Question about new t-stat and jumpered wires


Old 08-22-13, 09:02 AM
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Question about new t-stat and jumpered wires

I have a heatpump system, two stage compressor, variable speed furnace and an arzel zoning system. The old t-stat is a Robertshaw 9620. The one I want to try to install is a Nest. Here are the wires I have:



I don't have the colors of them handy, but these are the ones hooked up to the terminals in teh robertshaw. The problem is that I have an additional jumper between E and W2. Why? Nest says NOT to jumper it on the Nest as its all internal, but im curious why mine is jumpered.

Also, why do I only have an O and not and O AND B?
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Old 08-23-13, 08:55 PM
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Your old stat requires the jumper between Aux and E because it is not internally jumpered.

O energizes the reversing valve of a heat pump for cooling and B is to reversing it for heat.

Rheem, Ruud and weatherking use B and almost every other brand uses O.
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