Q: AC/heat suddenly stopped working

If no air hot or cold is blowing from the vents, there are a couple of possible causes. Air is moved through the heating and air conditioning system by the blower motor. Typically the blower motor is located on the passenger side behind or under the dash and covered by trim panels. The blower motor itself operates on different speeds by using s resistor which varies voltage to the motor itself to vary speed. Less voltage means slower blower motor speeds. Higher voltage means higher blower motor speeds. Typically blower motor resistors show signs of failure with certain blower speeds not working. For example, the blower bay work on speeds 1,2,and 4, but not on 3. It is possible however, for the resistor to fail entirely and provide zero voltage to the blower motor no matter the speed settings. Also, the blower motor itself can fail to operate no matter whether the resistor is providing voltage at every speed setting or not. Also, it could simply be a blown fuse or bad relay not sending any power at all to the resistor or motor. Have a certified technician inspect your heating and air conditioning system to find the correct fault.