1995 F-150 blower question

I just purchased this truck and while driving it today the blower would fade out when climbing hills and then come right back once the road leveled out and went back into overdrive. I've never driven an F-150 so I didn't know if this is normal or if there is something in particular I should look at to fix it. Thanks.

I wouldn't be thinking about fixing it just yet. When going up a hill the overdrive shifts down and the engine rpms go up. The increased output of the alternator could be sensed by the voltage regulator and could be compensating for it. Another thing that could be causing this is the drive belt. It could be slipping going up a hill and could be causing the fan to blow less. Do you have a battery light that goes on while all of this is present? I would check the drive belt for the alternator. It should have only about a quarter inch of deflection and shouldn't be cracked or glazed.

Are you speaking of the AC/Heater "blower"?
If so you have a vacum leak.

Yes, it's the a/c blower. I did check the belt and it was in good shape and tight, and no warning lights come on. I did a little research on the vacuum leak suggestion and I checked all the connections and hoses as far as I could see them and they all seem to be ok. During my research someone mentioned a "check valve" but there was no elaboration on where it is or what it may look like. I'm not even sure if my truck has one or if the person who posted that was even right, but I thought I would mention it if it was a possibility.

Does it sound like the blower motor is actually slowing down, or does the airflow out the vents just get weaker? I think ghink hit the nail on the head. Check the plastic line that goes thru the firewall to the heater control valve. It should be on the passenger side around the blower/evaporater housing. Theyre bad about cracking and leaking and around here we have a problem with rats/mice/squirrels chewing on them, from idle up to cruise(unloaded) vacuum is normal and theres enuff to overcome the leaks. When you go up hill/accelerate (loaded) the vacuum drops off and the air doors move changing the airflow.(maybe to the floor or defrost and it may seem like the motors slowing down because theres less air coming out the dash vents) . It could also be a leak at the valve on the dash control panel. Make sure you have good vacuum coming out of the vac reservoir going to the firewall, it should be at manifold vacuum. It may be the motor, but most of the time its vacuum related.

On my 2001 F-150 I found the vacuum reservoir line rotted where it connected to the reservoir tank located under the battery. It's accessible from underneath on the right front passenger side.

I finally found the problem! I bought a vacuum tester and dove into checking all the vacuum lines all the way to the A/C controls. I found the black one that went thru the firewall was really loose where it connected to the back of the controls and also the white one that passed thru the firewall under the hood area was dry rotten....it was VERY hard to tell it until I bent it a little and thats when I noticed how bad it was. I put some heat shrink tubing over the white one temporarily and I used a change over fitting to upsize the black one so it would fit tighter. Test drove it and it blows out the vents constantly now no matter what the RPMs are. Thanks for all the help! I appreciate it! Now I can move on to the next project of changing out the key switch this weekend. From what all I've read on the net, it doesn't sound like a very difficult job so we'll see. ;)