Log in to Reply. If we have a 30°C temperature sets in our air conditioner display and, our room’s temperature is below 30°C, then our outer unit will not be operational. Is this a problem with the unit, or the thermostat inside the house? I have tried a great many wiring combo's but none seem to work well. We currently have the system shut off at the breaker to prevent it from running. I have a Rheem unit with a furnace that has a Honeywell St9101 control board. There were four or five wires together in a cable at the thermostat, do any of them go to my outside ac unit, or just to the furnace? I cant seem to see any old red and white wires in there at all. Always set the temperature of your air conditioner below from the temperature of the room. Red wires, specifically Rc wires, are responsible for 24-hour volt AC power from your transformer. 100 ft. 18/2 Solid Thermostat Wire, Brown (17) Model# 210-1002CR $ 17 38. it is maximum probably the thermostat is soliciting for A/C indicating the the two wires in question are energized at 24 volts ac. AC. Check HVAC Control Unit Fuse. That thermostat wire amp capacity I cited was for copper wire, soft-annealed, nick-free. I installed the thermostat originally with the PEK (eveything worked minus the outside unit running, by the way we have a furnace) because I didn't think I had a C wire, but after pulling some of the wires behind the thermostat I think I have one (it's blue). It's not even trying to … 2. Rc wires connect to the RC terminals on your thermostat. If there is no power to the thermostat then you will need to call a professional electrician to run a new wire from the HVAC unit to the thermostat. If you’re looking to replace your old thermostat with a new smart or WiFi thermostat, you may face the problem of adding a new C wire/common wire (if your current thermostat wiring doesn’t have one in place).We’ve clearly explained everything about C wire in our detailed guide. if I put it in the ob the outside unit doesn't shut off if I put it in the y the heat doesn't work. Ok, my weedeater cut and tangled around two small wires running from the back of the outside AC unit into the house. Rc wires are only for air conditioning systems or dual transformer systems. Your AC compressor needs two wires - Y and C. Y comes from the thermostat and C comes from the air handler or the common side of the 24vac transformer. It is a red wire and comes from the transformer usually located in the air handler for split systems, but you may find the transformer in the condensing unit. If the existing Ac thermostat has four wires coming from your furnace and air conditioner unit, Then your new air conditioner thermostat must have four wires to connect to furnace and air conditioner unit. If you have heat and AC, you’ll need 18/5. The two 24 volt wires go to the R terminal and C terminal inside the thermostat. As power moves about the thermostat, it is controlled by various wires, which prevent the thermostat from delivering the power indiscriminately to any system. Cerrowire 500 ft. 18/2 Brown Solid Thermostat Wire (17) Model# 210-1002J2 $ 58 94. I have tried to connect the red wire and the black wire to to open spots on the inside control panel of the Central outside unit. Anyway, the setup behind the thermostat is Rc, G, Y1, W1, and now C. If the outside unit truly uses a C-wire, it does so for some low voltage electronics or on board controller. Please view my attached schematic for more detail. Once you clean the system, put back the float switch and your AC starts to work as usual. Cerrowire 250 ft. 18/5 Brown Solid Thermostat Wire (27) Model# 210-1005G3 $ 69 79. If they only go to the furnace, pulling a new cable shouldn't be too bad as they are only about 10 to 15 feet apart. The place I recently moved into has a 4-wire thermostat installed, but there are also two unused wires at the thermostat (one brown, one blue). Running New Thermostat Wire – It is possible that you may have to run a new thermostat wire from the air handler or furnace to the location where the existing thermostat is located. what i need to know is if there is a wifi smart thermostat that can manage with 2 wires and not add the C wire – i don’t have a basement or attic and all the ceilings are finished. Now it will not power up. You stand under the supply vents to see if you feel any air. Use these tips to wire a thermostat. Four wires come to the centrally-located thermostat from the main heating/cooling unit (usually located in a closet, basement, or occasionally in the attic): One wire, usually red, supplies 24 volts AC power to the thermostat, while the other three supply control signals from the thermostat, usually white for heat, yellow for cooling, and green to turn on the blower fan. The cable connection from the unit to the Power shutoff box and the shutoff box itself have all been rusted. These wires only connect to your cooling system. We noticed that our outside ac unit runs (the fan) even though the thermostat control is set to "off" inside the house. I have a red white yellow green and blue wire. Most thermostats require a battery, usually AA, to be changed out about once a year. Nest thermostat has power issues. Joseph Colombo says: February 22, 2015 at 5:38 am I purchased a lyric thermostat and followed the instructions to install. This is a BIG ONE! 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