some pretty hefty over kill on AC power if you want to do that in less than a couple of days.

Now so far in this tombe there aren't any numbers.  That means that at this point, Sean has puked three time if he kept reading at all and Nick's stomach is hurting from laughing.  But here is the real bottom line.  When you are done can you get the temp down to 75 in the sun with a ambient of 120?  If not then you can't visit Palm Springs or AZ in the summer or even drive thru in the day light under those conditions. Crunch all the numbers and figure till the cows come home but that is the bottom line.  You can use numbers if you have the lux of building and controlling the construction and then sizing the AC units but it still boils down to.....  White roof helps all the time, shades only when parked and "holes" only when in motion(mostly) and R factor rules.  You install the BTU tonnage that works for everybody else and you seem to have done that.... three units at 18.000 BTU each.  Three of the 13,500 units should work as well as it did before they came up with the bigger units.

Bubble wrap is scary.  What other brilliance remains hidden?  Spray foam the underside of the floor.  Does your wall that is facingthe sun feel warm to the touch all over or in spots?  The ceiling?  If you take one of those no touch temp guns and start shooting EVERTHING and EVERYWHERE while you are parked or running down the road....where are the hot/cold spots and by how much?  Those marker lights don't only leak water, they leak air, so R&R and use that sticky putty that the RV industry invented for every outside appendige.  Handi can spray foam all the cavities you can get to.

Every Pre and Hi Line has a couple of those str4ong 8 inch fans blowing on the driver.  Driving into the sun the driver needs the drivers air plus 70 degree ambient to tolerate the sun loading he is enjoying.  Only the 70 degree ambient(inside) would be enuff if he had enuf air flow across hisself at that temp.  I have heard many Knuts say that they installed a additional roof air over the driver or wished they had put the split where it would blow directly on the driver.  They are shooting for really cold air in one spot but they could very well be OK if they got a lot of cool air moving.  BIG fan!  Even in the winter, the driver may develop a need for cooling after he turns into the sun.

I read the following as a cry for HELP:

Later if left unchecked (the insulation issue or not cooling) I won't be able to drive the bus.  It would be too hot.


I read the following as needing more clarification as it is the WRONG conclusion.
As we go down the road the (what I believe) lack of insulation allows the heat to creep.

I really hope that you can get this under control.  As well, I hope I made a plus contrib.

Hope you keep us informed with your progress and findings.

John
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Bill B /bus
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« Reply #10 on: May 24, 2010, 11:58:57 AM »


"I did put a thermometor in each unit and the air temp coming out of each was 55 to 60 degrees.  Outside temp was around 90."

The delta temperature, in and  out, of the AC unit should be in the range of 17 to 21 degrees. Not outside to AC exhaust delta.

Good data but I can't find the source document. But then again, I remembered the data. Grin

Bill
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« Reply #11 on: May 24, 2010, 12:07:10 PM »

Clean your aircons.

Check and see if they are in the airflow -- if they are all mounted on the centerline, the two in back may be masked by the turbulence created by the one in the front.  Do you have anything else on the roof, like satellite dishes, which might be spoiling the airflow?

Check freon levels.

Replace belts (if any).

Check fan speeds -- you could have a cold unit with a slow-running fan.
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luvrbus
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« Reply #12 on: May 24, 2010, 12:07:40 PM »

Wayne's problem may also be that in Houston it has been over 90 degrees and the humidity is around 95% that will give any AC a workout trying to get rid of the moisture and cool


good luck
« Last Edit: May 24, 2010, 12:10:29 PM by luvrbus » Logged

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wal1809
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« Reply #13 on: May 24, 2010, 01:05:35 PM »

Hello Fellas.  Just picked her up.  PPL did a great job.  $204 and some change.  They replaced the seal and put a new thermostat on.  Worked fantastic.  Luvrbus thank you for sending me there.  I usually shy from large chains but I can't complain about the service at all.
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Sean
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« Reply #14 on: May 24, 2010, 01:26:34 PM »

...  The condenser uses that water to help the efficiency and it can make a big difference in the AC performance.
...


AFAIK, the only manufacturer ever to make use of evaporator condensate to improve condenser efficiency was Carrier, now out of the RV business altogether.  Neither Dometic nor Coleman-Mach do this, to the best of my knowledge.  Certainly the neither Penguins I have now nor the Colemans I had on my Fleetwood used the condensate for anything -- they just dumped it overboard through a weephole.

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