I have a 99 deville ,the ac compressor , ac***ulator,orifice tube were replaced before I got the car the owner said the compreesor has not worked since then.The DIC has an service ac message flashing ,there are no codes in the PCM,I tried resetting the ac system by disconnecting the battery negative cable for 30 seconds this did not resolve the problem,next I checked the low pressure switch with a 12 volt test light it had voltage at both terminals,I grounded the compressor relay and the compressor comes on but not the cooling fans,I subistuded a known good ac control head on the I.P. this did not resolve the problem either,I also checked the ac fuse,comfort fuse,cruise control fuse with a 12 volt test light they were all good. the system has 80lbs of pressure with R134.
please help