Q: Knocking sound in passenger side under dash

asked by on September 14, 2016

When I start my car the only AC options on 3 and 4 (Semi high and high). The other two options 1 and 2 do not work. When I want the AC to turn on I have to hit the dash underneath where the passenger is. Once that happens there is a knocking sound that comes from that same area. What would I need to do to get every AC option working and to stop the knocking?

My car has 145000 miles.
My car has an automatic transmission.

Hello there, thank you for asking about your 2008 Mercury Sable. This sounds like it may be related to one of the AC vent doors. These can often times get hung up and create this kind of sound when they are trying to open and close but cannot. Try turning the vents to other options (i.e. from defrost to floor and back) to see if this changes it or makes the noise go away which can often times occur from getting a door stuck loose. If this does not work, I would recommend having an expert from YourMechanic come to your home to diagnose your car’s noises and make the necessary repairs.

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

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

Check Engine Light is on - 2008 Chrysler Sebring

Hello - the first task is to extract the problem codes that are causing your Check Engine light to be on now. Most auto parts supply stores will read the codes for you without charge. Once you have the problem...

my car is a Malibu 2008 stuck in neutral gear what wrong with it

If the gear selector is stuck in neutral, there can be a few causes. The brake light switch may be shorted. Also, the shift interlock mechanism may be out of adjustment or broken or the shifter linkage / cable may...

Heater not working and car overheating.

The first thing to check is if the coolant is low. This car is known to have a problem with the radiator leaking coolant on the sides and may have leaked most of the coolant out. This is why your...

Related articles

How to Quickly Cool Down a Hot Car
Knowing Knowing how to cool off a hot car that has been sitting in the heat and sun can save you the discomfort of having to sit in your vehicle's hot interior while driving to your destination. By taking a...
Symptoms of a Bad or Failing Refrigerant Pressure Switch (Sensor)
Common signs include the AC working intermittently or not at all, noise coming from the system, or warm air blowing from the vents.
How Long Does an AC Condenser Last?
Your Your car’s air conditioner system has a lot of different components, including the compressor, the receiver dryer, the hoses, the evaporator, and the condenser. The condenser is the component that converts gas into cooled liquid. Most people do not...