Problems with low voltage control wiring turning on cond. unit

Hello, you need a wire on w,g,r,y at the thermostat subbase, and the same thing on the control board inside the indoor unit. Then you need a wire from the y and c terminal on the inside unit and attach it to the outdoor units contactor coil low voltage side.

You need to get low voltage wire known as 5 wire. run wires thru wall to stat and furnace Red wire goes to R terminal white to W terminal Green to G terminal Yellow to Y terminal on both the stat and furnace circuit board. Now you need a wire called 2 wire low voltage wire run that from furnace circuit board to outside A/C. At furnace hook red wire to Y terminal and white to C terminal doesnt matter which ones you hook up at outside unit. Do it just like i told you this will work properly.
If this helps please rate me.

Hi, from what you are saying, it sounds as though you have a control/thermostat problem. You say it doesn't work right, so I am assuming it does work, but just does not come on when the stat calls for heat. Make sure you have 24 volts to the stat. Turn the fan to the on position to see if it comes on. If so, you have power. If the heat is not coming on at 66 degrees, and you have it set to call for heat below 72, you do have a problem with this stat. The room sensor is mounted in the circuitry of the subbase, or second section of the thermostat. There is nothing you can do to repair this stat, your only option is to replace it. If you have both heating and air, you will need a stat for that. If you have gas heat get a regular central heat and cooling stat, 24 volts. If you have a heat-pump, you will need a heat pump stat. The best thing to do, is shut off the power to the indoor unit. Remove the first section of the stat, it should just unsnap. You may need to pull some to get it off. Then you will see the subbase with the wire terminals. If you have gas heat, it will be marked something like this. RH to RC with a red wire connecting the two. You will have a smaller red wire coming in from the indoor unit which can go to either one. You will see Y yellow for cool, W white for heat, G green for fan. If its a heat pump stat, you will have many more terminals such as o/b, may have E and C, w-1, w-2. Draw you a diagram of the wiring and the terminals they go to. Now, remove the subbase. It will be held to the wall with a couple of screws. Take it with you, and go to Home Depot, Lowe's Hardware, O.S.H. to get a stat. Try and find the same one, but it will not matter as long as you have the same terminals. Many stats will work on many units. Install it in the reverse order. This drawing is very important for you. This will indeed solve your problem, and is very simple to change out. If you have any questions when doing this, please contact me, as I will check in on you. It may take time for me to respond if I am on another call. Please don't forget to rate me on this, I know you will be kind! :))
Sincerely,
Shastalaker7
A/C, & Heating Contractor PS, Don't loose the manual for your new stat!! Put it in a safe place, this is very, very important.

check for voltage then check connections sometimes the wire breaks and no power gets to the stat

Depending on the thermostat you have, there may be an issue there. Some stats have a subbase that controls the fan for AC. I would like to know the model of your stat

the unit with3 wires was set up as a dual transformer the new unit is single transformer system. it needs to be rewired at thermostat,furnace,and ac

Defective thermostat wire.
Defective contactor.
With the t-stat set for cool and turned down on a low temperature, check for 24 volts at the contactor low voltage hookup. If you have 24 volts, replace the contactor.
You can manually close the contactor to make sure the high voltage is going through it.

either the gas at the outside valve is off, or the gas valve at the furnace may be off, or the switch on top of the gas valve in the furace may be off. if they are all on, then you may not be getting a call for heat from the stat to the furnace control board. check to see if you are getting a 24 volt signal from the stat to the w terminal and common terminal on the furnace board. if you are then check to see if the voltage is arriving as 24 volts to the wires at the gas valve itself . if it is then the gas valve is possibly bad. if it is not then the board is possibly bad.look for loose or broken connections on the low voltage wiring. most unusual that the board does everything else but send power to the gas valve. you need to zero in on the valve i think and start by turning off power and that should restart the sequence of operation and you can observe it step by step . if you are not getting a call for heat then the stat may be bad be sure you are in heat , fan in auto and temp pushed up to max. if no 24 volts is sent to furnace board white and common low voltage board then stat is bad. remove it if you think its faulty and jumper the white and red wires together on the subbase. that duplicates what the stat normally does. if the furnace lights its the stat. having said that i realize the stat has to be sending a heat signal or the other stuff would'nt start. so..... back to the furnace board. check that 24 volts in from stat and 24 out to valve and that will put you on your problem item. good luck

you should have 24 volts between yellow and white wires at the stat when the stat is set to heat and set as hot as it will go. burners should light first then 3 to 5 minutes later the fan motor should fire up. if burner doesn't light check the wires going into the top of the gas valve see if you have 24 volts arriving there from the stat. if you do then the gasvalve is probably bad. you can bypass the action of the stat by jumping red to white on 90 percent of the stats made and in a few seconds the gas valve should click open gas flow to main burner where pilot ignites it. another easy check you can do is flip stat fan switch to on. fan should come on at once. if not then you have either no high voltage to unit or no low voltage ( as in a bad transformer). if the fan comes on you know you have high volts and low volts...by cover i assume you mean the decorative cover but there second cover with the mercury bulbs and all is still there. if you have only the bare subbase then new stat time. sounds like an old furnace if it has a standing pilot, it should be checked for cracked heat exchanger by a pro with a n electronic carbon monoxide detector. NOT a diy item due to the real danger of co poisoning.

to see if it is the t-stat or the system you can unwire the entire t-stat and jump out the wires. never touch the blue to any other wire or you will blow the low voltage fuse on new board. if you jump red to yellow and your condensing unit cycles on the t-stat is wired wrong or wrong style. If not go check the yellow wire at cond. unit and see if power is even going to it.