98 ram 2500 Blower diverts to defrosters

[Big Minnow]

Hi,

I've got a 1998 Dodge Ram 2500 4wd 360 5.9l gas.

When I accelerate all the air from the blower diverts to the defrost. When I let up air diverts back to normal.

I've taken ether and sprayed around everywhere I could think of looking for vacuum leak but no luck. Any ideas?

[Jeremy airjer W]

Probable your vacuum check valve for the HVAC. it is located on the passenger side of the plenum about in the middle. If you find the vacuum hose that goes through the firewall on the passenger side and follow that hose to the engine you should see the check valve about right where the 90 degree elbow is.

[PurpleFloyd]

Had a 98 ram 1500 5.9 that did the same thing . I think it is fairly common and as said above it was a vacuum issue.

[Big Minnow]

I had heard of that before but couldn't locate the check valve. I'll look again. Is that a generic vacuum check valve or a specific Dodge part, when I do a search for vacuum check valve for a '98 ram, on an auto parts store web site it returns a no parts found reply?

[Jeremy airjer W]

It will be a black or white disk about the size of a quarter and about a 1/4 inch thick. If part stores have them it would be in. Help pack and may not be in the online database.

[Big Minnow]

Thanks for the help.