HVAC Recirc Control Circuit? Gone Haywire

[Ol'Jim]

Anyone got a control circuit diagram for the fresh/outside air/recirculate system? Mine suddenly began cycling from fresh to recirc & back, every few seconds. I wish it had a full manual control. I generally prefer outside air, unless I am following someone on a dusty road. I know it has dash buttons, and it also overrides your preference in some conditions, (somewhat annoying, but usually only does this on really hot days with A/C running, it will switch to recirc on it's own to try and cool better).
But it has never done this in the heat or vent setting before. Now it keeps cycling several times per minute, no matter what settings or mode I have it in.
Thinking a possible short along the circuit that controls the door/gate for fresh air/recirculate. Anyone ever seen this prob before? Or have any info that might help troubleshoot it? I don't know if the door is vacuum operated, if so it could be a vac line issue?
Thanks in advance for any help you can offer.
-Jim.

[j cAT]

you have no vacuum lines or controls. this is all computer electrical step motors open/closing of the doors for temp and air flow direction.

with the manual or fully automatic HVAC , disconnect the battery negative terminal for a few minutes. with the battery disconnected place the ignition to on to drain any stored volts/power this will hopefully reset things and the AC will again work correctly.

manual control is you control fan speeds and temp with no regulation , which is a knob and variable.

auto control is you set the specific temp ,then the auto ac takes over to keep it at that temp. with this type the computer controlling this is problematic.

[Ol'Jim]

I wanted to post an update to this thread. The original "fix" was to replace the cabin air filter. I bought the truck used, and didn't know it had one, until that problem came up a few years ago. It has a pair of filters in there, and they were dirty. Replaced them, and it was fine. Changed 'em yearly after that. Well, it recently started a very similar problem. About every 30 seconds, I could hear the "recirculate" air inlet open up, then close after about 5 seconds. (Any vehicle always gets a louder noise in recirc mode, as you hear it sucking in air from down under the glove box). So I changed the cabin filters again, (not too dirty), and it is still doing this. Normal for 30 sec, recirc for 5 sec, back to normal for 30 sec, repeating consistently. I switched it from floor/heat mode to dash vent/AC mode, hit the recirc button, to manually put it in recirculate. After a minute, I went back to normal floor vent/heat, and it is again doing the cycling of the air inlet. Any ideas would be appreciated. Or some guidance as to where that gate is located, and is there any way to lock it in fresh air mode? Thanks.