1997 Deville ac compressor locked out - low

Either connection is bad to low pressure sensor or pressure sensor is faulty.

Does the AC system show normal pressure readings and maintains at least 28-32 PSI on the low side charging port?

Air in the system
Low on refrigerant

The compressor should come on at about 32 PSI, so you have either a low charge or a defective fixed orifice or a clogged system.

CHECK REFRIGERANT CHARGE. USING A MANIFOLD GAUGE SET. HOOK MANIFOLD GAUGE SET TO LOW PRESSURE PORT AND HIGH PRESSURE SIDE PORT. LOW SIDE PRESSURE SIDE SHOULD HAVE 25 - 36 PSI AND HIGH PRESSURE SIDE SHOULD BE 178 - 237 PSI. IF LOW SIDE PRESSURE SIDE READ BELOW 20 PSI THE LOW PRESSURE SWITCH WILL NOT TURN ON THE AC COMPRESSOR CLUTCH NEED TO ADD LITTLE MORE REFRIGERANT. IF REFRIGERANT LEVEL CORRECT CHECK AC COMPRESSOR FUSE AND RELAY.IF POWER GOING TO AC COMPRESSOR CLUTCH YOUR COMPRESSOR CLUTCH HAS OPEN WINDING. AC COMPRESSOR CLUTCH NEED REPLACING.

NOPE STOP CHARGING DONT PUT NO MORE REFRIGERANT IN SYSTEM.DO GOING TO DAMAGE NEW COMPRESSOR AND THE EXCESS PRESSURE WILL BUILD UP CAUSE THE REFRIGERANT CANISTER TO BURST EXPLODE INJURY OR FATALLY HURT YOU. BEST TAKE CAR TO A GARAGE.LET GARAGE PUMP DOWN AC SYSTEM AND CHARGE UP.BECAUSE YOU WILL DAMAGE NEW COMPRESSOR. MOST OF TIME I WILL HOT WIRE THE AC COMPRESSOR. MAKE SURE COMPRESSOR HAS 2 OUNCES OIL IN IT.IF COMPRESSOR START UP NO OIL IT WILL LOCK UP.DONT KEEP PUTTING REFRIGERANT IN THE AC SYSTEM, THE R 134A GOING TO FREEZE UP TOO MUCH MOISTURE IN SYSTEM YOU HAVE TO HAVE A VACUUM PUMP TO PUMP DOWN AC SYSTEM CHECK FOR LEAKS BEFORE CHARGING SYSTEM UP.LOW SIDE NEED TO BE 31 - 36 PSI THE HIGH SIDE SHOULD BE 165 - 205 PSI.

100 AT PSI ON THE LOW SIDE TOO MUCH REFRIGERANT.LOW SIDE NEED TO BE 28 PSI. HIGH SIDE SHOULD BE 200 PSI.YOU NEED A MANIFOLD GAUGE SET TO SEE YOUR LOW AND HIGH PRESSURE SIDE.YOU PUT TOO MUCH REFRIGERANT IN AC SYSTEM IT WILL EXPLODE CAUSE SERIOUS INJURY AND DAMAGE THE COMPRESSOR.

Check system hoses. Try re-charging refrigerant.

To diagnose problems, an A/C manifold gauge set is needed to read high and low side pressure readings. Avoid adding refrigerant with a simple charging kit like the ones sold at parts stores. Don’t add any stop leak, this can cause problems in the compressor, expansion valve or condenser.
Keep in mind that using an A/C gauge set and seeing BOTH high and low side readings can help in diagnosing the problem when you know what to look for. First, on a 134A system the high and low side service ports are different sizes. AC gauge sets have color coded hoses, the blue color coded hose has a connection that fits on the low side service port and the red hose has a connection that will only fit onto the high side. The yellow hose won’t hook up to anything if just checking the readings; it can be used to connect to a vacuum pump or attached to a refrigerant can or tank.

Normal readings on high and low side with AC OFF (static pressure) - Depends on outside temperature, but normally is between 80-105 PSI
Normal low side reading with AC on high speed and MAX & engine at 800-1000 RPM’s - Ranges from 25-35 PSI - Note that on many Chrysler products a normal reading on the low side may be 15-25 PSI
Normal high side reading ranges from 200-350 PSI

Don’t assume that if adding little Freon is good that adding a lot is better!  Overcharging just a little can decrease the performance of the system and possibly damage the compressor.

Both low and high side readings are lower than normal, this indicates a cars AC system is low on refrigerant and is under-charged.
If both low and high side readings are too high, this indicates an overcharged system - too much refrigerant. This also can indicate that the condenser fan is not working, is too slow or the car is overheating and heat is transferring from the radiator to the condenser.

Good luck and hope this helps, keep me posted be glad to answer any question you may have. And yes the A/C system on your car uses R143a and there is a A/C pressure switch along the low pressure line or on the accumulator, it looks like a oil pressure sensor with a two wire lead cliped on it. 

Static pressure(Non operating) usually is around 70 lbs and should be even on both sides. Sounds like the systen is too low for the computer to allow operation. I suspect a small leak somewhere. Adding as little as 1/2 lb should allow operation and leak testing.