HVAC System Wiring Diagram

[kontinuous]

Hi Gen Vibe group, I am working on my Recirc servo for the second time. This time I am installing a new servo. I have the part, but I am concerned about whether or not I may just end up killing this one as well. So I started to wonder, what is the limit stop on/for this actuator. One poster stated that it is contained in the unit. looking at the guts I don't see how.

So, out to the car for some testing.

1) When I run it free from the redirect flapper (foam covered piece in the duct work that it is moving) it does not stop, it will just keep turning until (for too many of us) it hits a broken tooth.

2) I put a multi-meter on the plug with wires. Positive with switch in re-circ mode, negative when not (depending on lead placement). There does not seem to be a timer on the circuit (i.e. negative or positive for 20 sec then 0 volts) as experienced with test 1 and this multi-meter test.

3) Still with multi-meter attached, I moved the redirect flapper back and forth until it stopped, no voltage change, so it does not seem like there are any limit switches or position sensor in the duct work.

What am I missing here? Is the design to actually keep power this motor/servo constantly, just switching between negative and positive based on the recirc switch? All the time pushing up against the mechanics? If so, no wonder they keep breaking

Does anyone have a schematic of this particular circuit that may indicate limits for this servo?
I have heard of a HVAC system controller, is there such a thing and could it not be limiting voltage to the servo?
Could there be a problem hidden somewhere else in the circuit that is not taking it to zero voltage when in either closed or open position?
Something in the switch?
Resistance (mechanical transformed to electrical) sensor somewhere?
Time for a cable and big lever to manually move that flapper?

[joatmon]

What am I missing here? Is the design to actually keep power this motor/servo constantly, just switching between negative and positive based on the recirc switch? All the time pushing up against the mechanics? If so, no wonder they keep breaking

I do not think you are missing anything. I am pretty sure that the design is to always provide power to the motor, and yeah, no wonder they fail.

I looked at the wiring diagram for the circuit (attached). It doesn't show any sort of limit switch or timer control. It doesn't show the inner workings of the AC / Recirc switch, so if there is any kind of timer, it would have to be in there. I've looked at that switch, and do not think it is anything more than just a simple switch. Not scientific, but the fact that they implemented a mechanical cable to kick out of recirc when in defrost mode to me indicates that the recirc circuit was designed without much electronic complexity

[kontinuous]

Thanks for the diagram joatmon. Based on that and what I see in the car, I have made a modification that I hope will allow the new servo to work longer before failing. It is not pretty at this point, but it proves to work as I expected.

Essentially it is a power on/off OF the recirculate circuit/switch. I use the space of the third button to install a simple on/off switch that I put in line with the Green/White wire heading to the servo. So, if the driver wants to change the air source to the blower, this new switch must be in active state in order for the position of the recirculate button to work (or be active). It takes about seven seconds to switch from recirculate to fresh air or back. If you turn the switch off at some point less than seven seconds, you can get a mix of recirculate/fresh.

The additional switch

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The Module with salvaged wiring harness

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The Green/White wire, cut

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[kontinuous]

Here are the remaining three images of what was done. I may make the switch look better, but at this point I have not destroyed any of the plastic to where I could not restore to the original state.

The male part of the switch harness spliced in

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Harness attached and ready to install face bezel

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Complete, albeit not the best looking yet

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During this process I had to remove the cable connecting to the bottom of the module. This actuated very easily and when I did actuate it, the recirculate flapper did not move. I suspect it is defrost related, but did not locate what the cable actually operated. Maybe another day.

[lannvouivre]

During this process I had to remove the cable connecting to the bottom of the module. This actuated very easily and when I did actuate it, the recirculate flapper did not move. I suspect it is defrost related, but did not locate what the cable actually operated. Maybe another day.

Yes, it's for defog.

[joatmon]

The mechanical cable that connects to that switch assembly is also connected to the air direction control, and extends when the air direction is set to full or half windshield (defrost). When the cable extends, it trips the latch on the recirc switch, putting it back into fresh air mode. Defogging the windshield does work a lot better with fresh air, so I guess they figured it was worth adding such a link. I almost never use recirc, so I tend to leave that cable disconnected.

[kontinuous]

Ahhh, that makes sense. The switch portion I was working on does not actuate the cable, the cable is actuated by the dial which in turn actuates the switch (recirc button) to make sure fresh air is being used.

Interesting for sure as how most things have gone electronic or vacuum, they throw in a cable to add a touch of retro.

Thanks again for your help!