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T Stat wiring issue

I am currently working on a 2 heat 1 cool system that has a single speed air handler. What I am trying to accomplish is to have the zone of baseboard on W1 or first stage heat, and the air handler on second stage heat. The issue is that the tstat energizes R-G and turns the blower on whenever there is a call for heat. So now I think, why not install an aquastat set to 140, that will hold off the blower until the second stage zone valve opens. This would hold the blower off until the second stage calls on.  BUT, now how do I deal with turning on the fan during the cooling season ? There is only on Red wire with a jumper between RC and RH. Is there a way that I could wire in a RIB relay or something to bypass the aqaustat ? 


  • MarkPFalade
    MarkPFalade Member Posts: 68
    edited November 2009
    The Tstat,,,

    Doesn't it have an internal switch that will allow you to turn off the part where it energizes blower for heat? If not, get a t'stat that does. Generally a tstat will only energize blower on a call for heat if it is designed for electric heat. These days most make either option available through the switch I mentioned, so if the one you have doesn't you need to get one that does. You'll still need an aquastat to energize blower for heat. Besides that I'd almost suggest reversing your plan and make blower first stage and baseboard second stage as I believe the hydro will be more efficient. But I don't know exactly what you're up to with the system so I can't make the call for you.

    Good luck!
  • dynamic
    dynamic Member Posts: 20
    gas/electric switch

    I had to put it on electric to energize the blower on heat. If not the blower would not come on at all. I currently have it set up that way, but the customer wants it the baseboard first and blower second. He has a continuous loop on the boiler and it costs him less by not using the blower, until he has to. The boiler is already heating for other parts of the building. Plus, now I am determined to see this work now......
  • MarkPFalade
    MarkPFalade Member Posts: 68
    edited November 2009
    In that case,

    Put your aquastat on to run the blower for heat and switch your tstat back to gas. Unless I'm missing something.

    OK, I reread, here's what you do. IF your fan relay is double throw (NO contact / NC contact) wire the NC contact to the aqua stat and then to the motor lead directly. When "G" is "off" the aquastat is in control through the NC contact. When G is energized it will open the aquastat circuit and feed the motor through the NO contact. If your fan relay is NOT double throw you need to change it to one that is. You CANNOT wire the aquastat on the 24V side to energize "G" when it closes because "G" will then backfeed "Y" and call in the cool simultaneously with the heat. Never a good thing. If you have a 3 speed motor you can hook high to the fan relay NO contact and low through the NC contact/aquastat which will lower amp draw while using the fan for heat.

    You could also use a time delay relay. Put the 24V side in parallel with the W circuit and use the relay to power the blower motor directly. It would probably be a less expensive way to go than buying an aquastat. If you are using only one speed for both heat and cool your job is done. The TDR and fan relay are in parallel and either will run the blower. If you want to use two different speeds then you would have to wire the high voltage side of the TDR through the NC contact on the fan relay as described above for the aquastat. The object being you don't want it to inadvertanly energize the high AND low speed motor leads at the same time. That would let the magic smoke out of the motor and it needs that smoke in there to work. So the double throw relay isolates the motor leads from each other and prevents this. Let me know if this solves your problem. I did my best to explain this but if it's not clear to you, ask questions. ;-)

    Note: if you are going to run one speed for both heat and cool the isolation is not needed, you simply wire the aquastat / TDR contacts in parallel with the fan relay NO contact. If you would like to use two speeds THEN the NO / NC contacts need to come into play.

    I once looked at a large 20 year old commercial system that "hasn't worked right since they put it in" there had been numerous people looking at it over the years. By some stroke of luck I noticed the fire coming on during a call for cool. Yup, W and G had been wired together to run the blower for heat during install and every time the cool called the heat came on with it and every time the heat called the cool came on with it. 20 years!
  • geno54
    geno54 Member Posts: 43
    edited December 2009
    HydroAir Wiring

    Here is a method for wiring you could use. This works on conventional systems but not on VS. It uses a L6006C strap on aquastat (3 terminal - R W B). It isolates the G terminal so as not to "backfeed"  to the Y terminal. Been using this method for years. This is for Single transformer system, dual transformer would be slightly different 
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