Auto Air Conditioning & Heater Repair: 02 Civic LX, honda civics, master switch

Question
02 Civic LX, was taken to a local shop where the $59 a/c special turned out to be $180 and more damage to car. My sister finally let me look at it, and I replaced the bad service valve, but now have to figure out what the shop damaged. When it came back, the A/C and (back glass) defroster switches are slightly illuminated all the time, and have no visible change when depressed. The glass defroster does work normally.  The A/C does not come on when the blower is set to defog. I checked the fuses (under hood and dash), and also swapped the A/C relay with a known good part. The system is properly charged, the pressure limit switch is working fine, but the compressor won't engage. I jumpered it from the battery, and the clutch pulls just fine. There are no idiot lights on. What's next to check?

Answer
Hi Brian

On the Honda Civics It is common for the master switch to go bad.  The light may have just gone bad.  Check your thermostat at the evaporator.  You will have three cables one should be power all the time.  The other two should be ground with the ac button pressed on.  If you turn the button off the ground should turn to power.  If you see a difference in power ( positive to negative) when you push the button then your master switch is good if not more than likely your switch is bad.