hb4

I've been working on my AC recently and realized that my Recirc flap never opened. After some disassembly, I discovered that the Recirc and Comb vacuum lines were plugged with a SS screw just downstream from the solenoids. The vacuum tester showed that the recirc, comb, and defrost actuators would not hold vacuum. I replaced the Recirc and Defrost diaphrams and they are now working so I decided to try and figure out how the flaps are supposed be positioned. Looking at the wiring diagram and the three 'Flap Position Program' tables in the WSM has me somewhat confused, so I decided to see how they actually respond in my car (setting the comb flap issue aside for the time being).

After the test, I found two things that I question:

1. In my test, with AC on, the Recirc flap is always open for all positions of the slider, including OFF, except for Defrost. I prefer this operation, but can't figure out how the WD reflects it. Is this the way this flap is supposed to operate? If so, how the heck does the solenoid get power? The WD shows power from Relay IV, through the OFF switch position, and directly to the solenoid, if I'm reading it correctly)

2. When selecting Defrost in all modes (AC, Full Cooling, Full Heat, and No AC/Temp Control) the Recirc Flap opens for about 4 seconds, and then closes. The Control Switch Program on WSM page 87-106 says that the Recirc Flap is closed in Defrost, but the one on page 87-107 says that it is open. So my car seems to be trying to satisfy both pages! Seems to me that the Recirc flap should be open to wring moisture out of the cabin air.

Comments?

WallyP

Per P-80 "Heating Ventilation and Air Condition System" (printed 12/1985)

The flap should be open when the condition lever is all the way to the left, which is the OFF position for the HVAC system.
The flap should be closed when the condition lever is in any other position, EXCEPT when the temp lever is at the left end of the slot, or full cold, when it will be open.

Basically, you get recirculated inside air (flap open) only when the HVAC system is on and on full cold. The flap will be open when the system is off, but the blower is also off, so there is no circulation/recirculation.


Then we go to Pages 87-106 - 87-109 (printed 1986) in the workshop manuals, which give the flap programming.

Page 87-106 says, as you found, that the flap is closed (outside air) on DEFROST.
Page 87-107 says, as you found, that the flap is open (recirculated air) on DEFROST.
Page 87-109 says that the flap is open (recirculated air) on DEFROST.

On my '90 GT, the recirculate flap is closed (outside air) on DEFROST.

hb4

Thanks, Wally

Where is the "Heating Ventilation and Air Condition System" document found?

It sounds like my recirc flap is working correctly in the AC and OFF mode, although I can't see from the wiring diagram how the recirc solenoid is energized in the AC mode. I'll have to study it a little more. Clues from the WD savants will be greatly appreciated.

In the Defrost mode, my recirc flap is as confused as the WSM. It opens for four seconds after reading p.87-107 an 87-109 and then remembers p.87-106 and closes.

I guess I'm happy enough using outside air for the defrost cycle if it works. It's probably drier than the cabin air at that point.

WallyP

Interesting - I have spent many hours going over the HVAC wiring diagrams, and had never realized that the setting motor doesn't appear in the wiring diagrams.

Alan

Setting motor is essentially burried inside the "Control Unit" - odd that they didn't break out more detail there...

The control of the recirculation flap does vary with year, late models (> '90) have the Recirc position (Vs. no off) and this ensures recirculate stays on under all other conditions - however it has a fixed flap position (defrost & vents) so it provides cooler but lower vent airflow - probably a net reduction of perceived cooling on a hot day...

For your year the recirc solenoid valve is controlled by:

A: The off slider posistion (Recirc during off)
and
B: The control unit (setting motor) via the AC relay (Recirc in AC with low temp setting)

Most of the diodes in the circuit have no functional implication - so ignore (spike protection for the solenoid drivers). However there is one diode that has the function to ensure that the water valve is always closed when the recirculate mode is active.

Alan

hb4

Thanks, Alan;
With the confidence that it really was supposed to work the way mine did, I was finally able to figure out this part of the WD. That little horizontal line from the AC relay to the OFF switch threw me.

BTW, when do you think you'll have the 928 electrics download available?

Kevin in Atlanta

Interesting thread...

So, I have a 1991 and the recirc flap does not close for inside air. I have tested with temp slider all the way to the right and the lower slider on recirc as well as with AC on and lower slider on full.

I tested its pod as well as those for the footwell and comb (orange and yellow lines) All is well.

The HVAC head was recently rebuilt via Roger.

Before I pull the console to verify the solenoid is working - how can I test that the it is getting the signal to actuate?