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: P1292 and P0181 come on when I hit a bump

If these two codes keep coming up together, it sounds like there is probably a spot in the wiring harness that is shorting to ground. P1292 is for an injector and the P0181 is for a fuel temperature sensor, so...

Q: Throttle position sensor - loose connection? 2012 Ford Fusion

Hello - yes, it is possible that the electrical connector for the throttle position sensor has a loose or poor connection. It is more likely that the throttle position sensor is failing. It has redundant circuitry, which accounts for some...

Q: Push button does not light up. All fuses are good good.

In addition to the fuse, there is also a relay for the rear defroster to make sure it is working properly (swap the front defroster relay for the rear one if the front is working properly as a check). If...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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...