Need new A/C units up top

[Devin & Amy]

We have 2 Dometic Penguin Lo-Profile roof A/C's. (13,500)
We would like to replace them with something that works better.
These units are not capable of keeping up with a hot day without freezing up.
I will be adding a possible third unit to keep up, is there a way to wire in a thermostat/powershare system on rooftops?
We don't have the bayspace for a basement unit. And we have one fantastic fan 2/3 of the way back.
Thanks.
Devin

[skipn]

Devin,

  They do make a 15000 AC roof top  Maybe they will do

The following is a link to all there roof top brands   Check it out there are many choices.
http://www.dometic.com/f0493afb-4b19-459b-9a70-a6532be76248.fodoc
  Some are wall or remote controlled

If you just need a boost maybe the 12v units are worth looking into (from the truck side of there site)
http://www.dometic.com/enus/Americas/USA/Truck/HVAC-Solutions/

   YCoolingMV

    Skip

[jjrbus]

I watched a man replace what may have been a good A/C unit becuse the coils were plugged with dirt.  Not saying yours are, but a good cleaning (requires removing outside cover) may save a couple $$$$ My service manual suggests doing this once a year.  The dirt collects on the intake side of coil. On my units this is above the filter (cleaned filter lately?) It can be blown out from the outside with compressed air. Set something up to catch the mess inside!!!!HTH JIm.

[Nick Badame Refrig/ACC]

Hi Devin,

You could upgrade to the 15,000 btu units as said above. However, with 6 of you in the bus, I would go with a third unit

if you have the power provisions.  Maybe you could try the third unit first before you replace the two and see what that does for your needs.

If you need and priceing, just let me know.
Nick-

[Dallas]

After doing maintenance at a campground with about 28 camp trailers, all with roof air, I have to agree with both Jim and Nick.

I don't know a lot about HVAC, I'm barely capable of adding Freeze12 to a car system, however, the biggest problem with freeze-up and non-working roof air that I had to deal with was the rental campers who never cleaned out the intake coils from inside the camper. Those pieces of foam "Filters" are a joke. they allow so much crud through that they are nearly worthless.
I would estimate that 80% of the A/C problems were due to dirty fins. The other 20% was a problem where we actually needed to pull the unit, or have the RV guys come in and fix them.

My method of cleaning the coils was to cover the entire inside of the camper with cheap painters plastic, then take a long, flexible air gun and stick it up inside the hole and have at it. It's amazing how much more efficient the thing will work after.

Good Luck,

Dallas 

[boogiethecat]

I agree with Dallas... if you think about it, if your system is freezing, it's definitely working, and the problem isn't that your compressor  is bad, or the outside condenser is dirty- if those were an issue it wouldn't be freezing... instead it's that not enough air is getting by the cold parts (evaporator) to keep ice from forming.  That's not necessarily the fault of the AC unit, instead it's probably dirt inside the unit or a clogged filter.

And a third unit may be the answer... however  experience with my bus (one 13.5k and one 15k size) is that on a hot desert day with a bus full of people out in the 110 degree madness, they're fine.  The BIG trick to this is having the roof foamed with at least 3" of insulation.  That works MUCH more effectively than adding more AC units.  And of course painting the roof with reflective white...

Cheers
G

[jjrbus]

Well DuH, color me a senior! If its freezeing it must be working!!!!!! Which gives my addeled brain another moment of activity. Are these units ducted? Did they ever work right? Like Dallas, I am not a HVAC guy, but I have seen some poorly designed duct work. 

[Lin]

I'll chime in agreeing here.  If it freezing, it's most likely and airflow issue.  I once had a van with an after market system that had a constant problem with freezing coils.  That turned out to be because someone had sized the compressor to big and the evaporator to small.  However, the roof airs do not have that design issue. 

[Sojourner]

I assumed this was installed properly with or without proper designed duct system. Had no problem until now.

I assumed that inside room to cool is at least 65°F or warmer. Otherwise it will ice up. Same applied to dehumidifier...whenever under about 65°F. I have been there & learn that.

I assumed that it Freon is full...up to spec.

It likely you have a partial plugged evaporator or fan blades or squirrel cage is dirty or reduce speed or whatever to cause restricted designed air flow. Warmed inlet air flow need to be flowing high enough to keep evaporator from getting below 32°F or lower.

BTW...It important to keep from freezing outside of evaporator to avoid costly compressor replacement. If you don't here the clattering noise from compressor, then it should be OK so far.

Here a link:
http://www.hvacoracle.com/cgi-bin/publish.cgi?p=100&x=articles&s=cooling

FWIW

Sojourn for Christ, Jerry

PS..Dr Hall of MSU in 1958 was my teacher on industrial refrigeration system. Very interesting and learn the basic.

[JohnEd]

I'll add my vote to those that advised you to clean the coils you can access from the inside only.  The evaporator coils.  Here is another point....if it is a ducted system it is not handling as much air as it "should".....bad design possible but they all, by definition handle/flow less air than an unducted system.  If it isn't ducted and you want to increase the air flow and "apparent" BTU just take off the interior shroud and let it exhaust straight down.   Much more air flow that way.  Just something to try till you get a real fix installed/accomplished.

To the cleaning recommendation I would also add that you should do that cleaning with soap and water and the water has to be high pressure to get to the inside fins.  I know it is a mess  and maybe you should lift the unit off of its foundation but you could still hose it out without taking it off the roof.  The air that Dallas mentioned that doesn't get filtered has an oil content no matter how little cooking you have done.  Frying, especially.  Air may get it to work and if you do that get a magnum calibre shop vac and place it on the other side of the fins you are blowing.  Set up a strong fan in a nearby window and exhaust the air with the dust in it that gets past the shop vac.  You may even get this done without Mama getting all.....you know.

HTH

John