I have a '98 Ford F-150 XLT, 2WD, Short bed, Ext. cab, 4.6L, automatic trans. with 65,000 orig. miles. I bought this truck new. When I have the A/C or heater or just outside air coming in through the dash or floor vents, the air will switch to coming out of the defrosters when I accelerate and then…

The check valve is most likely near the heater and AC lines. It often has three ports, one to the intake manifold, one to a holding tank and one through the firewall to the dash control head. If they fail a generic check valve can be installed. All the McParts stores have the generic check valves in…

Check your vacuum hoses before replacing the check valve. For the price of vacuum hose maybe just replace them first.

There are also vacuum pods used to control various doors in the ductwork. A leak in a pod diaphragm can also cause a problem like this. Some of those pods are easy to access, others are not. I’m not real familiar with the layout on this particular model but with many Fords the pod that controls thi…

This sounds like the classic symptom of a vacuum leak. Keep checking all hoses and connections until you find the leak.

ok,I’ll look behind the glove box for something,I can’t seem to find what I’m looking for under the hood or I just don’t know what the thing looks like or where it is on the engine,

Ford used the “coffee can” for many years and may still. It can rust out just like its can cousins and have the same net effect.

Does anyone know where the “can” is located on my '98 ford F-150? I have looked all over and I can’t see a vacum can any where under the hood. Can’t see a vacum check valve either. I haven’t taken the clove box out yet, but I’m going to soon, also the cruise isn’t working anymore. Could also be a va…

The vacuum hoses in that truck are likely hard plastic tubes the diameter and stiffness of the cartridge in a ball point pen. The tube likely passes through the fire wall on the passenger side near the AC evaporator housing. Locate that and follow it back toward the the intake.

Vacuum check valve?

Maintenance/Repairs

Caddyman February 5, 2012, 5:15am 7

Usually, by removing the glove box, you can gain access to the heater controls

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Vacuum check valve?

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