AC blowing out defroster

Thanks Mr. Wizard will look when I get home....

If there is a vacuum leak, the motor tends to run a little rough at idle.

Clay, all HVAC units in vehicles by default use the AC to help defrost. If a major vacuum leak occurs, the HVAC unit will also default to all air blowing on the windshield.

If you are not real handy and if you do not have a Mighty Vac or some other hand actuated vacuum pump, you are probably better off going to an AC shop.

The vacuum for the controls comes from the intake manifold. Find the vacuum canister and trace the line back to the engine. The vacuum that goes to the HVAC controls is the line going to the dash.

Engine pulls vacuum, hoses to and from the canister and the canister reach a max of about 20 inches and closed valves and check valves keep it from leaking out. The register control, will generally have four or fives vacuum lines going to the vacuum actuators or motors.

Start with a vacuum gauge at the controls side of the canister. If that vacuum will build to about 20, turn off the engine and see if it will hold its max. If it won't the leak is between the canister and the engine.

Just keep following the lines to the controls. Test each one and eventually you'll find a leaking actuator or hose.

You are going to need to remove the bezel and HVAC panel to get to the vacuum selector valve and find how they are run.

It's is a simple system in a very inconvenient location. Small hands are a plus most of the time. You may be able to access the valve and hoses by lifting the dome that has the instrument cluster and looking down toward the control panel.

Good luck and the hand vacuum is anywhere from $20 to $30 bucks.

Here is a generic diagram of vacuum controls.

he said GAS burner in the first post

most gasers draw vacuum from a port on the intake manifold, NO PUMP

on my DP the vacuum pump is little gizmo under the dash

Doubt you have a Diesel engine.

Where is the vacuume pump I can't find it

Thanks hikerdogs walking out now to check.

DaveG39 wrote:
There was a problem on Ford Chassis around that year with an inadequate vacuum reservoir and was a recall years ago to replace the reservoir. If there is insufficient vacuum, the system causes the shutters to close to living area and default to defrosters so you will always have air to windshield. I had that on my 2001 Dolphin years ago.

I don't believe there was ever a "recall" for this problem. I do believe however there was a Ford service bulletin issued. Recalls involve safety items. The heat/AC system is designed to provide windshield coverage in cases where vacuum is lost, so there would be no safety issue.

Service bulletin items are in many cases covered by the factory when the vehicle is under warranty. However I doubt they will still cover something on a 15 year old vehicle.

On the bright side the problem is more often caused by the vacuum line being knocked off the reservoir port when service is performed (or when checking the oil level). The spherical tank should be located in the center of the vehicle right to left, and above the hood opening. You'll probably have to stick your head inside the engine compartment and look up. There should be a small diameter blue hose with a clear fitting that connects to the reservoir.

There is also another vacuum reservoir attached to the frame just below the right headlight. This reservoir has nothing to do with the heater controls, but if the connector has come off or the tank is rusted out the engine may not be able to produce enough vacuum to supply the heater controls. Generally if this tank or connector fails it will turn on the "check engine" light. However I have seen cases where it didn't.

Defrosters always use the AC to blow dry air.

Didn't know about the recall thanks......and also forgot about the old juice can under the hood...will start a Nader the hood...thanks for the quick response