How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Brian HVAC Guy Your Own Question
Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 922
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
Type Your HVAC Question Here...
Brian HVAC Guy is online now
A new question is answered every 9 seconds

My ac unit is not running outside trying to diagnose a pr

Customer Question

my ac unit is not running outside
trying to diagnose a problem
Submitted: 2 years ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 years ago.
Hi I'm Brian and I'm here to help! The humming you hear is probably the contactor being energized by the thermostat with control power from the indoor unit. The fact that nothing is running usually indicates no line voltage power but could be other things. You could have a bad contactor or even ants under the contactor points (believe it or not that is extremely common!) I could be that you only have 1 phase of the 2 phases of line voltage coming into the unit. You should check for 240 volts ac nominal on L1 and L2 of the contactor. It will be the two line wires that come into the unit from the disconnect. See if either of those issues may be the case and let me know what you find and we can go from there. Thanks, -Brian