To test the DC side: Set your multimeter to Dc volts Put your black probe on the blue wire labelled B- and your red probe on the yellow wire labelled Y. This is the signal coming from the thermostat to turn on the compressor on your air conditioner. You’re looking for something in the realm of 12V. If you don’t see 12 V then the problem is upstream and most likely with your thermostat. If you do see 12 V on the yellow wire then the next place I want you to look is on the green wire if you set th