I'm trying to install a Honeywell Chronotherm IV Plus (T8624D2004) on a conventional residential system: gas warm air furnace & A/C (both single stage). The wiring is pretty standard: red - R/RC; white - W1; yellow - Y1; green - G and a common wire from the other side of the transformer - C; unused terminals - OT,OT,B,O,W2,Y2. My problem is that with the thermostat installed the outside A/C unit runs continuously (but oddly not the blower). My furnace guy reported that Y1 has 24V under all conditions (System: cool, heat, off, auto) and without regard to the temperature setting.

Is this a set-up issue? A stuck relay? A wiring error? Or what?

Do I have any recourse other than try a new thermostat?

Thanks for your advice, Tom

Not sure that y1 should have power all the time. Are you sure that the y2 termanal is not a y/y2?

y1 should not have power on it all the time. Are you sure you did the installer setup correctly?

standard
Terminal
Designations
Alternate
Terminal
Designations Typical Connection Function Terminal Type
B — Heat damper or changeover valve Output 24V powered contact
C Ba, C, X1, X2 Common Input
G F Fan relay Output 24V powered contact
O R Cool damper or changeover valve Output 24V powered contact
OT, OT — Outdoor temperature sensor (C7089B) Input —
R V 24V system or heating transformer Input —
RC — 24V cooling transformer Input —
W1 H1, R3 Stage 1 heating relay Output 24V powered contact
W2 H2, R4, W3, Y Stage 2 heating relay Output 24V powered contact
Y1 C1, M, Y Stage 1 compressor contactor Output 24V powered contact
Y2 C2, M, Y Stage 2 compressor

Www.kele.com/olcat/TC11/T8624D-V.PDF[/URL]

Sounds like you have way too much thermostat for what you are controlling. Try this first, put y to y2. See if this works. If not. I would suggest taking the thermostat back and getting a honeywell that is one stage heat, one stage cool, this will take the confusion out of wiring, and most likely cost you less money for purchase. Good luck and please let us know how things work out.