Air conditioner compressor only works in defrost. In the a/c settings compressor will not cycle but when you switch it to defrost the compressor cylces fine. i have not put gauges on to check the pressures yet

It will run for a period of time when a defrost mode is selected. Suggest you try a heat mode other than defrost and see if it stops.

May be a bad switch.

If you are getting heat inside the car, the defroster should also work. There is a control switch problem that doesn't switch to defrost from heat, or the compressor for the air conditioner is not functioning...it provides heat for defrosting as very dry air to the heater box.

Does it shut off, like the electrical system shuts off and the engine slowly stops (the same as when you turn off the ignition)? Or does it stop abruptly and with a noise, like a squeal or thunk? If it is the former, then it is a short (or bad ground) in your air conditioning system. If it is the latter, then, yes, it could be the compressor bearings are seized.

Check for a fuse that indicates radio and replace it if it's burnt through or melted or discolored. The Buicks have dash controls that require expensive repairs sometimes to get the temperature controls to work so some people jump around the controls by installing a separate toggle switch that directly turns the AC unit off and on for 92 through 94 Buicks. Any AC shop can install the bypass wires.

The Air conditioner compressor is seizing when the compressor clutch trys to engage. When you put on the defroster the air conditioner automatically comes on to take humidity out of air.

Fuse 9, 50A under hood, Fuse 5 15A Instrument panel. If they're ok, make sure the compressor clutch can be turned by hand (engine off, obviously). If not replace the compressor. Most common problem is the cycle switch. That should be the electrical connector on top of the accumulator. Just jump that by backprobing the connector on both sides with a pinand connect them, with the car on and a/c on if the compressor clutch engages, replace the switch. If it doesn't, try wiggling wire harness and watch it, if it engages, find a broken wire and repair it.

ok could be one of 3 things. 1 you may be out of freon. (proly spelt that wrong) 2. compresser could be bad. 3 the clutch on your compresser might not be engaging. when trucks running turn ac on and see if the front of your compresser spins or not. if it does clutch is good. but it could be that your compresser is still bad. either way i recomend you go for freon and start there. when they fill it they will tell you for sure wether or not your compresser is bad.

AC is supposed to run in defrost position It should not run in heat position.

Is 1 of the 2 AC (under the hood) lines cold? if so you may have a blend door problem, that door is in the dash air duct distribution system, it mixes are between the hot heater core and the cold AC evaporater core to give the set or desired air outlet temp, When you turn the defrost on does it blow hot/cold as the lever is moved back and forth? The compressor turning off and on is normal cycling of the system, when it reaches a preset pressure in the low side line, a pressure switch will open and compressor will "cycle off" when the press starts to rise to a preset limit the compressor will "cycle on" and so on. I assume you have an electric bled door, older cars and trucks use a cable operated mechanical door.