Hippie

What do the four colored wires (green, yellow, white & red) control? I want to test a thermo in the next few days, and would rather know going in than figure it out as I go...

glennjanie

Hello Hippie:
If you haven't been schooled or experienced on thermostats, you need an HVAC tech to do it for you. One crucial thing about a thermostat is a place where you can just touch the wrong wires and burn the t-stat out. No repairs, no warranty, no sympathy; you just have to buy another one and try again.
If that doesn't scare you off, just take one wire at a time off the old one and put it on the new one and giver 'er the old smoke test. If you turn it on and it works without smoking you passed! Pat yourself on the back.
Glenn

Hippie

Yep, bad T-stat. I ended up working backwards, starting with jumping the controller on the heater, which engaged the heater, then removed the T-stat and connecting those wires (turns out it's heat only), then replaced the unit and all is good in the world.

Thanks on the assist.

glennjanie

I'm glad it worked out for you. The "one wire at a time" deal has saved me lots of heartaches. Congratulations on your smoke test!
Glenn

Hube

When a t stat is wired correctly by most(not all) hvac pros, the color codes are;
RED= power to T stat. Note; R & C are sometimes 'jumped'
WHITE= heat
GREEN= fan
YELLOW= cooling

Note ;unless a "diyer" knows exactly what is causing a T stat to not perform properly ,it is best left to a hvac pro.
in the majority of cases it turns out it is not the Tstat afterall.
In very rare cases does a T stat fail, it usually is another component in the heat/cool unit that breaks down.
Good luck.