hvac vacuum question

[maroman88]

98 s10 blazer, the vents are blowing air where ever they please... it didnt seem like there was enough vacuum to hold the acuators all the way open for the defrost function... i bought a vacuum test kit thing and hooked up the main vacuum line off the engine, didnt hold for ****! so i pulled off the 4x4 line, held perfect! pulled off the emmisions line, held prefect! pulled off the hvac line, didnt hold AT ALL! moved iside the cab, found the main hvac line at the firewall, tested it there, and didnt hold AT ALL... now im assuming it should hold vacuum even when the cars off and hooked up to the tester correct?

[deadtrend1]

yes, it should hold after its off. thats what that little vacuum accumulator ball is for. So when you say floor it up a hill with the heat on, they air will still come out your vents.

[maroman88]

ok so then its gotta be the lines that run from the back of the control unit to the actuators

[greenformula92]

most likely, or the control unit itself isn't getting enough vacuum.