I replaced my Old Thermostat with a Honeywell CT87A 4447 about a year ago and only the Air conditioner/ cooling part works now. It worked perfectly well before, now the heat will not operate. There is only 4 wires R W G B, the unit is a Ruud Model #USNd-036J MFG
Date 1989. Is this unit a heat pump, I cannot find any information on it. If it is then this thermostat should not work on it correct. Or am I missing the boat , HomeDepot sold me this unit as a replacement and I believe it is for a heat unit only?

Eric Baker

Not sure by model # if you have a heat pump, but the wire indcates heat&cool only. Jumper R&W at stat to see if heat comes on. If it does your stat is faulty. Jumper R&W at furnace if heat comes on then you have a faulty wire from furnace to stat. If it were a heat pump, you should have an O terminal and wire

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Originally Posted by esquire1

Not sure by model # if you have a heat pump, but the wire indcates heat&cool only. Jumper R&W at stat to see if heat comes on. If it does your stat is faulty. Jumper R&W at furnace if heat comes on then you have a faulty wire from furnace to stat. If it were a heat pump, you should have an O terminal and wire

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Rheem/Ruud use B (blue) for there reversing valve.

I can't find that model number in there web site. You probably need to go into the installer setup and set it up for heat pump/2 stage heat? And if it has an O/B terminal you want the reversing valve energized on heat for Rheem/Ruud heat pumps. Also I'm pretty good with Rheem model numbers and that one doesn't ring a bell. Is it set up off the ground so it won't get buried in snow, if it snows there?