MAPLT4

I have a '96 LT4 and I have a weird question that I hope someone can help me with. When I turn on a/c or heat, the air blows from the defrost and down below no matter what button is pressed. After driving consistently for about 15-30 minutes the air gradually moves to the center vents. If I press a button at that point it goes right back. I was told that if the green light above the vent buttons was flashing there is an error code similar to the ecu. The light is not flashing. I also heard that the vent system is electronically controlled with vacuum.

If nothing else, it would be better if I could make the air blow through the center vents for the summer, a/c works great. How do I fix this?

Please help!

Marco.

Louis Bartay

My 96 LT4 does the same thing as does a Lot of 96 C4. The vacuum controler that is under the dash by the clutch pedal is losing vacuum. A lot of the time the vacuum line feeding the controler is pinching the now soft rubber male nipple on the controler. You can buy smaller hard vacuum lines that will fit inside the vacuum line so it will not pinch shut.

If you are lucky it is the plastic check valve that is under the fuel rail cover on the passenger side of the engine. Does your cruise control work? If not replace that black plastic check valve and look at the vacuum lines that plug into the intake.

I have not pulled my controler out yet as it is a pain to get to. Usually it is best to remove the drivers seat(if you are a big or tall person) so you can lay on your back to get to the controler.
Good Luck Hope this helps.
Louis

franks96ce

i just finished mine today same problem, i replaced the piece located under the fuel rail cover, and cut the rubber part of the nipples 1/2 way off until it was hard plastic with a razor connected it back and all works well, easy job just time consuming make sure you take off the driver seat.hvac box is black with a blue connection on top and is about 4'' by 4'' against the firewall.

Aggravated4life

Yeah this is a common problem on alot of GM cars...99% of the time,its the plastic check valve on the vacuum line on the engine somewhere.
Even the L98s havt this problem and the check valve is on back of the engine hooked up to the plastic vacuum tubes.

Other engines,theyre under the cover or on top of the engine somewhere.

THat and the other fixes for the Later C4 cars,such as the LT1 or Lt4,cant go wrong with following that info.

larryfs

on the 96, you need to replace the nipples on the box (above the gas pedal). The proper nipples are hard plastic, not soft rubber found in the 96.

I have the correct parts.
pm me if needed.

Louis Bartay

Were you able to make the repair with out removing the box from the fire wall? I read it was a hassle to reconnect the box back on the fire wall. Any other advise would be a great help.
Thanks
Louis

Louis Bartay

Thanks, PM sent with my email address. And any other advise would be a help. I replaced the plastic valve and the vacuum lines under the fuel rail but my AC still blows out the heater ducts.
Louis

Louis Bartay

Larry
Do you still have the parts with hard rubber nipples? I sent you a PM too.
Thanks
Louis