with your mouth
Start out by checking for a vacuum leak both inside and outside for the a/c and heater.........
You have a vacuum leak somewhere. Trace the main vacuum hose fom the air intake until you find a crack in the hose.
vacuum leak
Check for a vacuum leak either under dash or under the hood Check the operation of the vacuum actuated motors under dash Check the selector switch
P2173 High AirFlow/ Vacuum Leak Detected (Slow Accumulation).You have a vacuum leak in the intake manifold.P2173 High AirFlow/ Vacuum Leak Detected (Slow Accumulation).You have a vacuum leak in the intake manifold.
vacuum leakTo
ussualy you can spay the vacuum lines and intake with wd40. watch where you are spraying and if it revs above an idle you found the leak.
You can find a small vacuum leak in your 2002 Toyota Camry with a diagnostic tester. The diagnostic tester can pinpoint virtually any vacuum leak.
Some systems use engine vacuum to move the control doors. You could have a vacuum leak.
It's a vacuum leak somewhere in the system. There are several vacuum lines that operate the blend doors on the system. If there is a leak where the system will not hold vacuum, it will default to defrost automatically.
To find a vacuum leak. the vacuum hoses should be sprayed while the engine is running. A solution of dish soap and water sprayed on a leaky vacuum hose will cause it to blow soap bubbles. Spraying both the hose and the connectors should find the vacuum leak quickly.
First you have to locate the source of the vacuum leak then you can determine what steps to take to stop the leak. Determine the source and re-post your question with more info.