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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Trying to change a Honeywell pc8900 t-stat over to a nest

Customer Question

trying to change a Honeywell pc8900 t-stat over to a nest
Submitted: 2 years ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 years ago.
Hi I'm Brian and I'm here to help! Is your Honeywell PC8900 thermostat part of a Honeywell Perfect Climate Control system? Is there a remote panel that the thermostat connects to (normally installed near your furnace or air handling unit)? Also, can I get the model numbers of your Carrier system please? Some 16 SEER systems are two speed/variable speed and that can have an affect on wiring. Thanks,Brian
Customer: replied 2 years ago.
model #24acc648a300 We have gas heat. furnace was not chaged just a new AC and coil.
Expert:  Brian HVAC Guy replied 2 years ago.
Thanks for the additional info. Everything I can find on the Honeywell PC8900 thermostat relates it to the "thermostat" (a misnomer) of a two piece system with a control interface (thermostat) and a remotely installed control panel. The 'thermostat' is connected to the control panel with four wires and is a communicating type of thermostat with no local relay control. The NEST thermostat is a local control thermostat. Meaning the relays to start/stop your heating, cooling and blower are within the thermostat itself. The Nest will require a minimum of five thermostat wires to achieve direct control over your system. With all that said, can you tell me how many conductors there are in your thermostat cable at the thermostat location please? Also, to install the Nest in place of the Honeywell, it will require some wiring work at the Honeywell control panel location. If you have five or more wires between the thermostat and control panel location and between the control panel and your furnace, this could be just a matter of connecting some wires together with wire nuts at the control panel location and abandoning the control panel in place. Pictures are worth a thousand typed words! Pictures of the control panel wiring would make this transition much easier to explain how to perform. You can upload pictures here by using either the paper clip icon in the text formatting toolbar or the Attach Files button at the bottom left. Both buttons are located in the reply dialog box where you type replies to me. Thanks,Brian

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