You might want to see where the ground wire for your capac meter goes. One terminal on the meter is to the sensor through the pushbutton, the other goes to the hull. It should go directly to the hull. If it shares a ground with the blowers, then the capac reading will be affected.
If your blowers use the hull for their return, add another wire back to your ground at the battery.
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida