frankvan

Did some digging around the HVAC system today as the defrost is not working properly. When the defrost slider is set to the right or the defrost button is pressed I get air out the drivers side but not the passenger side defrost vents. The servo controlling the defrost flap (on the right hand side (passenger) of the "servo compartment") turns left and right appropriately as do all the servos actually.
My query, is there another flap(s) for the defrost inside the system and are they accessible from the passenger compartment?
Oh, and both blower fans work as I get air out the dash vents and footwell vents when they are selected.

Thanks

Frank

89 C4

canddmf

I just finished reworking my servos and this is what I learned. There are 5 servos under the windshield and function as follows:

When viewed from the front of the car, #1 is far left, #5 is far right

#1, #5 - Direct airflow to windshield (5) and foot wells (1) when sliders are fully right on the CCU.

#2, #4 - Allow in Hot or Cold Air to the manifolds on the passenger or driver sides (respectively).

#3 - Allows fresh air in to the manifolds.

Based on my troubleshooting them, the #1 and #5 servos only bring all air to the windshield or footwells and cannot necessarily fail on the left or the right only. The #2 and #4 servos can fail seperately leading to different air to the driver and passenger sides.

I saw no other controls that might lead to your symptoms as described. Perhaps you have some sort of obstruction in the manifolds?

You might further diagnose full function of the servos with someone's help. Have them adjust the CCU to defrost positions and watch the motions. The CCU takes about 1 - 2 seconds to activate the servos and you can watch them quite easily. I had my son move things as desired till I understood what happened.

From the full cold position with sliders to the left, pressing the defrost button should
- cause servo #1 to rotate
- cause servo #3 to rotate (if in recirculate position, I think - not sure on that).

Turning up the heat should cause both #2 and #4 to rotate to where the actuator is pushed toward the baffles.

Your description sounds more like either foreign matter in the ducts or a disconnected (partially) duct.

Good Luck

Chuck

frankvan

Did some more digging around and found the following:
- fan for A/C in front left fender (in front of wheel) is seized. (oil cooler fan thankfully works just fine in the right front fender)
- all 5 servos respond correctly to commands from CCU
- rear (engine) blower comes on when CCU turned above blue dot
- on fan speed 4 and at blue dot for temp air flow is great out of left hand defrost and both footwell vents when sliders are appropriately selected.
- on fan speed 4 and at blue dot air flow is almost non-existent out of dash vents (with sliders to full left and vents opened )
- NOW with all my fiddling, the two front blowers turn off (completely) when the temp **** is above the blue dot, but the rear engine blower kicks up to full speed. Because of the seized AC fan I tried this with and without the AC blower relay connected (R14)
- fuse for rear blower is fine - relay is a different story as demonstrated by attached pictures....I think previous owner had problems with this! Unfortunately my service records only go back to '98 so I am not sure who did this when!

(does anyone have the wiring diagram for the rear blower relay????)

I also checked out these similar posts:
https://rennlist.com/forums/showthre...t=defrost+heat
https://rennlist.com/forums/showthre...t=defrost+heat
https://rennlist.com/forums/showthre...t=defrost+heat

At least the car still drives nice, it's summer, and I can just roll down the windows and open the sunroof

Frank

89 C4