Q: AC causing knocking sound.

asked by on

The AC and heater will work sometimes on all levels on the switch. Both will produce hot and cold air. But then the AC/heater system will not work at all. If my truck sits a while, the system will work. When I start the AC, I can hear a knocking sound from under the dash.

The knocking noise is the temperature blend door actuator trying to move the blend door. The actuator would need to be checked and replaced. I recommend having a certified mechanic, such as one from YourMechanic, come and inspect your vehicle’s AC system for you. They will be able to repair or replace any of the components to get your AC functioning like normal again.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. AC causing knocking sound.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Engine rattled, something fell out, and engine died

Hello. I would go ahead and follow the dealership's recommendation and have the updated water pump installed. I would also recommend having the belts, and any other pulleys, replaced if possible. If the vehicle is still under factory warranty then...

Q: Air not working after alternator repair

There is a chance that the electrical connector that goes to your AC compressor may have gotten disconnected while the alternator was being worked on; it is in close proximity to the alternator and may have been bumped. I would...

Q: 1.69 amp parasitic draw, previous owner had hitch. Everything stock

The best way to find the draw is to pull fuses out one at a time. This isolates which circuit needs to be diagnosed. You may have a module (computer) that is not going to sleep. I found a technical...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...