Ok, I know it is probably a vacuum problem somewhere, but I cant work on my truck until Wed. I thought I would ask you all knowing guys what I should do first with this.

When I am driving my truck on the side streets the heater blower works fine no matter what I am doing. Once I get on the highway and am going at least 60mph everything is fine, it is when I start up a hill or a slight hill where I have to give the truck more gas. When I do that the fan is still blowing but nothing is coming out of the vents. I figure it is a vacuum line that switches the climate control to off or some other position. My question is, what line am I looking for and what would you check first besides disconnected lines and rotted lines. Thanks

1995 f150 5.8 with AC.

 

A broken white vacuum line under the hood on top of the heater box.

 

Okay thanks I will check that.

 

Subford is on target with this.
Mine had a visitor gnaw on it and left me with white dust. I cut it back to fresh line on both sides and slipped each into a section of windshield washer hose. (Same I.D. as the O.D of the white plastic...) No clamps, etc.

 

Thanks again for the help guys. I was able to get a few minutes and look at the line you are referring to. Sure enough there was a hole in it and it seems brittle. I taped up the hole for a temporary fix (hopefully) I will be able to tell when I drive home after work if it was a good temp fix or not.

 

My 94 5.8 did that for a while one time, but it was the A/C not the heater. It turned out to be my low coolant level. If you are using the defrost as heat it might also be your truck is low on coolant.

 

Good advice and a definite possibility since I just did a thermostat r&r. Thanks

 

Low Coolant will not stop air from coming out the vents.

 

Ain't that line for the door to the heater? If that's messed up the door won't work right...but again, the issue doesn't happen all the time, right?

 

Well I taped up the hole in the line, but it still does it. For clarification it happens when I am trying to maintain speed on an uphill on the highway over 50-60 mph. Could it possibly be the actuator?

 

The problem is a vacuum leak somewhere. It could be the lines or even the reservoir. The fan doesn't shut down, instead, the loss of vacuum to the blend door causes it to fall back to its default position, which is defrost. Long periods under hard throttle (such as uphill) mean there is little vacuum in the engine, so vacuum-actuated accessories have to rely on the reservoir. If there is a leak, it will bleed down in short order.

Jason

 

Okay. Hmmm what does the resevoir look like?

 

it's round and black and on the passenger side fender skirt - probably looks like a coffee can

 

I may just replace the line for the opening and closing of the door. It is pretty brittle.

 

Oh that's what that is...lol I always chuckle when I see it. I imagine the people who built the truck would drink a lot of coffee and use the empty cans to put in the truck....lol spray painting the thing black first, of course.