ajburnet Posted July 7, 2012 Share Posted July 7, 2012 Hi all,I've just installed my C4 thermostat which works, albeit not with power stealing I think. With power stealing enabled it starts up my furnace and ac (presumably as R/RC are the 24v + for both). Anyway - it operates everything fine on battery but obviously not a long term solution.Are there any tips or things I should try other than having a common (assuming my Lennox furnace has one) to the thermostat?Thanks!Alex. Link to comment Share on other sites More sharing options...
jmb Posted July 7, 2012 Share Posted July 7, 2012 Never got mine to work without the common. Once I ran the common, I've been good for two years. Link to comment Share on other sites More sharing options...
ajburnet Posted July 8, 2012 Author Share Posted July 8, 2012 Thanks - will try the included bypass resistor but guessing I'll probably need the common...Thanks! Link to comment Share on other sites More sharing options...
ajburnet Posted July 8, 2012 Author Share Posted July 8, 2012 Thanks. The bypass resistor didn't work so I ran a new common wire but this doesn't appear to be powering the tstat.My furnace actually has two connectors, both with the usual RBWY etc.. One has a 'c' which I've run this wire to however the stat wires all run to an interface board which doesn't have a 'c' terminal but does have two terminals named 'output' which are connected with blue wires to the transformer. I'm suspecting these may be common terminals for tstats - the other set of terminals seems to have the condenser terminating there.Will check out the 'output' terminals with a multimeter and see what i can find out as I suspect they are 24v + terminals which I don't want to connect to the TSC terminal on the stat I think! Any thoughts appreciated!Thanks,Alex. Link to comment Share on other sites More sharing options...
ajburnet Posted July 20, 2012 Author Share Posted July 20, 2012 Well - I ran a common and all was well in the world for a few weeks. Unfortunately one of the control boards on the furnace died. It may be a coincidence but it's possible the C4 thermostat had a part to play.Any opinions? I'd love to have it back in but I'll need to get an idea of whether it was a likely cause of the failure!Alex. Link to comment Share on other sites More sharing options...
ajburnet Posted July 21, 2012 Author Share Posted July 21, 2012 Opinion so far is this is most likely a coincidence given it had no problems for over a week.Nonetheless, I'm contemplating using a separate 24vac transformer to power the stat just to be extra sure. Has anyone used this config?Thanks,Alex. Link to comment Share on other sites More sharing options...
LSDave Posted July 21, 2012 Share Posted July 21, 2012 The furnace logic board should have a 3-5 amp fuse on it. Which should pop if there was a short circuit situation. Do you have a digital volt meter to test with? I ended up getting the common right from the transformer in the furnace. I've seen a "c" on a logic board that was a neutral for a 120v humidifier. Just check your voltages before you hook up and you should be good. Link to comment Share on other sites More sharing options...
ajburnet Posted July 22, 2012 Author Share Posted July 22, 2012 The fuse didn't blow and I did check the voltage - it showed 14vac..As I say - probably a coincidence but am going to try using a separate transformer just to play it safe!Only other thing is I had the tstat set to control the fan which I suspect should be controlled by the furnace so I'll try with the setting for that.Thanks,Alex Link to comment Share on other sites More sharing options...
CFUG Posted July 22, 2012 Share Posted July 22, 2012 14VAC where? The supply V for all relays and the C4 stat should be 24VAC... Link to comment Share on other sites More sharing options...
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