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How can I modify wiring to solve a generator related problem?

I have two systems - a FHW oil fired heating system and a central A/C system on the thermostat. Instructions say common 24vac must come in from the A/C side, not the furnace side. This works fine under normal circumstances. But, I have a portable generator and a Gnerac panel wired for 10 circuits. The A/C system is not on the Generac panel; the furnace is. When I have a power outage and hook up my generator, my furnace had power, but my thermostat does not. Honeywell has been of no help on this, other than for one person to say that in no way can you take the 24vac common to the thermostat from the furnace. I have asked about several options, but cannot get them to reply. For example, put an A/B type switch off the therostate 24vac common with the ability to switch it to feed from either the A/C or the furnace. Can you comment and do you have any practical suggestions short of ditching this thermostat, which I really like otherwise?

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  • Heating & Co... Master
  • 1,095 Answers

A common is basically a ground. If you had to you could run your common to an electric outlet on the ground wire. Not recommended but I have done it and it will work. I'm a southern a/c guy with no oil furnace experience but if your furnace isn't sending 24 volts to the tstat it's not going to matter if it has a common because you will have lost your 24 volts when your a/c is off. If your furnace does send 24 volts to the tstat then I don't see why you could not get the common from the same spot, even if you run your common straight to ground. Good Luck

Posted on Mar 10, 2017

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Posted on Jan 02, 2017

Da Brain
  • 11 Answers

SOURCE: Wiring a Drayton Room Stat into central heating system

9 TIMES OUT OF 10 THE COLORS ARE THE SAME. MATCH THEM UP. FIRST LABEL THE WIRES ON THE ORIGINAL STAT, AND PUT THEM IN THE CORRESPONDING PLACE ON NEW ONE.

Posted on Oct 27, 2008

  • 24 Answers

SOURCE: Honeywell RTH 230B Thermostat Wiring

put the jumper back in RC and RH and that should do it.

Posted on Apr 15, 2009

  • 1 Answer

SOURCE: 44860 thermostat won't activate in heat mode

I had the same set and problem. I had a RC wire which is the power to the AC. But didn't have an RH wire which is the power for the heat. To fix this just use the jumper wire and insert it in with the RC wire and hook it up to the RH. Fixed my problem.

Posted on Oct 16, 2009

billyvangogh
  • 108 Answers

SOURCE: Replaced mercury thermostat w/Honeywell CT87K - doesn't work!

You need a specific thermostat for a Wall Furnace it is a Millivolt Thermostat and not a 24v standard thermostat....usually it will work anyway however if the powerpile (generator produces millivolts from the pilot light) is weak it may not be producing enough...or the Pilot light may be dirty and lazy...won't produce enough millivolts ...or you can have bad or dirty contacts or connections....or a combination of any of the above.....a 24v Thermostat and particularly a non-mercury thermostat has too much resistance in it for a millivolt system....as your Wall Furnace (other than the fan) runs on less than 1 volt

Posted on Oct 31, 2009

shastalaker7
  • 1515 Answers

SOURCE: Can't get new thermostat to work

When you have only 2 wires it is set up to run just a heater only. If this is a central heat/air unit, you would have 4, red for Hot, White for heat, green for fan, and yellow for cooling. sometimes they will have a blue wire that's not being used for a spare only.Some times you can use just the heat part of the stat if you connect the Red to r and if the subbas'e says Rc and Rh .If so, try connecting red to red and if it does say Rc and Rh that means red cooling and red heating.Run a jumper wire across the 2 reds along with the red from the wall. Connect white to w.Try programming the heat and see if it fires up. If not, you will have to replace stat with a 2 wire Heating only thermostat. Do not pull any wires up from the transformer as you will burn it out!! Just remember, 2 wires are for a heater only!4 are for heat and cool, and 8 are used for a heat pump.Sometimes the new stats have the red jumper wire in place and all you have to do is hook your red to either end of the jumper, and then white to W. If no RCand RH, get a heat only stat, or it will never work believe me, I know this.Good Luck and let me know if you need more help. Shastalaker7

Posted on Nov 07, 2009

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