I'm looking at the WSM, and it makes no sense to me. Under "Flap Position Program," there is a table indicating the recirc flap is closed (fresh air) for all selections of the selector switch (not sure what to call it, but the one that routes air) with the air temp set at max cooling. Then right below it there is another table that says it's open when set to Defrost.

For the center "bulkhead" flap, it says it's open for everything but Defrost (first table) and this matches the second table, but I think this is the "comb flap" thing right? I still don't understand what this does...in another thread, someone made the statement that if this isn't working right, you'll never get max cooling...but this isn't the temperature mixing flaps...that's something else....I think??

Finally, just to further confuse me, the second table says the heating valve is "open" for Defrost and any time you're in the coolest 20% of the temperature selector. Eh? "Open," to me, would mean it's allowing coolant to flow, but they must mean it backwards I guess...

Can anyone translate this for me?

 

I mis-typed that title, but I guess it further goes to illustrate my confusion, so...

 

My take is the first table shows the logic for the flaps without the effect of the blower switch position, AC on or off, and temperature setting motor position. The second table shows the logic of the impact of these items on the logic for the flaps. For example, if the only thing working is the vacuum to the flap actuators then per the first table when the temp lever is at max cooling the Recirc flap is CLOSED to ensure 100% fresh air. If the AC and auto temperature control loop is working then per the second table the defrost position will cause the AC to turn on to dehumidify the air and prevent fogging of the windshield while simultaneously closing the Recirculation flap to recycle cabin air through the heater instead of heating fresh air (faster warming of the air stream), overriding the temp control setting to drive the temp mixing flap(B) to full hot (defrost quicker), opening the coolant (heater) valve to the heater core, closing the "comb" flap(E) to direct more air through the defroster vent (and keep a blast of hot air out of your face) and turning the blower on full speed. The logic of the system is pretty well thought out (maybe over-thought) to provide redundancy in case of single or multiple failures of the automatic control system.

From the Service Supplement to the WSM about the Climate Control system regarding the system from 1984 onwards "The center nozzle is used for ventilation of the passenger compartment. The air volume can be regulated infinitely with a lever on the side of the nozzle. The nozzle can also be closed with this lever, if the draft is found to be annoying. The air shutoff valve of the center nozzle can now be regulated manually with the side control switch, with which the air flow volume can be regulated. A microswitch connected with the shutoff valve control switch opens or closes the center nozzle mixing flap. This mixing flap, when closed, has the task of mixing cold or fresh air with heated air again in front of the center nozzle outlet, to avoid great differences in air temperature.
Control switch in bottom position = shutoff valve closed and center nozzle mixing flap open. Control switch in top position = shutoff valve open and center nozzle mixing flap closed."

I generally put the center nozzle level just closed enough to trigger the microswitch once the cabin is at temperature. This cuts down on the wind in your face but allows enough flow of the slightly cooler air ("has the task of mixing cold [AC] or fresh air again in front of the center nozzle outlet") to have a gentle flow of slightly cool (when the heat is on) or slightly warm (when the AC is on so as not to frostbite your nose) air at your face. This is really nice in the winter when I want my feet toasty but the hot air to the face can make my wife a little over-warm.
Mike

 

But the comb flap is not really the thing that mixes in hot air is it? It apparently has some function, in this area, but given that the temp mixing flap (hidden behind the heat exchanger I think?) is what regulates how much air goes through the heat exchanger, I still don't see how the comb flap has anything to do with the air mix.

Leaving the comb flap for the moment, I THINK I can mostly reconcile the two tables if I think of the first one as vent (AC Off) and the second one as AC On. It's still awkwardly displayed, but that seems to mostly make sense...except for the heater valve row in the second table. That just has to be wrong.

 

The flap description in the WSM are not quite right in my opinion, they tried to combine too much into single diagrams and clarity suffers. I'm not convinced they didn't make a few mistakes also - to me the flap position table for max cooling on page 87-106 is inverted for flap A recirc. The evolution of the controls for HVAC was quite significant over model years and this makes the WSM content relevancy hard to determine.

The recirc flap is in recirculate mode whenever:

- AC is on and temp mixing flaps are in the 0-10% range (this is dependant on temp slider setting AND cabin temp)
- Recirculate is selected (only some models)
- DEFogger mode is selected
- Max AC mode (full left on temp slider)

The comb flap purpose is to allow air from the evaporator to bypass the heater core and be presented directly to the center console & door vents. This creates cooler air faster (particularly if the heater core is hot - which it will be if heating was on before, or if you had parked a warmed up car). This has limited benefits for temperature of air to any other ports - unless the center vent is closed - in which case this cooler air goes primarily to the defroster vents.

Note that not all models have comb flaps, some have airflow flaps in ~the same place that control airflow for the vent (even 2 level airflow flaps) - these are not comb flaps (models 1980/1983). They regulate flow only - not routing.

The comb flap is triggered to bypass the heater core when the temp mixing flaps are in the 0-20% range - this is dependant on temp setting AND cabin temp - Which is why the comb flap can cycle as you drive.

Alan

 

OK, that does make more sense. Thanks!