RV rooftop unit fan modification

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  #1  
Old 05-18-07, 12:34 PM
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Question RV rooftop unit fan modification

Anyone Have Any Thoughts On How To Modify An Rv Rooftop Unit So As To Have A Stat Shut The Fan Off And On, So That It Does Not Run Continuously As Do Most Of The Residential Wall Or Window Units Out There Do.
Thanks
 
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  #2  
Old 05-18-07, 06:15 PM
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Honestly, no

Do you mean that when you start the engine the fan is running? no control at all?

I cleaned the condenser coil on my Dad's unit a couple years ago and he didn't mention this as a problem, and I didn't look too much into the system.

I'd be interested to learn.

What mobile do you have?

Any model, serial numbers off the unit? Tsats make model?

I'll try to almost anything once.

Chris
 
  #3  
Old 05-18-07, 09:19 PM
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Wink

Like said it helps a lot to know just what you have there. So that we can try and help. The main thing is what power does it work off of? You might take the cover off and find a wire schematic to see what controls it.

Might also check out this www for a tstat.

http://www.pplmotorhomes.com/parts/rv-air-conditioner-parts-1.htm?source=google
 
  #4  
Old 05-19-07, 06:33 AM
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RV Rooftop

Its a standard Coleman 7000bTU unit, they are all low profile units with a thermostat built into the unit case. Satndard operation for these units is: The fan comes on when the unit ids turned on and the compressor cycles until that sta is satisfied, however they are built such that the fan continues to run continuously.
I spoke with tech support @ www.rvcomfort.com/rvp/rvp.php, the manufacturers for Coleman and probably others and was informed that the OEM's want this design and so that is how they make them( at least up until my model year of 1999)
If I understood him correctly the stat is wired directly to the fan .. he said that he had reports of some guys wiring the compressor directly to an external stat and of course toasted it.
I'm not in the a/c business but have a working knowledge of it along with some pretty extensive electrical experience. I can't believe that there isn't a way to cycle this fan along with the compressor. Thanks for your input
 
  #5  
Old 05-19-07, 06:44 AM
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"pretty extensive electrical experience."

Then why haven't you located the wiring diagram to help us give you more of a clue as to what and where to look?

Chris
 
  #6  
Old 05-19-07, 07:22 AM
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rvcomfort.com

has many pages of wiring diagrams. What is the full model number?

Chris
 
  #7  
Old 05-19-07, 07:43 AM
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wiring diagram

Jarredsdad
I pulled the shroud and took a picture of the wiring diagram, any idea how I can post it?
 
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Old 05-19-07, 08:02 AM
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email

check your private messages
 
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Old 05-19-07, 09:46 AM
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Simple enough

Caution though, starting the compressor and the fan at the same time may trip your breaker!

Why they seem to be breaking neutral beats me.

Looking at the wiring diagram we're using the top left and lower right.
The lower right has th t-stat. White comes in on the right, yellow come out and to the compressor through terminal #1.

Back on the right side of the stat, white also comes off and goes to the fan through terminal #9, that's why the fan runs in hi or lo cool independent of the compressor.

Now to the top left (upper unit wiring) if you move the white from terminal #9 to terminal #1 the fan eill only run when the compressor is on. And you have to do it up here. If you do it in the ceiling assembly you will bypass the stst and BOTH will run all the time.

If this is a plug type deal and you have to cut wires and wirenut back together don't cut the wire too short near the plug incase you need to go back to original config.

Because both motors starting at the same time may trip the breaker, maybe hard on both motors and capacitors.

Look again at the upper right diagram. See the "START CAP"? That's there to give the compressor a big kick in the butt to get it going, meaning a lot of amp draw on start up.

You only have 20 amps to work with, top right of the picture.

BE SAFE, Double check yourself a couple times before you cut.

While redundancy can seem redundant, I don't think it ever killed anyone.

Chris
 
  #10  
Old 05-19-07, 10:31 AM
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Hard on both motors

Chris,
Understood.
Would it make sense for me to open it up and get the ratings of the start capacitor, compressor and fan motor before modifying this?
I can't afford to fry this unit
Appreciate your help
john
 
  #11  
Old 05-19-07, 12:18 PM
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Can't hurt.

But I don't think you will fry it. It was built this way for a reason. What that is is anyones guess. Could be as simple as although you use electricity the system in your house will be more efficient if you run the fan all the time. Meaning constant air flow eqaulizes the temperature throughout.

Could also be because of the initial inrush of amperage starting both at the same time. Do you have an amp meter? That will allow you to check the max amp draw on start up. If not, the thing to do is try it once. Like I said leave yourself enough wire to reverse your mod.

Without an amp meter start the system before the mod. Listen to how things sound starting. Then do the mod and listen again. Are things slower? Does it pop the breaker right off? If so go back to normal.

See, the problem we have at DIY (at least I do) is we are not where you are and we don't have a clue as to your abilities so for saftey sake I have to get a "feel" for you before I start explaining how you can get into an electrical mod or repair.

If I were doing what you are, I would take amperage readings on both the comp and fan as each starts. My meter will hold the max reading so I could get the max from both motors on start up add together and have a total. If it's more than the 20 amp breaker you have too long, the breaker will trip.

So, all that said, go ahead and try it. There are 3 possable out comes. 1) everything is fine. 2) it works but the amp draw is large and (assuming generator power) the unit starts slow and the generator gets loader to overcome. 3) the amp draw is too great and the breaker pops.

You may also be able to add a delay on make timer to allow the fan to start first and the compressor 5 to 10 seconds later after the fan is up to speed.

But at this point just do it. One try will not kill the unit.

Chris
 
  #12  
Old 05-19-07, 01:29 PM
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one try

Sounds like a plan, my ampmeter stayed in NJ when I moved south to fl along with most everything else. I follow everything that you are saying, maybe the autozone has one in their lend a tool program .. if not I'll do a quick cut and splice and see what happens.
thanks,
Be talking at ya again
john
 
  #13  
Old 05-19-07, 04:11 PM
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I always find it helps to just draw the wire lay out on paper first. look at it then do it.
 
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