Viewstat on old HVAC installation

Yannick · November 2006

Hi,

i'm installing a Viewstat on an old HVAC installation. Well, precisely an old pump inline with a LPG furnace. This pump only have 2 wires that serve as the switch for the ON/OFF. Today thoses wires are hook-up to an Honeywell mecanical thermostat. Of course the voltage on this line is 240VAC.

Till now, i've manage to find a set of Ficher Relay 24VAC (Coil) and 240VAC 10A on each tips (enough for the pump to work). I'm struggling to find out on which mode should I setup the Viewstat and on wich pair of terminal should I wire this relay?!?

Thanks in advance for you help!

Yannick

DHawthorne · November 2006

As I understand it, the modes only affect the dwell timing from when it goes from off to on, and vica versa. So you need to find out what the spec is on that furnace, and see what is closest. I think this is more important for oil furnaces than gas; I would imagine your LPG furnace has built in safeguards against going on/off too quickly, and it's more a matter of what will provide the most even heating. I would call the HVAC guy in on it to be absolutely certain.

As for wiring, connect your relay triggers between RH and W1 for the furnace. I assume it handles the fan on it's own, but if not the fan trigger goes to G.

Yannick · November 2006

Thanks DHawthorne.

I've got a chat with the furnace guy. The furnace have protection against rapid off/on trigger, so as the pump. The relay trigger has been wired between W1 and the COM of the external 24VAC power supply. It just works perfectly... now the hardest part is to come, tuning the system to take in account it's inertia. But that's another problem.

thanks again

Viewstat on old HVAC installation

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