Blower fan

On my 1998 Lumnia when I run the air the fan runs great but when I step on the gas to pick up speed the fan slows way down or maybe even stops. Anyone know what causes this. thanks for any help.

Are you sure that the fan actually slows down? Or is it maybe that it changes to blow out from a different place (e.g. from the panel to the defrost?) If it changes to flow out a different duct this can often sound like it slows, and it would be cause by a leak in one of the vacuum lines that control the air flow.

I second cigroller.

I third it.

Thanks guys I’ll check it out further. Where would this vacuum line be located, under the hood or under the dash

Yes, it runs from under the hood to under the dash to the climate control unit. From there several vacuum lines run to the air door servos.
In addition to the possibility that it is a vacuum leak, I would add that it could be a defective vacuum check valve instead.

If your engine is worn out the vacuum may be dropping too low to keep your blower doors open. If that’s the case you will just have to live with it.