1996 chevy Silverado 5.7 ac compressor will not click on we charged the system checked the fuses and changed the relay switch ,,it will turn on if we put a test light on the relay switch .. the compressor runs and blows cold ..at a cross roads
There are other switches that help control the cycling of the compressor. Check the operation of the low pressure switch and the high pressure switch for proper operation. The low pressure switch will turn on the compressor when the low side pressure is above 25 PSI and the high pressure switch will turn off the compressor when the pressure is too high. The contacts on the high pressure switch will be closed completing the electrical circuit when pressures are normal (below 400 PSI).
The PCM controls the path of ground for the compressor when all of the input sensors are working properly or in range. If all pressures sensors and the A/C control module are working properly and the A/C pressures are correct then the PCM could be the blame.
You didn't mention what kind of gauges you were using; a good set of professional gauges are the best to use if available.
I am supplying wire schematics for the A/C clutch circuit from the Alldata automotive information website below.
If you have any other questions get back to me we can diagnosis the problem further.