Air/Heater intermittently blowing

Very similar to a current general discussion post but here we go:

Whenever I use my heat or air, it will blow out the vents very weak. It has not always been like this however, when I first got the truck it was great. I didn't use my A/C at all during the summer and when it got cold again and turned the heat on, nothing blows out except at the base of the windshield/top of the dashboard vents.

Sometimes after accelerating to get up to speed on the highway or around town, it will randomly blow strong for a few seconds.

What should I do to troubleshoot?

Vacuum lines or check valve on the passenger side of the intake manifold.

Search "wild vents"

dapepper9 said:

Vacuum lines or check valve on the passenger side of the intake manifold.

Search "wild vents"

Click to expand...

Yeah well there is a vacuum line that I've always had disconnected. Have to splice it into another line sometime. I also don't have 4x4 or cruise control and assumed it was because of that vacuum line. It literally is just sitting on top the engine.

When I did the swap I never got around to plugging it in.

Fix that vacuum line then and see what persists lol

dapepper9 said:

Fix that vacuum line then and see what persists lol

Click to expand...

Add this to the list of weekend things to do I guess. I'll update when I fix it

dapepper9 said:

Fix that vacuum line then and see what persists lol

Click to expand...

Ok it's been forever, but I finally got around to reconnecting the vacuum line. The air still isn't blowing out the vents, any ideas? I'm going to search the wild vents like you mentioned.

Did your cruise control or 4x4 come back?

After reading through the posts, I think its more a blower motor/resistor problem, not vents. Since our vents are vacuum operated they usually make some noise when switching states. You can test to see if they are working by trying a couple things.

1. Let your truck idle for a minute or so to build vacuum in the vacuum reservoir, with the position selector in the defrost position. Then shutoff the vehicle and remove the key. Wait for everything to stop making noise then turn the selector knob to the left one by one pausing for a second on each selection. You should hear either vacuum hissing, or the doors changing state, it usually sounds like a dull clunk or thud.

2. You should be able to find under the dash one of the vacuum actuators if memory serves. While the truck is running change the selection knob until the actuator changes state. If it doesnt change state, gently try to change it by hand. If you are able to change the state by hand I would look into a vacuum issue. Some of the doors may be spring loaded in order to return to the defrost position in the event of vacuum failure. This is a safety mechanism to ensure that failure of the vacuum system does not prevent you from losing vision due to internal glass fogging.

If all the doors are changing states properly, I would move to the blower motor.

Try what i've described and let us know what you find. If it points towards the blower, i'd be happy to help you track down exactly what is causing the problem.

dudeman2009 said:

After reading through the posts, I think its more a blower motor/resistor problem, not vents.

Click to expand...

Thank you so much for helping me.

My cruise control is back ! I don't have anywhere to test out 4x4 right now, this weekend I will. I walked out to my truck on a flat tire this morning so it'll be a few days until I can get another.

I'm going to try the things you mentioned. The only testing I did was last night - took the truck for a 2 minute drive outside the neighborhood and it still won't blow through the vents.

A few points:
- The A/C works, blows cold, but only through the defroster vents
- All settings just blow through the defroster vents
- I'd get a small blow of air through the main vents ONLY after a hard pull up a hill or accelerating to get onto the highway and then immediately letting off.
- I checked all my vacuum lines, none seem rotted, but I might replace anyway, I'll look into it after I try your steps listed.

dudeman2009 said:

2. You should be able to find under the dash one of the vacuum actuators if memory serves. While the truck is running change the selection knob until the actuator changes state. If it doesnt change state, gently try to change it by hand. If you are able to change the state by hand I would look into a vacuum issue.

Click to expand...

Would there be a way to rig the doors to blow thru the main vents always? I don't really need defrost (it's South-Central Texas)

As for rigging the doors, it's possible, but not really easy. They aren't designed to be operated by anything but vacuum, so finding a way to mechanically operated then might prove tricky.

As for the A/C it will only work on a defrost setting or a tagged A/C setting. I'm not 100% on that as my A/C doesnt work, but its that way on every other vehicle i've owned.

Is the fan blowing properly? That wasn't very clear to me.

If the vents only switched momentarily after closing the throttle, i'd be curious to see what the state of the lines are. That does sound like a leak problem, check your lines from where they split and follow it to the selector switch. You can also pull the selector switch off and check for vacuum while running on the connector on back. If you have a small piece of tubing you can manually bridge vacuum from the supply line to the other lines and see if it operates the doors.

Been running around town all day, tomorrow I'll get to working on the truck again and get back to you