Hansberger Refrigeration Blog: Your AC Repair Resource

How HVAC Contactors Function Within Your HVAC System

HVAC ContactorsHVAC contactors are essential AC parts that switch the flow of high-voltage electricity to certain systems located in the outdoor unit of your central air conditioner. These components, namely the compressor and condenser coil fan, require 240-volt electrical power, which is twice the voltage of other components in the system.

How HVAC Contactors Work

When on standby, only low-voltage components in the outdoor unit receive power. However, when the indoor thermostat sends a signal to the air conditioner to actuate a cooling cycle, the contactor energizes and switches 240-volt power to start the high-voltage compressor and the fan.

Later, when the temperature setting inside the house has been achieved, the thermostat sends another signal, and the contactor disconnects power from the compressor and the condenser fan. These components revert to standby mode until the next cooling cycle.

When Contactors Fail

Contactors have a finite life span. They are vulnerable to wear and tear like most any component that incorporates moving parts and high-voltage electricity. Depending on how much use the central AC receives and whether or not it receives annual preventative maintenance by a qualified professional, HVAC contactors can be expected to last five to 10 years before it becomes defective.

Signs of a failing or failed contactor includes:

  • A “chattering” noise from the outdoor unit every time the central AC cycles on.
  • A loud humming sound emanating from the outdoor unit, though the unit does not cycle on at all.
  • The outdoor unit does not shut off even though the programmed thermostat temperature setting has been achieved.

What Not To Do

For safety’s sake, don’t attempt to repair or replace central AC contactors yourself. Due to the dangerous high voltage involved, this is not a DIY job. It should be left to a qualified HVAC technician to diagnose the problem and, if necessary, replace the defective part.

For certified, professional service to resolve issues with HVAC contactors, the experts at Hansberger Refrigeration and Electric Company are ready to respond.