88' Accord a/c clutch won't engage

I have a 1988 Honda Accord LX. The A/C has quit working. I am familiar with
general mechanics and have checked the following items. It has 45lbs of
pressure on the low side. I bypassed the low pressure switch just to make
sure. Nothing changed when I did this. I checked the relay that engages the
clutch and it is good. On the inside of the car when I push the A/C button
the green light comes on and one of the radiator fans come on. While doing a
circuit test I have found the following. There are 4 wires that connect to
the clutch relay. The wire (red) from the relay to the clutch is good. The
hot wire (yellow w/black stripe) going to the relay has power. There is
another wire(also yellow w/black stripe) that also has power, so the 4th
wire (yellow) has to be a switched ground to engage the relay. This wire is
open when tested. What controls this wire? Is there something else that I
need to check?

Thanks, Wayne