Blend door operation

[6.9poweredscout]

I'm assuming the blend door is connected to that vacuum actuator on the heat/AC box under the hood correct? Now I've never had a issue with heat or AC and the fan blows good on all settings. I did the heater hose vacuum actuator valve to help get cooler AC. Hooked it all up and switched it to max AC with the lever all the way to cool and fan on high and looked at the blend door actuator.... Didn't move. I pulled the vacuum hose off and the actuators changed positions but nothing changed in the vents. Still lots of cold air blowing. Sooooo what does the blend door do? If nothing changed opened or closed what does it mean? It's got full vacuum so I know that half works, setting it to max AC should change something right? Oh and before someone asks what vehicle from not reading my signature, it's a 1991.

 

[franklin2]

The max A/C position just changes the actuator out at the hood hinge on the pass side. That actuator selects a door to pull the air from the wiper/cowl area, or it pulls air from inside the cab. That's what max does, pulls air from the inside. I believe the blend door is controlled by the temp lever.

If you study the article about putting the Ranger water valve in your truck, you will notice you are putting a tee into the line that goes to that actuator over at the pass hood hinge.

 

[chris142]

the blend door is cable operated.the cables are easily acessed from behind the glove box

 

[6.9poweredscout]

Ah. Works fine. Thought the max AC setting moved them. The cold/hot lever works them. Thanks!

 

[LCAM-01XA]

Just a heads-up, keep an eye on that bypass valve, aftermarket ones are not exactly of the greatest quality and in my experience their longevity is questionable especially if your engine runs higher RPMs. That's why I got rid of mine, can't chance being sidelined 1000 miles from home by some cheaply made POS that I installed too. And I never saw a noticeable difference in A/C performance with it in there, so hardly a big loss.

 

[6.9poweredscout]

I pulled it off a ranger in the junk yard.

 

[LCAM-01XA]

Then it probably won't blow apart violently, but will instead seep thru the seal for the butterfly valve shaft. No big deal then, just makes an annoying mess over time. If you ever open the hood and smell coolant, check the valve shaft seal under the vacuum pod. Curious tho, do you notice any improved A/C with the valve in? I couldn't tell the difference, must mean my blend door seals are still pretty good.

 

[6.9poweredscout]

I haven't had to run the ac yet, just getting ready for the heat while its cool out still.

 

[Clb]

fwiw on my 88 it (shutoff valve) made a huge difference on nice days Where the ac was off and windows open.

 

[dgr]

My ranger bypass valve made a measurable difference in A/C temp by way of a digital thermometer. If my compressor didn't decide to blow its shaft seal this winter, I'd give you exact numbers.

LCAM is right about the valves leaking at the shaft. My cherokee uses the same design and randomly leaves a little trail of coolant on the driveway. It appears to only leak when the cooling system is coming up to pressure but hasn't fully warmed yet. It's almost annoying enough to change it out for a new, likely defective, one.

 

[chris142]

sounds like some of you need to adjust your blend door cable so that the door shuts completly or your foam seal is damaged. mine will get downright frigid in the cab with r134a in it and no extra heater valve.

 

[LCAM-01XA]

Chris, yes, both of your points are very valid. Cable is easy enough to fixs, but I'd imagine the foam seal issue would be more prevalent among people living in the north cue to running the heat more often and at higher temperatures and thus cooking the seals to powder. But since you mentioned R134, and this is kinda A/C-related thread, I have a question for you - do you know what orifice tube are you running in your A/C system? Parts stores list multiple fixed and auto-variable tubes for trucks like yours, I was just wondering what work so good for you?

 

[Clb]

Fwiw
Lube the pod and linkage with dry sillycone
Mine would drag open/close before now it runs free

 

[79jasper]

You will still get some heat soak from the heater core, without the valve.
I would think mid/southern trucks would have the seals eaten up. I've recorded about 150°F interior temp on a fairly hot day. (Windows up and sitting til noon) but I guess coolant temps are quite a bit hotter, so never mind my theory.
Chris, just imagine what it would be like it you had a valve installed. ️


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