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Author Topic: Roof Top A/C question  (Read 1835 times)
txjeff
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« on: June 09, 2010, 05:48:28 AM »

Has anyone wired their rooftop a/c so the fan  doesnt run all the time. I have the 15000 Coleman March units. I have a wabasto heating unit that is wired into a house type thermostat and was looking at connecting the rooftops to the same thermostat. I know the thermostats are 12v dc controlled and the rooftops are 120v a/c controlled. Any thoughts HuhHuhHuh?

jeff
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73 MC-7combo
Brenham, Texas
Jerry32
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« Reply #1 on: June 09, 2010, 06:00:21 AM »

Yes that is hat I did althought not a 12 v thermostat. I ran my ACthrougha 120 v thermostat so that it would completely shut down when temp was reached as I hate to have that fan blowing all the time. Jerry
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luvrbus
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« Reply #2 on: June 09, 2010, 06:06:47 AM »

Another idea is to have somebody send you a wiring diagram on a Carrier with the remote supposed to be easy to do as they have 12V controls



good luck
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Dreamscape
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« Reply #3 on: June 09, 2010, 07:33:33 AM »

This thread is very timely for me. My wife complains of the fan noise all the time! Except at night when it helps to drown out my snoring! Roll Eyes

I'll look for the Carrier diagram when I have time.

I'll be watching this one.

Paul
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txjeff
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« Reply #4 on: June 09, 2010, 08:02:40 AM »

Jerry

Did you wire around the fan control and the thermostat on the a/c unit?

jeff
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73 MC-7combo
Brenham, Texas
James77MCI8
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« Reply #5 on: June 09, 2010, 08:21:24 AM »

Duo- Therm thermostats have the option for the fan to be "on"( the fan runs continuosly, regardless of the temp.) and auto(the fan shuts off when the thermostat is satisfied.)
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Sean
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« Reply #6 on: June 09, 2010, 09:17:00 AM »

We use standard household thermostats (the electronic style -- don't use ones with mercury switches) that have both heating and cooling settings, and these control relays which energize the roof air circuits.  The thermostats have built-in five-minute cut-out delays so that the T-stat will not try to restart an AC until five minutes after it has been stopped.

We use 24vdc for control voltage and relays with 30-amp, 120vac rated contacts.

More complex then you need, but here is our circuit:
http://odyssey.smugmug.com/Architecture/Drawings/63883_XJHit#2228266_dqfSH-O-LB

The part at the bottom with the yellow wire is the roof air circuit.  You can see that we control three roof airs with only two thermostats, by diode steering.  The middle air comes on if either the front or rear T-stat calls for cooling.

We just leave the built-in 'stats on the units on the highest setting.

-Sean
http://OurOdyssey.BlogSpot.com

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TomC
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« Reply #7 on: June 09, 2010, 09:21:54 AM »

Even thought the fan maybe noisy, when the A/C is needed, it has been proven that the electrical draw is much lower WITH the fan running continuously.  It eliminates hot spots that when the A/C kicks back on has to overcome to bring the temp back down again.
I had a friend in Cinnci, Oh that I simply had her change the house A/C to continuous fan run when it was hot and her electrical bill came down nearly $70.00!  
I understand the noisiness of the roof top A/C, that's one of the contributing factors why I'm installing my Penguins in the basement of the truck (also since there isn't enough height room left on the roof).  At night it would be nice to have the fan kick on with the compressor only.  You could wire an either or switch in and have a relay that would activate the fan motor when the compressor came on.  Good Luck, TomC
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txjeff
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« Reply #8 on: June 09, 2010, 09:46:50 AM »

Sean,

Your design is kinda what I had in mind with the relays. It looks like your fan shuts off when the compressor shuts off. I was looking at using the fan delay on the tstat so the fan run a few minutes longer (not sure if that makes any difference)but it would require two more relays. I was curious to why use the electronic tstat instead of the mercury switch ones?
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Brenham, Texas
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« Reply #9 on: June 09, 2010, 10:11:52 AM »

I was curious to why use the electronic tstat instead of the mercury switch ones?

Jeff

The mercury ones need to be level to work correctly and the forces put upon it from stopping and starting while driving would cause all sorts of intermittent and stop/start contact action.

Cliff
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« Reply #10 on: June 09, 2010, 10:52:57 AM »

I really dislike how much noise rooftops make and wanted to do away with it at least while the compressor was off.  I put an a line voltage thermostat in the circuit to do it.  It worked, however it seriously affected the cooling by noticeably increasing the time the unit took to react to changing temps.  This made the temp fluctuation much larger.  As much as I liked the concept, I did not use it much.  Maybe it would have worked better if I had put the thermostat close to the ceiling.
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