Question about Honeywell Programmable Thermostat Heater

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Changing Thermostats I have an American Standard furnace with Heat Pump. The present thermostat is a ASYSTAT655 (American Standard). I want to replace with a Honeywell RTH7400 But the wiring is confusing. I went through Honeywells "Wizard" but the only options were for systems with 7 wires Mine has 8. I don't want to blow something up it is cold and gonna get colder

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Re: Changing Thermostats

This is one where you will need a good control man or woman. The American Standard ASYST system is not intended for the homeowner to change out. It has a room sensor wire that others do not account for.

Posted on Jan 16, 2008

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You should have more wires than just two, and you should also only have 1 power wire at the thermostat. Red is usually the power, white is usually for heat, unless it's the wires going to the outside unit. On a normal system, those two wires are the power and common going to the contactor. Heat pumps have more. However, you will not actually need a common terminal, all commons are just grounded to the units housing, therefore your common is nothing more than a ground wire. Hope this helps!

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My themorsat stop working,and I replaced the batteries.

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Furnace Produces No Heat Possible Causes

Possible Repairs
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  • To adjust the heat anticipator, please see Heat Anticipator Adjustment.

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1 Answer

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Blue is usually a common/ground in standard 5 wire applications. Older installations have 4 wires where the blue was used for cooling. It really depends on what you have and what you need. Thermostats only need the common wire when there are no batteries and it uses the furnace to power the thermostat. This is the normal wiring for most systems:

Red(R)- Power/24v
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That is for common conventional systems. Heat pump systems and some high efficiency systems have more than 5 wires. Other wires you may have:

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1 Answer

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Have it programmed correctly.

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