Skip the auto shop - Our mechanics make house calls

Q: Ac & heat only blow out of defroster when I turn the

asked by on

When I turn the heat or Ac on, no matter which setting I choose it only blows out of the defroster, won't blow out of vents or floor

My car has 203000 miles.
My car has a manual transmission.

A: It sounds like you have a problem with the ...

It sounds like you have a problem with the vacuum supply to the HVAC control head. Engine vacuum is what changes the airflow to the vents and floor. Defrost is the default position when there is not a vacuum source.

  • The first place to look is under the hood. Look for any vacuum lines off or damaged around the intake manifold.

  • Next, check the vacuum reservoir above the splash shield in the RF fender (plastic tank). Check for cracks or broken nipples. (If you have 4WD, this also supplies vacuum to engage the hubs and transfer case. If the there is a leak in that system, the HVAC will be affected.) From the plastic tank, a vacuum line runs to and through the firewall into the dash.

It’s possible the you have a leak behind the dash, or a bad control head, but a problem under the hood is more likely. If you need assistance in locating the problem, consider YourMechanic. A mobile mechanic can diagnose the issue with your AC system at your home or office.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: Rough Starts & Idle

The fuel pump code for the secondary fuel circuit fault may be the fuel pump module on the cross member under the truck. The module can go bad and cause no fuel pump operation intermittently. The engine vacuum line from...

Q: ECU is disconnected and I can't program a new key. I lost the original key

Hi there. For your vehicle the ECU is showing a battery disconnect to the ECU for either a loose battery cable or a loose connection. Check the battery terminals and make sure that they are tight and clean from any...

Q: Defrost button wont come on. Control power button doesnt work.

It seems like the defrost of the vehicle has an issue. There are several possibilities that could cause this. The control unit for the climate control system could be malfunctioning. The fuse for the rear defrost could be blown due...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
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...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.