Center Vent
06-14-2001, 03:53 PM
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Center Vent
I am having a problem with the center vent on my 82 928. When I have the heat on (85*) it blows plenty of hot air. When I change the setting to cool (65*) ECO or AUTO, the vent will blow fine for about 1 minute. Then a flap will slowly close off the air so that nothing is coming out. When I turn the heat back on, the vent opens up again.
When I turn the system off I don't have any leekage from the side door vents. When I am in ECO they blow warm air even with the temp set to 65. On AUTO it is cooler but not as cold as the center vent.
Any suggestions. My mechanic wants about $300 to diagnose...
When I turn the system off I don't have any leekage from the side door vents. When I am in ECO they blow warm air even with the temp set to 65. On AUTO it is cooler but not as cold as the center vent.
Any suggestions. My mechanic wants about $300 to diagnose...
06-14-2001, 07:04 PM
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You have a vacuum problem, mostly lkely originating with the hot water shutoff valve (HWSOV).
Only cool air should be coming from the center vent, never warm air.
This is a common problem on older 928s. To determine if the HWSOV is the culprit, remove the air box top and the air filter. Then remove the bottom section of the air box - there is an additional bolt located at the top of the intake plenem towards the rear (the thing with the Porsche crest on it) that holds the lower air box assembly against the intake.
The HWSOV is located under the airbox, near the center towards the passenger side of the car against the firewall. It has a small red vacuum tube and a larger hotwater tube leading to the heater core attached to it.
When this valve fails, it does so in the open position, resulting in hot air always blending with the cold air.
The valve is cheap and easy to replace - around $10 at 928 Specialists - more at other places.
While you're at it, check all the vacuum lines to ensure they are not cracked or leaking at the connections. Be sure to check the connections at the brake booster, the vacuum check valve (remove it, noting the way it is installed - you should be able to blow air through it in one direction only) as well as the connections under the driver's side dash that lead to the vacuum reservoir.
Only cool air should be coming from the center vent, never warm air.
This is a common problem on older 928s. To determine if the HWSOV is the culprit, remove the air box top and the air filter. Then remove the bottom section of the air box - there is an additional bolt located at the top of the intake plenem towards the rear (the thing with the Porsche crest on it) that holds the lower air box assembly against the intake.
The HWSOV is located under the airbox, near the center towards the passenger side of the car against the firewall. It has a small red vacuum tube and a larger hotwater tube leading to the heater core attached to it.
When this valve fails, it does so in the open position, resulting in hot air always blending with the cold air.
The valve is cheap and easy to replace - around $10 at 928 Specialists - more at other places.
While you're at it, check all the vacuum lines to ensure they are not cracked or leaking at the connections. Be sure to check the connections at the brake booster, the vacuum check valve (remove it, noting the way it is installed - you should be able to blow air through it in one direction only) as well as the connections under the driver's side dash that lead to the vacuum reservoir.
06-15-2001, 09:10 PM
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Randy,
Thanks for the reply. I bought a Mityvac and did some tests. The check valve is ok. The line going to the fender (vacuum Reservoir?) does not hold a vacuum. It splits into two lines. I did not test these yet. Where do they go? It doesn't look like I have a lot of room to work in.
The line going into the firewall (to HWSOV?) holds a good vac, no movement on the gage for over a minute. However when I turn on the ignition the vacuum disappears. Is that supposed to happen?
I will probably just replace the HWSOV, but I want to know if I should order anything else.
Thanks for the reply. I bought a Mityvac and did some tests. The check valve is ok. The line going to the fender (vacuum Reservoir?) does not hold a vacuum. It splits into two lines. I did not test these yet. Where do they go? It doesn't look like I have a lot of room to work in.
The line going into the firewall (to HWSOV?) holds a good vac, no movement on the gage for over a minute. However when I turn on the ignition the vacuum disappears. Is that supposed to happen?
I will probably just replace the HWSOV, but I want to know if I should order anything else.
06-16-2001, 09:27 AM
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Remove the carpeted panel on the drivers side of the center console. You can now access the vacuum manifold for the HVAC system individual components. Pull each line out of the solenoid block and test for leakage to each actuator.
HTH-
HTH-
06-22-2001, 06:59 PM
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The vacuum lines to the fender go to the crusie control and to the vacuum reservoir (looks like a black plastic egg carton). Both should hold vacuum. To fix them, remove the fender liner behind the left front wheel.
The line going into the firewall feeds the entire HVAC system. It should hold vacuum, but when you turn the ignition on, several vacuum solenoids open to actuators, valves, etc. Pump madley for a few minutes with the MityVac - if you can never get a vacuum, you have at least one leak. Jay's suggestion on testing at the solenoids is the way to go.
The line going into the firewall feeds the entire HVAC system. It should hold vacuum, but when you turn the ignition on, several vacuum solenoids open to actuators, valves, etc. Pump madley for a few minutes with the MityVac - if you can never get a vacuum, you have at least one leak. Jay's suggestion on testing at the solenoids is the way to go.
06-24-2001, 06:17 PM
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Thanks All,
I repaced HWSOV and I am now nice and cool.
New questions...
1.When I removed the bottom air filter housing, There are two bolts that hold down the housing, and four bolts that hold on the air funnel. On the engine side of the housing these four bolts screw into a manifold that sits freely in a round hole on top of the engine. Is this correct? Only the air filter housing holds this in place?
2.The fan makes some noise after running for a while. I had it on high for a long time with no problems then set it to the middle speeds and got a noise like the blades are hitting/rubbing something. Then back up to high and the noise is still there. No noise on low. Stop the car and rest a while. No noise on high but its there in the middle speeds. After no AC for a while I can live with it. But anyone know of a simple fix? Is replacement hard?
Thanks again
-Jim
82 928
pazificblaumetalic
I repaced HWSOV and I am now nice and cool.
New questions...
1.When I removed the bottom air filter housing, There are two bolts that hold down the housing, and four bolts that hold on the air funnel. On the engine side of the housing these four bolts screw into a manifold that sits freely in a round hole on top of the engine. Is this correct? Only the air filter housing holds this in place?
2.The fan makes some noise after running for a while. I had it on high for a long time with no problems then set it to the middle speeds and got a noise like the blades are hitting/rubbing something. Then back up to high and the noise is still there. No noise on low. Stop the car and rest a while. No noise on high but its there in the middle speeds. After no AC for a while I can live with it. But anyone know of a simple fix? Is replacement hard?
Thanks again
-Jim
82 928
pazificblaumetalic
