small cooling fan wiring

[Tikvah]

I have a mini-split and the condenser sits in the bay.  I've put louvers in my bay door for air and some holes with automotive cooling fans in the floor.  I plan to put a box over the unit to force its own fan to blow through the floor.  However, I want to use the cooling fans to kick in when the temperature gets too extreme.  Running both fans is overkill usually.  No fan is needed in moderate weather, and one fan when the temperature is hot.  So two fans might never be used.  But, I have them and want to wire them anyway.

http://www.amazon.com/All-Purpose-Temperature-Controller-Thermostat-Stc-1000/dp/B008KVGWT4/ref=pd_sim_hi_5?ie=UTF8&refRID=1F0GRP6578VEYRQCMCF3
I intend to use a controller like this so I can monitor the temperature as well as control the fans.  I plan to have two controllers.  One for low temperature, and one for high temperature.  Each controller should be two stage; to turn on as the temperature increases or decreases.  
What I see for a problem is when one fan is on it could back-feed power to the second relay.  

Am I going about this right?  Is there something simple I can do to prevent the back-feed?

Picture below of my bay...

[chessie4905]

   The fans mounted to the floor should have an air deflector lip sticking down a couple of inches on the front edge of holes  to avoid air movement turbulence going down the road.

[Tikvah]

The fans mounted to the floor should have an air deflector lip sticking down a couple of inches on the front edge of holes  to avoid air movement turbulence going down the road.

Yup, probably do that at some future date.  Right now I can't run it on the road because I have a Modified Wave Inverter.  Someday when I'm all grown up I'll get a Pure Sine Inverter and I'll put some kind of flap in front of the holes.

Thanks

[sledhead]

dave this is what I did
my extra fan is a inline 10 " 120 volt that turns on when the a/c turns on the cooling fan and I control the speed with a fan dimmer switch . the intake comes in through the old bus a/c compartment through a filter ,then through the a/c unit , then out through the 2nd fan and under the coach . It works really well on the road using my inverter or hooked up to the pole




<a href="http://s1280.photobucket.com/user/crane66/media/moto_0047_zps4089949a.jpg.html" target="_blank"><img src="http://i1280.photobucket.com/albums/a484/crane66/moto_0047_zps4089949a.jpg" border="0" alt="split unit a/c with power vent through floor photo moto_0047_zps4089949a.jpg"/></a>    

dave

[Timkar]

I intend to use a controller like this so I can monitor the temperature as well as control the fans.  I plan to have two controllers.  One for low temperature, and one for high temperature.  Each controller should be two stage; to turn on/off as the temperature increases or decreases.  
What I see for a problem is when one fan is on it could back-feed power to the second relay.  

Are you sure these controllers will work? For some reason it is looking for 12 VAC input and the internal relay is to control 220V AC at a max of 10A
Looks like what you want is something to control a 12VDC fan..

http://ecx.images-amazon.com/images/I/613ZgWugd2L._SL1000_.jpg

[Tikvah]

I haven't ordered the controller yet.  Yes, my fans are 12v DC

[Timkar]

Can't tell if this is the same controller that you are looking at as there are quite a few available if you go to home page of this link.
http://www.thermomart.com/digital-automatic-temperature-control-instruments?product_id=77

This one states will work on 12 VDC control power and the relay will handle up to 7A @ 12VDC. There are ones with higher current ratings for the contacts as well. (Don't know what your fans draw)
One of these for each fan set to your different temps and you are ready to go.
Other option is to wire thermistors in line with your DC power, but I am having trouble finding any and when I do they are about the same price as the "package units" in the link.

HTH...Tim

[luvrbus]

I don't understand this if one wants a thermostat control for a 12V fan why not just buy a adjustable thermostat for the fan sold by auto parts stores you can buy those for 20 bucks up you mount and run the probe to anywhere 2 wires and you are done with it JMO unless you just want another gadget to cause problems

[sledhead]

the biggest change for my unit with cooling was sealing the intake air from the exhaust air . after I did that my a/c unit ran a lot cooler and the temperature in the bay was a lot cooler as well .

dave 

[Tikvah]

I don't understand this if one wants a thermostat control for a 12V fan why not just buy a adjustable thermostat for the fan sold by auto parts stores you can buy those for 20 bucks up you mount and run the probe to anywhere 2 wires and you are done with it JMO unless you just want another gadget to cause problems

Every automotive temp sensor I know of is set someplace near 180 degrees.  Is there something else?
In addition, with the digital unit I can monitor temps from inside the coach.

I'm certainly open to ideas

[luvrbus]

The ones I use for transmission coolers fans go down to 32 degrees and I use a 3 dollar indicator light to tell when the fan or fans are off or on but you are dealing with AC you may want another system I just keep it as simple as possible JMW

[sledhead]

I use one like these to check the temps. in all my bays when driving or camping

http://www.ambientweather.com/amws15x3kit.html 

simple but effective

dave

[Larry B]

  Don't know if this is any help but to control my 12 volt dc fans on my hot water box heaters (be heated by a pro heat) I used 120 volt ac wall thermostats from Home Depot. About $20.00 . They are rated at 15amp AC and are contolling an 8amp DC load. Have been in use for 3-4 years and seem to be still working fine.  Just another thought you might want to consider.
        Larry B