pp000830

I have been helping a friend with his HVAC issues on his 993 and put together the below outline based on Tore's diagram below.
I thought others here may find my outline useful or could improve its accuracy or utility by commenting below.
HVAC Diagram

heated airflow sequence:

1. Fresh air inlet at bottom of the drawing, air drawn from behind main engine cooling fan
2. Through a vacuum controlled valve to the left of the engine fan, not shown on drawing
3. Through a duct on top to the auxiliary rear fan, in the engine compartment to the left of the engine
4. Through the auxiliary rear fan, in the engine compartment to a duct leading down under the engine to the left
5. Duct splits off to left & right heat exchangers, I have not seen this as it is not readily visible do others have a picture of this?
6. Through exhaust system heat exchangers, left & right, underneath the engine
7. Past the passive heat dump flap valves, left & right, rubber flaps in housings under the engine
8. Through a connecting duct to the rocker panels,I have not seen this as it is not readily visible do others have a picture of this?
9. Through rocker panels forward to a flex duct leading to the mixing flaps Left & right
10. Through the mixing flap left & right, servo controlled, Ones in the footwell wells that modulate the heat
11. Past the mixing chamber temperature sensors left & right that signal to the CCU that modulates the mixing flap servos left & right, at this point according to Tore's schematic the left and right systems are merged partially through cross flow in the AC Evaporator chamber
12. *Through the blowers left & right*
13. *Then through the footwell/defrost flaps, servo controlled behind dash*
14. *Out of the dash vents*

(*) indicates merged airflow from both heated airflow & cool airflow tracts.

Cool airflow sequence:

1. Front fresh air intake (on the frunk hood in the center)
2. Through the fresh air flap, servo controlled
3. Through the AC evaporator coil
4. *Through the blowers left & right*
5. *Then through the footwell/defrost flaps, servo controlled behind dash*
6. *Out of the dash vents*

(*) indicates merged airflow from both heated airflow & cool airflow tracts.

Cabin recirculation airflow sequence when cabin recirculation button is pressed on the Climate Control Unit (CCU)

1. Vacuum actuated vent allows airflow from cabin via under dash directly through AC Evaporator chamber
2. Through the AC evaporator coil
3. *Through the blowers left & right*
4. *Then through the footwell/defrost flaps, servo controlled behind dash*
5. *Out of the dash vents*

(*) indicates merged airflow from both heated airflow & cool airflow tracts.

Twilightblue28A

Your subject is particularly of interest to me. I had HVAC problems with my 993 and all of the advice provided by other members lead to dead ends. I don't know why there is little interest to help your friend.
Maybe no one knows the correct answers or doesn't know what to troubleshoot after a certain point.
I'm sure if members knew, you would have received responses.

Twilightblue28A

Your post reminds me of difficulties I experienced, sought advice and although most members tried helping for which I appreciate, a few were critical of my efforts.
In fact, one member repeatedly advised me that my driver's side mixing motor was bad, even though I provided photographs to the contrary that my mixing motor operated correctly using the controls. Seemed like the member failed to read the extent to which I troubleshot all of the components and servo motors.
I even recorded the temperatures from each of my vents.
All of the electrical components were scanned and no faults were found. I traced the paper hoses under the dash and the heater hoses back to the heat exchangers and checked the dump valves.
My problem was downstream of the mixing valves. My post was combined and I was advised to seek an expert.
My feelings are that although many members offered their advice for which I deeply appreciated, members couldn't determine the underlying problem.
The personal attacks were and still are inexcusable.

Twilightblue28A

In fact, it seems like my critics went silent......

Too bad. This issue may have affected others, and as result of my experience, others may be too timid to post. My experience can easily expand to other issues, making others reluctant to post.

ToreB

pp000830, thank you for bringing this up. My diagram needed a bit of updating indeed, I have done this now.
The diagram is made to show the different functions, and does not reflect the actual component locations.
Cheers,
Tore

Blue Ocean

Thanks pp000830 for writing this up and Tore for updating the diagram.
Can either of you diagram where and how the air gets separated from the center dash nozzle to the left and right dash nozzles? If in fact, it does.
With heat on, the air from my left dash nozzle seems to be significantly warmer than my center dash nozzles.

Twilightblue28A

Blue Ocean,

I'm glad that you posted your trouble. I'm having the same problem, except that my heated air is much warmer from the passenger's side compared to the driver's side.

I hope that there is a method to repair the temperature differences that we are experiencing.