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AJD63 02-18-2011 08:51 PM

RTH7500D t-stat to heat pump wiring - need help
bought honeywell RTH7500D digital programmable thermostat from Amazon which is supposed to be compatible with heat pump system with auxilliary heat to replace coleman 3600-367 thermostat. furnace for mobile home is nordyne model FEH-012HA-04 [41000 BTUH].
old t-stat had terminals O,B,G,E,Y, R,X,L AND W2 with a wire on each terminal EXCEPT the E terminal. [8 wires total]
labeled and disconnected wires and then wired new t-stat per manual as follows; B wire to C terminal, G wire to G, Y wire to Y, O wire to O/B, R wire to R terminal which is jumpered to RC terminal, W2 wire to AUX, X wire to E and finally L wire to L.
installed t-stat and programmed functions 0170 to 7, 0190 to 0, 0270 to 9, 0300 to 0, and 0530 to 1
turned circuit breaker back on and nothing worked. called honeywell tech support and they reviewed my wiring and programming, said it was correct and that I had a bad t-stat. contacted Amazon and asked for a new t-stat to replace this defective new one. installed new replacement with same result - nothing works.
did continuity checks from t-stat to furnace junction box and noticed the old [X] black wire goes to transformer common. figured this wire should be going to C common on new t-stat, so moved it there.
so now what do I do with B brown wire ? already have O orange wire at O/B terminal. manual says ' if old t-stat had separate O and B wires, attach the B wire to C terminal. if another wire is attached to C terminal [my case] , stop and contact qualified contractor for help ................why I'm here.

hvactech126 02-18-2011 09:03 PM

this thermostat will not work with your system, you need one with separate o and b terminals. You have a rare system that requires this setup.

AJD63 02-18-2011 09:12 PM

thanks for the reply. wish honeywell would have told me this.
any recommendations on t-stat with separate O + B terminals for heat pump with aux heat ?

hvactech126 02-18-2011 09:25 PM

white rodgers 1F95-1277

White rodgers stats typically have separate o and b terminals

AJD63 02-18-2011 09:41 PM

thanks again. looked at specs and first seems best. second one actually has combined O/B terminal.
help appreciated

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