A/C issue?

1998 CHEVROLET LUMINA
167,000 MILES • 3.1L • 6 CYL • 2WD • AUTOMATIC
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DERRICK WEST
  • MEMBER
  • 1 POST
My Air conditioner when engaged will blow through the vents then stop and start blowing through the floor vents then stop and blow through the vents off and on. Was told it may be the solenoid. Then someone else said it may be the vacuum pump. Grasping at straws!!!
Jun 17, 2023 at 2:27 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,236 POSTS
Hi,

The mode door actuator is controlled by engine vacuum. Under the dash on the passenger side, you will see an electric vacuum solenoid and vacuum hoses will run to different actuators. (See pic below)

I have a question. I need you to pay attention to when this happens. Does it happen when you are going up a hill or when the engine is under a heavy load?

Let me know. Also, take a look under the dash to see if any hoses are leaking, disconnected, or damaged. Also, with the engine running, you may hear a hissing sound if there is a leak. See if you hear anything.

Let me know.

Joe

See pic below.
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Jun 17, 2023 at 3:42 PM
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EASYMONEY79
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  • 1 POST
Having same exact problem, what was determined to be the culprit
Aug 14, 2026 at 4:26 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,236 POSTS
Hi:

The person never replied with a resolution. However, I can tell you that it is related to the mode door actuator.

The mode door is what controls the airflow direction. If it is changing, I suspect you have the same issue as I described. If you pay attention, see if the airflow is more likely to change when the engine is under a load. If it does, follow my aforementioned directions and let me know if you find a leak.

Let me know.

Joe
Aug 15, 2026 at 9:40 PM
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