A/c unit outside will not come on.

Sounds like you need a new contactor in the condenser. The low voltage is grounded. Remove the low voltage (likely 2 wires) at the condenser and wire nut the wires leading inside. With an insulated screwdriver manually push in the contactor and be sure both compressor and fan run. Then replace fuse and turn power on to air handler with a call for cooling. Obviously the outdoor unit won't run because you unhooked the low voltage but if fuse doesn't trip then it's likely the contactor. Good Luck

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The control voltage comes straight from the furnace or thermostat. Its 2 to 5 wires depending on if you have a heat pump or conventional system. If you have a control board on the inside of the furnace that has the terminal (y), then your control voltage will come from that terminal and the common terminal. Sometimes they have it connected to the (y) terminal from the thermostat, but will usually still be hooked up inside or right by the furnace. In (COOL) mode, the thermostat energizes the y and g terminals, (cooling and fan), which is sent to the outside unit on the contactor. You need 24v going to the contactor outside for it to pull in and make contact. If you have lost the low voltage, then it usually means bad transformer on the furnace (which nothing would work), faulty control board on furnace, faulty thermostat, or your low voltage wires could of been cut, chewed through, etc. If you do have the low voltage by chance, then it could be a faulty contactor on the condensing unit. I'm just throwing some things out there, its kind of difficult without knowing all the equipment you have. Have anymore questions, just ask. Good luck!

You will have to find the power source to your outside condensor unit(usually by the unit) and make sure you have power at the box and unit. My be contactor on outside unit or inside for low voltage(26 volts) on the main board. The contactor is the key as it will let you know if the inside unit is sending 26 volts to the contactor which pull in and activates the compressor/fan. If it sending the voltage but not engaging then it is the contactor, if it is not sending the voltage then it is a fuse or the main board. Hope this helps Tim

If you were able to check the voltage, did you check to see if you had 24volts at the contactor? Did you
have 220 volts coming into the contactor? If no to the
first question and yes to the 2nd question, take a
insulated screwdriver and push the contactor in, the
unit will run. You have a low voltage problem.

2nd, do not reference the 220 volts to ground, if you
dont have 220volts feeding into the contactor,
example read voltage between L1 and L2.

Remove the access cover from the outside unit. Find the contactor. It is the part that has the high voltage incoming wires attached. There is a button/bar in the center of the contactor. Use a insulated screwdriver or a wood pencil and push the bar in. If the unit starts you will have to trace the low voltage circuit from the thermostat and air handler to the outside. 24 volts should be present at the low voltage contactor terminals via the defrost board. If you have 24 volts to the defrost board,turn off the outside power, remove the red low voltage wire from the defrost board then reattach it. The board may be tripped on a low voltage fault.
Report back here with your result.

On A/C units, there is a low voltage line that leads to a contactor, which engages to close the high voltage circuit to the condensor unit. Over time, the accual contacts in the contactor can weld themselves together. Try shutting off your furnace breaker but leaving on the one for the outside condensor unit. If it still runs, your contactor probably needs replaced. Contact a licensed electrician or HVAC contractor and tell them you think your contactor is in need of replacement. Is a fairly simple and quick replace, but the contactor itself is not cheap.

no power will not let contactor pull in on outside unit - if capicitor is for fan and compressor and bad - neither will come on when contactor pulls in - low freon press. switch or if outside fan tripped unit on high pressure - could be manual reset - thermostat wires bad would not let run signal get to outside unit

If you have power to the unit and the contactor is pulling in ( low voltage side ) and neither compressor nor the fan comes on it could be 1 of 2 problems first check the wiring a mouse may have chewed through one of them, or 2nd your capactor is bad.

Ron
Cozy cool home comforts

Look at the contactor on the condensing unit, remove the low voltage wires to the contactor and turn on the system. If the low voltage fuse doesn't blow, replace the contactor.

A burned or pitted contactor will/can cause a unit to not run. Outside fan. Just thinking out loud. Start with low voltage check at t.stat then check outside low volt. Set t.stat to on. If fan engages at least your transformer is good. Next set calling for cool. Drop t.stat 68-70. If nothing happens go outside and with a screwdriver depress the contactor in. If fan and compressor kicks in change the contactor. If contactor is pulled in check outside fan. Remove the wires from the compressor and see if the fan will run . If it does you have eliminated start components as good. The compressor has to be check. It needs to be ohmed out. Turn off power at disconnect. Pull the cover on the compressor. Check between pins; then pins to ground. Open or infinite is good.Have you checked fuses. Like small 3-5 amp fuses