Working on the old girl and noticed that the a/c compressor was not engaging,so I ran a jumper wire and it engaged. I started looking in the top of the cab and after chasing power everywhere with nothing coming out of the cut out relay to the compressor. I changed it still nothing unless I unhook the ground and then it cycles but the fan does also but only on purge, put it on high and compressor and fan runs continuously. Could it be fan speed switch or something else I have replaced the thermostat switch also with no success. Thanks for any suggestions.