Has anyone one on here had their truck lose air flow fromm the vents after driving for an hour or two? I have lots of air flow at all the settings(defrost,floor,panel) then it gets less and less. I removed the plenium cover only to see everything in good working order. I replaced the 3 vacumn motors along with the vacumn line going through the firewall to the vacumn tank behind the battery. As well I replaced the two vacumn check valves on the firewall side.

I still hear a slight wssh, wsshhh noise, and recently had a 4 hour drive in extremely cold weather. Well, the passenger side dash above the glove box became extremely cold as the airflow kept decreasing. I have put in new thermostat and have great heat, just no airflow coming out. When I stuffed a jacket under the passenger side the airflow came back. I replaced the blower motor and it does switch on all speeds high, low medium. A gasket came with the blower motor, didnt look to be in good shape, had a big crease in it and since I seen no old one I left out, could this be the problem?

Perplexing dilema. Any help at all would be appreciated, thinking I am going to have to remove the dash again. The blend door, which noted on this forum as a problem , looked fine and I am sure it is working as I can change temps. The wshh wsshh sounds seems like it is originating from under/behind the glove box, although the only two vacumn lines behind it are the one main supply, which I replaced with new and the one for the damper motor which I replaced with new.

I did notice on the firewall, battery side, there is two eletric relays with each having vacumn lines running to them. Anyone know what these are. the Haynes manual does not show the vacumn diagram, typical....

My apologies for the long post, as I stated before, any help or advice would be appreciated

 

Did you use defrost a lot? If so. your heater core/evaporator may be freezing the condensate which would kill your airflow.

Suggestion: put year/model in your post so folks don't have to look at your profile to find it.

Welcome to FTE!

Steve

 

Thank you for the reply Steve. My apologies on the missing information, it is a F150 2001 XLT 4/4 5.4

Never used the defrost excessively, mostly use it as defrost with floor or defrost with panel. Was thinking it may have froze up although when I put a jacket , stuff it under the dash on the glove box side it starts to increase the volumne of air. I see no way for this to make this happen, other than the gasket for the blower motor not being put in. It is a very flimsy gasket and I never seen an original one when I removed the old blower motor, so I never put it in. Not sure how it can blow great when you run for the first hour then continually decreases the air volume.

I do hear a wsshh wsshh under the glove box side, not quite sure if it is actually coming from the other side of firewall where the two relays are that have electrical and vacumn lines going to them. Just perplexed....

 

If a gasket was the problem, it would happen all the time. Putting a jacket on the passenger floor probably blocks part of the floor vents, forcing more air out of the dash vents. I know this time of year in Canada is not a fun time to be checking for clogged condensate drains, but if that's the problem there's no way for the water to drain so it freezes. Is the humidity high when this happens?

Steve

 

Hello Steve

Once again, thank you for your reply. The temperature was minus 20 and it is usually very dry here in the winter time. Doesnt the air get forced through the heater core and not the refrigeration core when on heat in the winter. When I opened up the plenium, the heater core was on the left and the refrigeration core was on the right. I examined the blend door along with the frame the blend door sits in and it all looked good. When I change from cold to warm, the temperature changes.

As far as stuffing a jacket in under the glove box, it restored the airflow rather quickly, not sure if this could defrost something that fast when your driving down the highway. Thats when my wife stuffed the jacket under the glove box because she stated it was freezing her legs. Soon as she put the jacket under the dash, presto, I had airflow on my side and hers, truck warmed up immediately.

I am thinking that the cheap gasket that came with the blower motor has to be installed. I never installed it as there was no old gasket. Maybe it has the blower sucking into the plenium the wrong way, somehow forcing cold air in. I dont get cold air in the panel or the defrost, but there was definately freezing air on the floor side under glove box, even made the passenger side dash cold with the driver side very warm. It was almost like an open vent from the minus 20 below weather was streaming in behind glove box, alyhough this is impossible, I think.....

 

With the humidity that low, it would eliminate the freeze-up problem with the A/C running during defrost (probably doesn't run anyway with outside temps that low). Installing the gasket couldn't hurt, but it sounds like you've got a blend or air diverter control that has a mind of its own. BTW, it's 74* here right now (sorry....couldn't resist!).

Steve

 

Steve, send some of that warm air up here to Saskatchewan, lol. it is suppose to get down to minus 26 tonight....lol

I am going to try putting the gasket in tomorrow, if it doesnt fix the problem, will have to remove the dash again, ouch. Do you know what the two electrical and vacumn relays are for that are mounted on the firewall inside engine compartment, passenger side. looks like some sort of relays, not sure for what.

Stay warm, lol

 

Well, tested the vacumn and have no leaks hurray, lol. What I have found is that when I adjust the temperature control to coldest, I get full air stream, then when I adjust to warmest, I only get about 1/4 air stream. I had my dash out and the darn blend door looked okay. If the motor is stopping in the wrong place would this allow cold air to be sucked into the passenger side of dash? Thinking it is more likely a seal not working in the plenium, anyone ever replace evaporator or heater core seals?

Still perplexing.......

 

When you had the blower motor out, did you clean the leaves and other trash out of the outer heater case? They do build up in this area. I wouldnt be surprised if this is your problem.

 

I'd suspect you'll find a physical obstruction in front of the heater core since the volume of total airflow decreases as the blend door moves to expose more of the airflow to the heater core and less flow can bypass it.

Look for dirt/dust buildup in the core, leaves or other debris, or even a nest from some critter that decided the space in front of your heater core would be a great place to make a home.

Steve