Carrier type furnace with mercury thermostat won't heat normally except when the weather is warm, it randomly will start after fan has been switched to auto. Will cycle on and off once or twice, then stops. Quick fix?

call a furnace repair service locally

possible stat failure

carrier infinity 96 furnace went to turn down the thermostat and their was no power to it and the furnace doesnt run

The stat that works is called the main and the other two are called slave stats. The stats must be set to heat or cool the same as the main. If you want one room to cool and one to heat , sorry. Need to upgrade to auto changeover. Is this AC actally a Heat pump?

Two wire hookup on the old thermostat tells me that it was set up for heating only. You will most likely need a modern thermostat. But in the meantime try this with the old one. The two red wires on the furnace are probably Rh & Rc. If so these can be put "together" on the R terminal on the old stat. The two W's on the new furnace are probably W1 &v W2 This is for first and second stage heat. You can put the two "together" on the W terminal on the old stat. Do not hook up the greens (blower fan wires). Do not hook up the blue wires (They would go to the Y terminal on a modern stat for airconditioning.
Who ever sold you the furnace should have offered you a new thermostat.
Good luck....

The digital thermostat must be programmed for GAS heat.
If the problem occured before the t-stat change and is still happening, the problem would be with ignition within the furnace.

Could be a defective thermostat in the plenum.
When a gas furnace shuts down the fan(blower) will run until the plenum cools to the safe range. Usually 1 and 1/2 minutes.
Intermittent operation is a defective thermostat or relay.

Code 12 I believe is power up after power off and a call for heat from the the thermostat. If you have a weak door switch that may be vibrating and going on and off it would cause this as would any thing that causes the power to drop low or out then reapply its self. try holding the door switch in while watching the board and after 2 or 3 minutes the furnace should go on to lite and the blower cycle off. If it stays in this mode try turning the thermostat off (heat - OFF -cool) and then push in the door switch nothing should happen except the lite on the board come on and stay on. If it does this than have someone turn the thermostat to heat and see if it starts or put the door on and set the heat and see if *** goes through the normal cycle of heating. If however it goes right back into the blower mode and shows the 12 code your problem is still with you. So next remove the wire on the "W" terminal on the board. Retry power to the door switch and now nothing should be on except the red lite. If it tries to start the 12 code and blower up again Im pretty sure you have a bad ignition/blower control board.

You have a carrier or bryant AC Coil model number and the sn says 1995 and its 5 tons and if you actually have a heat pump with the gas furnace you have what we call in the business a dual fule heatpump setup. There are a number of items that could be causing your problem. I would recomend that you first look for the relay box discribed below and if you have that put the wires at your furnace (R &W) together with nothing else on them. If it lites then the problem could be anywhere, thermostat, wiring, the control box which has about 4 to 6 relays. If it dosn't lite the furnace is where your problem is or at least one of your problems is and start there. remove anyother wires on R&W before reapplying power. Also if you have the control box below it will have its own 24v control transformer but your going around that with the test I mentiond here. Oh yes and if it hasnt been modified you'll have to keep the solid door on it to apply power to the furnace.

There are a multitude of items it could be but I believe your age furnace has an auxiliary sensor - relay assembly it is a box about 18 inches long X 6 inches square. has about 10 terminals on it. And it will look like a birds nest with all the wires going and comming out. Id have to suggest you call someone and here's what Id do if I were you. If they say they aren't sure but think its in the relay assembly for the dual fuel control ask them to call carrier or Bryant and request they talk to a service trained expert there or recomend someone. You can do this instead of paying for 2 people. Just ask them if they know about Bryant or Carrier Heatpump dual fuel setup before you tell them to come out.

The newer dual fuel thermostats around $300 - $400 plus an out door sensor about $30 will get you fixed for parts. NO more relay box needed just the out door sensor and the compatable thermostat. if this is where the problem leads. The thermostat cost will depend on if you want the program feature. If someone is home all day Id suggest you probably don't need this feature.

This should get you headed in the right direction. If it helps you please grasde me accordingly, and GOOD LUCK!