I’m hoping to install a programmable thermostat in place of two thermostats (1 heating, 1 cooling) in my house (built 1999). Seems simple enough; get a new stat with an R and an Rc to take care of the separate power supplies, and wire everything else the same. However, I’m puzzled as to the way the cooling is wired, so I’m not sure I can go ahead. Maybe someone can explain what I’ve got?
First, the stats are separate (next to each other). The heat is a simple 2-wire setup. No problem there.
The cooling thermostat is using 5 terminals (Y, O, R, G, B). Honeywell (and my wiring diagram) confirm that the B terminal is used for heating, not cooling. It should only be energized when the stat is in the HEAT position. I don’t see anything jumpered. What gives?
One other piece of information. The cooling has two zones controlled with dampers. The other zone is slaved off of this thermostat (in other words, this stat has to be set to COOL or the other zone won’t run the A/C no matter what).
Thanks for any suggestions,
Pete
Replies
Try here instead.. http://www.hvacmechanic.com
Thanks
Rav
Well, I got it sorted out after I downloaded manuals and wiring diagrams for my thermostats and the A/C controller. Turns out that whoever did the original wiring connected a wire that wasn't actually doing anything, but it was confusing. Here are a few key lessons learned for anyone who finds this post in a "Search":
Different thermostat/controller/equipment manufacturers use different definitions for the lettered terminals.
There's a lot of well meaning but inaccurate advice available on the internet.
There's no substitute for wiring diagrams and manuals from the manufacturer of your thermostat and equipment. The manufacturers' web sites are a great source of information. Start by finding the model numbers on your thermostat, and on whatever it is wired to.
Honeywell has a great web site. Not all their manuals are accessible from their "homeowner" site, but they are on the web and you can find them by poking around from the main site.
If you have a Honeywell round thermostat (T87x), the real business end is the base (after you unscrew the front part). The bases have their own part numbers and there are different flavors for different situations.
Pete