Dear friends:

I am hoping to confirm what I believe are truths about the strange and terrible comb flap for an 86.5.

My beliefs:

1. The comb flap is held open by a vacuum operated diaphragm when vac is applied and held shut by spring pressure in the default closed position.
2. The comb flap should be open with AC on, temp slider to full cold and the vent selector set to the ambiguous rectangle position.
3. The comb flap should close when other settings require diversion of air to places other than the center vent, including closing the center vent and closing the microswitch therein.
4. Jamming the comb flap open will do no harm other than compressing the spring inside the actuator pot and potentially compromising its abilities in the future.

Why do I ask? There is no behavior of my 928's AC system that goes unnoticed by my life companion. One of her many observations is that while the AC system strives to create and maintain meat locker temperatures there are brief intervals where traces of unwelcome warm air emerge from the lower portion of the center vent. I choose at this point not to contest this assertion but note that the intervals are far too brief to be the result of proper freeze switch operation (it has been tested and works to spec). I am therefore obliged to examine other possibilities, including the mysterious comb flap. heat from a heater core that has only the "in" side blocked by a closed manual valve and crumbling foam inside the HVAC box that will have to wait for my dash to come out.

If it is true that jamming the comb flap open causes no real harm, that will be step one. Step two will either be a second valve sealing off the heater core or a bypass valve setup (if it will fit).

Thoughts, random insults and all input will be welcomed.

Thanks

 

Sounds about right to me. As I recall the comb flap is there to help bias flow to the windscreen when demisting is required. In my climate no such need so when my comb flap actuator went ***** up we jammed it open.

Demisting and a/c operation are mutually exclusive I would think.

 

Otto, even with the flap held in place manually there will still be a bit of hot air rising from the heater core.
You have to block the heat (I used a thin piece of black plastic like the ones you find in a binder/folder),
cut to shape and placed over the opening before wedging a piece of wood trim to secure both in place.

Ice cold air all of the time. Refer to Rob Edwards's photos below




Even with center flap held open there is hot air from the heater core exposed



Also refer to this Post
https://rennlist.com/forums/928-foru...-question.html

 

The temperature flaps between the heater core and evaporator close off the heater core. If the temperature control loop is operating or if the temp slider is at full cold.

Bleed from the comb flap is due to deterioration of the sealing foam on the various bits in the HVAC box.

 

Take out the glove box and there is an adjuster that you can reach without too much trouble that on mine had enough left to compensate for the foam loss. Not a big deal.

 

^^what 928NOOBIE says. Adjust those using the WSM procedure to aid in sealing the doors to the heater core.

Or you can bite the bullet, pull the box, and rebuild it with new foam and diaphragms like I did in my 81 and 85. It's annoying but not hard. Worst part is pulling the gauges and removing the old adhesive from the blend doors.

Personally took me about 18 hours but YMMV. Either way you need to make sure all the diaphragms and vacuum system have proper vacuum at all times.

Also, if you have the temp set at anything other than the 2 extremes the car will open and close those blend doors to get the desired temp set as detected by both temp sensors. So you will have random instances of warm air and cold air coming through the center vent.

 

After five children, my mother confided to my sisters "Never trust a diaphragm."

I went through the actuators about 3 years ago and replaced blown ones with Roger's help.

Thanks all for the tips, it looks like there are a number of worthwhile approaches and the one certain thing is that my dash is not coming out this summer, so having alternatives is great.

 

All I can say is with my mod (cover exposed heater and comb flap manually held open) I get 100% cold air, all of the time in Fl. Been 90-100 degrees last 3 weeks and I have no complains.

It was not my original idea, it came from someone else here on RL

 

I had to replace the comb flap actuator recently which restored good aircon, but the air from lower vent is warmer than upper and I’ve never restored the heater box.

I never knew about the adjuster to compensate for foam loss so will consult WSM to see if that still applies to my MY91. In meantime would be very interested to hear more about this procedure and experiences - first time I’ve heard it mentioned!

 

Because there isn’t such a thing even if it can be used for that purpose. And it’s the same across all model years.