Thermostat Wiring Help

mmqbMarch 21, 2010

Here's my issue: I have a little tiny greenhouse (more of a box than a house) that I am raising vegetable seedlings in until the night temps are warm enough to transplant into the garden. During the day the temps are starting to get hot to the point that I need to install an exhaust fan.

I have an old 12V PC fan and a 12V wall adapter power supply that I'd like to connect together with a thermostat. I have an old Honeywell manual dial thermostat that should work, but I need some wiring help. The thermostat has the following wiring connections: G, RC, RH, Y, A, O, W, and B. I only have two wires coming from the power adapter (hot and return), so where do I hook them to on the 'stat to make the fan work? Remember that the honeywell is not digital, and should work with this application.

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Try RC and Y.

Here is a link that might be useful: Thermostat signals and color code

    Bookmark   March 21, 2010 at 9:27AM
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Do you mean to wire it this way:

Power supply --- hot to RC on Thermostat
--- Return to Return on Fan

Thermostat-- Y to hot wire of Fan

If this is incorrect can you just tell me the correct wiring configurations? I am pretty new to this. Thanks again.

    Bookmark   March 22, 2010 at 2:48PM
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Yes, you'd just connect the R (or Rc) and Y terminals in series with the fan.

Make sure that the thermostat's contacts have enough current capacity to handle the fan's load. They probably do. If not, though, you'd need to add a small relay to preserve the thermostat.

    Bookmark   March 22, 2010 at 8:36PM
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I have tried done the following and it is not working:
Power supply to RC
Power return to fan return
Thermostat Y to fan supply

I tried this and it worked continuously without the thermostat controlling temperature as a switch:
Power supply to RC
RC jumpered to Y
Power supply return to fan return
Y to fan supply

Is is likely that the thermostat is bad, or do I do I have incorrect connections? Sorry to be so electrically challenged.

    Bookmark   March 23, 2010 at 11:10AM
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That should work....either a bad t-stat or not on the cool setting

    Bookmark   March 23, 2010 at 7:23PM
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