Early HVAC vacuum diagrams & central locking (must read for 78-79 owners)
09-07-2013, 03:55 PM
#1
Rennlist Member
Thread Starter
Early HVAC vacuum diagrams & central locking (must read for 78-79 owners)
Round Two of HVAC vacuum troubleshooting led to hours of reverse engineering to figure out what was Porsche thinking.
What I found was the Porsche diagrams (Service Information booklet, 1978, pgs 130-131) were very inaccurate and lacking info. I'd suggest not using them.
Now I understand why early car owners have struggled to get their HVAC system functioning properly (after what I went thru, I'd say near impossible).
The following information should help you get your system working properly.
This should apply to both MY78 and 79 (however, I wasn't able to test a 79, so YMMV)
To download PDF version CLICK HERE
What I found was the Porsche diagrams (Service Information booklet, 1978, pgs 130-131) were very inaccurate and lacking info. I'd suggest not using them.
Now I understand why early car owners have struggled to get their HVAC system functioning properly (after what I went thru, I'd say near impossible).
The following information should help you get your system working properly.
This should apply to both MY78 and 79 (however, I wasn't able to test a 79, so YMMV)
To download PDF version CLICK HERE
Last edited by Jadz928; 09-07-2013 at 04:50 PM.
03-31-2020, 11:22 PM
#5
Rennlist Member
I have started testing my HVAC system and have some questions related to the information posted above by Jim. First I should mention that the central locking system has been dismantled, the vacuum tubing is in the doors, but not attached to anything in the door. I have not yet tracked down the other end. Also my air conditioning system has been deleted, so what I have left is a heater and ventilation system.
From the vacuum hose termination manifold I have tested most of the lines and can see or hear the various flaps and valves working (including the heater valve), so that part seems to be OK. The problem is between the brake booster vacuum line and the manifold I am only able to get a weak vacuum, which would explain why I don't get any heat.
In the diagram there are two vacuum reservoirs, one on each side of the firewall. On my car there is none on the engine side of the firewall and no indication that there has ever been one. There is a reservoir (three large spheres) under the dash near the driver's door... but the tube that is connected to it has been cut and sealed with a screw. The tubing is hidden between the firewall and where it becomes visible before crossing from the driver's side to under the console so I can't see what is in there... originally there should have been a couple of tees or perhaps a four-way connector.
It doesn't look like there is an easy way to get access to that part of the tube short of removing... the instrument pod? ... the dash?
Can the system work without the reservoir? I could just run a new tube from the brake booster to the manifold to get decent vacuum...
From the vacuum hose termination manifold I have tested most of the lines and can see or hear the various flaps and valves working (including the heater valve), so that part seems to be OK. The problem is between the brake booster vacuum line and the manifold I am only able to get a weak vacuum, which would explain why I don't get any heat.
In the diagram there are two vacuum reservoirs, one on each side of the firewall. On my car there is none on the engine side of the firewall and no indication that there has ever been one. There is a reservoir (three large spheres) under the dash near the driver's door... but the tube that is connected to it has been cut and sealed with a screw. The tubing is hidden between the firewall and where it becomes visible before crossing from the driver's side to under the console so I can't see what is in there... originally there should have been a couple of tees or perhaps a four-way connector.
It doesn't look like there is an easy way to get access to that part of the tube short of removing... the instrument pod? ... the dash?
Can the system work without the reservoir? I could just run a new tube from the brake booster to the manifold to get decent vacuum...
