I'm replacing a Honeywell T8575D2003 with a Honeywell RTH8500. Didn't think there would be issues, manuals are all straight forward. However when I removed the T8575, the wiring set up did not match what the RTH8500 was expecting.

The T8575 has 8 wires connected as follows

< 1 50/60hz White
24v < 2 Com Green
3 Heat Yellow
4 Cool Orange
5 Sw/Op
< 6 Com Brown
Fan < 7 Low Red
< 8 Med Blue
< 9 High Black
10
11

How does these wires match up to the contacts on the RTH8500? The RTH8500 uses the NEMA thermostat wiring guidelines TStatWiring (http://www.hvacmechanic.com/tstatwiring.htm)

Any help would be appreciated. Thanks

In many cases the original installers did not follow the standard wiring code. You might end up tracing all the wires back to where they go on the unit,see what color does what, and wiring accordingly.

This could save you from having short circuits and damage to the syatem or new thermostat.


The old one is a fan coil stat.

http://customer.honeywell.com/techlit/pdf/95c-00000s/95c-10897.pdf

The new one is not but could probably made to work.

http://customer.honeywell.com/techlit/pdf/PackedLit/69-1902EF.pdf