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Gagootza is correct. It's more than likely a stuck or welded contactor. Unless you are very familiar with wiring 230-Volt circuits that use controls with low-voltage coils, I would recommend calling out a pro to do this repair for you. If this is a very old unit, like the old round Carrier units, you may have a contactor that uses either 110-volts or 230-volts for the "primary" coil on the contactor. No matter what type of contactor your condensing unit uses, you want to make sure that the replacement one has the correct coil voltage rating and you want to make sure that the amperage rating on the control is correct. There are single-pole contactors, there are two-pole contactors and on larger units or 3-phase units there are three-pole contactors. If you install the wrong contactor, you will have a problem. If you install the correct contactor the wrong way, you can cause your unit not to function or you can burn out your compressor windings if you wire it incorrectly. I highly recommend calling a pro, unless you know exactly what you are doing.

there is a contactor thats stuck on the condensor which turns on the fan and the compressor.turn the power off take the cover that covers the electric on the condnsor.you will see a big black thing that looks likw a b H, that's your contactor.in the middle there is a black bar that goes across,is it pulled in.if it is and the power is off, then it's no good.if you change it buy one like it and when wiring it.do 1 wire at a time,hold the contactors side by side and do one section of wires at a time and you can't wire it wrong,you can also take a close up picture of it and use it as referance to the wiring.does the furnace go off when room temperature is reached,if not,you might have a bad thermostat