Ok so I'm new here and have tried searching and haven't really seen what I'm after.
Just got this truck and the ac does blow cold air. However
when I goto max ac. The fan speed stays same as on hi.
Also. When I'm on the road and gas truck too much the airflow stops until I let off gas. I was told it's a vacuum line issue and started fiddling today.
Since its 115 in Arizona now days I have to work on it right before dark.
So. I pulled the controls from dash and when I turn to max ac I can hear a vac leak where the plug goes with all the colored lines on it. I tried pushing it in more etc ad nothing really stops the noise. Fan still stays on hi speed no change.
I ended up unhooking the rod that goes to an actuator almost right under the ashtray to the right a little. So I could flip the flapper to one side and it comes out of the vents now. But I still don't know what the deal is with the airflow.
I did see someone has a line plugged off under hood
it is in a black box thing behind the battery a little. Has a red black and white line to it. The red one was broken so I plugged it in just to check but my truck ran like total crap wouldn't even stay running or start. So I unhooked it?????
no idea what to do here never had vac controlled air before. Btw I think it's a crap idea for the record.

Any help id appreciate greatly since I sweat my **** off here in Arizona.

 

The problem is the "no idea" part, not that it is vacuum controlled, like I figure well over 100 million vehicles have been over the years.

The fan speed should NOT change. Going to "Max" changes the position of the Outside Air/Recirculate door, which is just above the passenger's feet. When in Max, the door closes to outside air, and opens to inside the cabin air for the suction side of the fan. If working properly, the fan should sound noticeably LOUDER in Max, as there is a near-direct sound path from the blower wheel thrashing around, through the now-open recirc door.
Put it in Max, with it running. Is the door closed, or open down there? Easy to bend down and check it.

Vacuum problems are often caused by a well-known degradation of a length of plastic hardline vacuum hose to the vacuum motor that controls the Outside Air/Recirculate door. Under the hood, on the passenger side, by the firewall, on top of the blower case, can see the vac motor and its bellcrank. Look for a white vac hardline, its thin, may be discolored to yellowish or browish white. It comes out of an electrical harness, and connects to the vac motor. If there is a break anywhere, it is a vac leak. If bad, will probably have to unwrap a bit of the harness to get back to solid non-crumbly plastic hose. Can get a length of 1/8" or so inside diameter rubber vac hose to replace the bad section. Force it over the plastic hose.

Have no idea at all what you are in to there with that description!

 

I'll get some pictures under the hood
I think it's the ac vacuum holding box?? It's right in front of where you charge with freon if that helps any. Pretty big actually.

the actutor by passenger left feet will only open all the way if I push on the connector at the control. When I let go of the plug that slowly creeps back and the flow of air either stops or is nil at best.
There is never a sound change. Once I go to hi fan speed that's it. When I goto max ac nothing at all changes. No more flow no louder zip.

Wverything i I ever had had massive air flow when u went to max ac setting. Heck the way it is now it can't even keep cab cool on a hot day.

What about losing airflow when gassing truck to pull a hill or keep up ur speed on highway. Pretty much gassing it more than barely touching pedal. Which seems to be most the time unless going downhill.

 

Even on Max AC, fan high is still fan high, it doesn't go any higher than that. The only difference between AC and Max AC is on Max the recirculation door closes and cabin air is recycled to improve cooling instead of pulling in hot air from outside. People often confuse the noise of air rushing through the recirculating duct as a faster fan speed but it's not.

The HVAC vacuum line from the vacuum reservoir located behind the battery is notorious for breaking and causing the loss of vent control during acceleration or hill climbing.

 

im guessing that is breaks internally? I can pick up another one. I'm getting hose to repair the broken line also.
since it's 109 out I have to wait to work on it.
If that is broken could that explain why the truck wouldn't run when I plugged the red line back in? Or is that another issue?


Thanks for for all the help

 

Due to the relative ease of recirculating cabin air versus the load on the blower of taking in outside air and also exhausting it, the lower static resistance to airflow often does cause a realized increase in the blower's speed.

 

Yes I understand positive cabin pressure...I was speaking electrically, there is nothing higher than high, regardless of regular or Max AC selections.

 

Sure, just clarifying that the motor is not controlled to go faster, it just has that possibility due to reduced resistance to airflow when in MAX A/C.

 

ok I found the white line from wire harness to the actuator under hood by passenger firewall was cracked and brittle. I replaced the line from actuator to harness.
This didn't have any effect. I unhooked the actuator and made sure door flips back and forth. I switched from ac. To max ac and the actuator didn't move.
When at max ac I can hear a leak at the plug on back of the control switch in dash. Another on the way.

I had truck running and hooked the red the red line back up see photos. And truck died almost instantly. Cranked and cranked nothing. Unhooked and plugged off and after some cranking fired up and ran fine.

Does this his mean that the canister that these lines goes into is bad??
i only see one other plugged line on top of engine see pics.

The check wngine light does come on after I drive truck idling it does not. Anywhere from a hundred yards to half a mile depending on how long truck has been shut off.
Idk if that's related to the red line u hooked or what??

chilton book isn't here yet so can't really see what's what but I know something has to be wrong to make truck stall u less that red line from canister is u hooked ya know??
Pics shows what line I mean.