79 HVAC vacuum check questions
06-14-2014, 12:12 PM
#1
Rennlist Member
Thread Starter
79 HVAC vacuum check questions
Have the dash out and have tested all the HVAC actuators and replaced those that were leaking.
When I disconnect the black vacuum supply line from the HVAC control head and pull a vacuum on the supply side it holds a vacuum.
When I connect to the supply line in the engine bay going into the car I can pull a vacuum and watch the main HVAC door between the blower and the heater/ AC exchangers close but the system will not hold a vacuum.
I would have expected to be able to vacuum down the reservoirs and get them to hold for a while based on the way I understand the system to work.
Do I have a problem or just a lack of knowledge on the system?
When I disconnect the black vacuum supply line from the HVAC control head and pull a vacuum on the supply side it holds a vacuum.
When I connect to the supply line in the engine bay going into the car I can pull a vacuum and watch the main HVAC door between the blower and the heater/ AC exchangers close but the system will not hold a vacuum.
I would have expected to be able to vacuum down the reservoirs and get them to hold for a while based on the way I understand the system to work.
Do I have a problem or just a lack of knowledge on the system?
06-14-2014, 12:23 PM
#2
Nordschleife Master
You're working from the line that attaches to the vacuum source in the engine bay? That should hold vacuum.
If you're including the brake booster and cruise module then those may leak.
If you're including the brake booster and cruise module then those may leak.
06-14-2014, 12:58 PM
#3
Rennlist Member
Thread Starter
I disconnected the black supply line that runs front the T after the check valve off the brake booster and that runs through the fire wall.
I have since went into the car and vacuumed down the black supply line going into the HVAC control head and can pull a vacuum and get the defroster and main valves to close as they should but it will not hold a vacuum at the control head. Perhaps the PO did not have everything connected properly and I have line going to atmosphere that should not or I have problem at the control head with a seal.
I have since went into the car and vacuumed down the black supply line going into the HVAC control head and can pull a vacuum and get the defroster and main valves to close as they should but it will not hold a vacuum at the control head. Perhaps the PO did not have everything connected properly and I have line going to atmosphere that should not or I have problem at the control head with a seal.
06-16-2014, 09:27 AM
#4
Rennlist Member
Thread Starter
Update.
I used the vacuum guide from 928 Classics web site to ensure I had everything where it belongs.
The main, foot well and defrost valves all test good. The recirc valve was bad and NLA so waiting on a late model heater housing and have the recirc valve locked to allow internal air only for the time being. That vacuum line is capped off.
I am still struggling to get vacuum to the main and foot well valves. Main is open with no vacuum so no big deal and the foot well is closed with no vacuum so thats fine also.
Still have the issue of not holding a vacuum with HVAC controller connected when pulling a vacuum on the black supply line. Is my HVAC controller bad?
I used the vacuum guide from 928 Classics web site to ensure I had everything where it belongs.
The main, foot well and defrost valves all test good. The recirc valve was bad and NLA so waiting on a late model heater housing and have the recirc valve locked to allow internal air only for the time being. That vacuum line is capped off.
I am still struggling to get vacuum to the main and foot well valves. Main is open with no vacuum so no big deal and the foot well is closed with no vacuum so thats fine also.
Still have the issue of not holding a vacuum with HVAC controller connected when pulling a vacuum on the black supply line. Is my HVAC controller bad?