I need some help. Here are the symptoms which may be related or unrelated:

1) No defrost air out of the right vents. The air does come out fine, and with good force on the left side. This occurs even when fans are on max and sound like they are at full speed.
2) Little fresh air (non heated) comes out of the center vents even when fans are on max and sound like they are at full speed.
3) With air conditioning on, cold air comes out of vents, but not very forceful, even when fans max are on and sound like they are at full speed. At times for a few seconds the force of the air coming out of the vents will pick up close to normal and then back off.

General: The fan sounds loud inside the cabin but just not a lot of air to go with the sound.

I have checked the following:
1)All fans seem to be working including; Rear blower, Condenser, Oil cooler, and Both front blower fans. I did replace the condenser ballast resistor and tested both condenser and Oil cooler fans and both speeds work on each.
2) All the servos that i could see at the rear of the luggage compartment appear to be working. Although I am not sure about the recirculation switch. Also I am not sure what the "Fresh air servo" is.
3) I have checked all the fuses in both the luggage and engine compartments and they are all good.

I have questions about a few things that I have read about but not sure how to check or if they could be part of the problem.
1)The rear blower ballast resistor and the 2)differential flapper valves.

Any and all suggestions are welcome.
Thank you,
Peter

 

I have similar problems, also. I have tested the operation of the servos using the test function in the Scantool (like a Hammer), and they all respond. (however, I recently had to replace the right side heat control servo). Air flow from the right side defrost vent is much less than the left side. My airflow overall, for all vents, does not seem to change for the first 3 fan speed settings although the fan speeds increase by sound. But then I get a sudden rush of air at the high setting. But then the fans might not stay on for very long. I also get minimal air flow out of the left side footwell. The left fan does not appear to be working as well as the right side and makes a noise like something might be stuck in it at the high speed setting. So, that is my theory that something is amiss with the left fan and the system is not balanced. I am curious to learn the air flow paths in the unit - it would seem that each fan supplies air to different sides of the cabin, depending on the outlet - defrost, vents, footwell.

 

I have the same problem with the left side foot well, which i forgot to mention, only because it's not as important as fixing the defrost so I can see and the air conditioning.

 

Darrell
Can the "test function in the Scantool (like a Hammer)," check out the 1)rear blower ballast resistor and the 2) differential flapper valves and the 3) fresh air servo?
Thanks
Peter

 

- The Scantool will test both speeds of the rear blower
- It cannot test the differential flapper valves - but, if you are getting heat, the rear blower must be coming on, and the differential valves must be working (but, caveat... not sure what he response might be if one of the two is not working)
- Fresh air servo is tested open-close in the test cycle. (I hypothesize that a portion of my issues may be that the fresh air is not being properly opened and controled)

There is a thread in this forum that lists the test outputs list for the Scantool. I think it was posted by DFinnegan, but not sure.

good luck

 

Thanks for the input, hopefully someone else has had the same problem and has fixed it so I have a place to start. Thanks again

 

Two quick suggestions... Haven't been in there lately. What about flapper door adjustment (or sealing) and those paper like hoses in the footwells.

Talk among yourselves.

 

where would i find the flapper door adjustments and the paper hoses?

 

Flappers are driven from the servos. Check the threaded adjustment arm length to verify that they're closing/opening fully. To check the sealing would take some disassembly. Sorry, working from memory here, and others may chime in that I'm all wet.

Some more stuff here:

http://www.964uk.com/Documents/964%20Heating.pdf
http://www.porsche964.co.uk/technical/servos.htm
http://p-car.com/diy/acdiag.html

Dig into these sites for more great stuff.

 

Just reviewed all the articles, thank you, I have a few things to check in the morning.

 

Does anyone have access to a technical schematic of the hvac system showing all ducting, servos, valves, etc.

 

More stuff here:

https://rennlist.com/forums/964-foru...vaporator.html

Some pics are missing, but Wachuko did a great job on the how-to, and some of the remaining pics may help with your questions on the layout.

http://www.cannell.co.uk/964_Workshop_Manuals/

(Mods: Please delete if this is a violation of Forum/Copywrite rules.)

and-

http://efinnegan.com/Porsche/Pics/HV...CCU/index.html

Dig deeper into efinnegan's site for a ton of links to great archival how-to's.

 

mike
Thank you, the reading begins
Peter