Alright folks need help
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Launching!
Joined: Oct 2010
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Alright folks need help My a/c heat is only blowing out of the top and bottom vents but not the main vents. I have asked this question before everyone said vacuum lines but nothing is wrong with any of them i have also searched this and found nothing. If anyone could post pics it would help i have a 1 year old that i am taking to daycare now so i really need to have this fixed before it gets really cold. Thanks.
TECH Regular
Joined: Oct 2011
Posts: 407
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From: Keller Tx
Here is SHBOX link to this problem
Restore Airflow to the Dashboard Vents
This is a common fix for when the air no longer blows out the vents. When there is not enough vacuum to operate the actuators, they will only direct air to the floor and defrost ducts by default. Diagram of HVAC system. You may also notice this happening under hard acceleration or going up a long, steep hill (times when engine load is high and vacuum is low). This might mean you have a small leak.
An easy way to tell what part of the system may have trouble is to go to the vacuum check valve and test the lines back to the mode selector, intake manifold and to the vacuum tank. The check valve often cracks and is the source of a leak, so be sure to inspect and/or test it. The line to the vacuum tank can often get a hole just under the battery box. It can rub where it passes through the chassis and/or deteriorate from battery acid contamination.
A hand held vacuum pump (like a Mityvac), makes testing pretty easy (your lungs can be used as an alternate vacuum source ;-) or you can blow through the lines and listen for air escaping). At the check valve, remove the hoses one at a time and apply vacuum to each and see if it holds. The line to the intake manifold will have to be removed at the manifold and plugged back toward the check valve for you to test the line for leaks. If you find a leak on a particular hose, you will have to trace out the cause on that section.
Restore Airflow to the Dashboard Vents
This is a common fix for when the air no longer blows out the vents. When there is not enough vacuum to operate the actuators, they will only direct air to the floor and defrost ducts by default. Diagram of HVAC system. You may also notice this happening under hard acceleration or going up a long, steep hill (times when engine load is high and vacuum is low). This might mean you have a small leak.
An easy way to tell what part of the system may have trouble is to go to the vacuum check valve and test the lines back to the mode selector, intake manifold and to the vacuum tank. The check valve often cracks and is the source of a leak, so be sure to inspect and/or test it. The line to the vacuum tank can often get a hole just under the battery box. It can rub where it passes through the chassis and/or deteriorate from battery acid contamination.
A hand held vacuum pump (like a Mityvac), makes testing pretty easy (your lungs can be used as an alternate vacuum source ;-) or you can blow through the lines and listen for air escaping). At the check valve, remove the hoses one at a time and apply vacuum to each and see if it holds. The line to the intake manifold will have to be removed at the manifold and plugged back toward the check valve for you to test the line for leaks. If you find a leak on a particular hose, you will have to trace out the cause on that section.
