fan only blowing through defrost

Old 07-02-06, 06:44 PM
Thread Starter
Join Date: Jul 2006
Posts: 1
Received 0 Votes on 0 Posts
fan only blowing through defrost

I have a 98 chevy astro that is having issues with the blower for the fan. It only blows through the defrost on both heat and a/c. The switch does allow me to turn high and low speeds. Both heat and a/c work but blow only through the defrost. When I first noticed the problem the air would cut out sometimes (when it was blowing through the vents) and seemed to differ in strength with rpm changes. I get no air through my vents at this time. There are no lights on and I have tried to look to see if there are any lines disconnected but not sure if I am looking in the right place. Does this sound like a vacuum line? If so, how do I find it?
Old 07-02-06, 09:02 PM
Join Date: Feb 2005
Location: Michigan
Posts: 335
Received 0 Votes on 0 Posts
yeah, it sounds like it could be a vaccuum leak. Not sure on your particular vehicle. Look at your intake manifold, there should be some hoses coming out of it. check the condition of them, look for any cracks, splits, etc. theres a lot of them such as one to your brake booster, one to your crankcase, maybe one to an evap canister.

While in park, rev up the engine, hold it at a high rpm, Does it try switching over then?
Old 07-03-06, 09:11 AM
davzack's Avatar
Join Date: Jun 2006
Posts: 304
Received 0 Votes on 0 Posts
Definitely a vacuum leak...classic symptoms and that's exactly what operates the blend door. I've found the best way to search for a vacuum leak is to use starting fluid. Start spraying it under the hood...just a little shot at a time. When you spray near a vacuum leak the fluid will get sucked into the engine and cause it to rev up slightly (Helps to make sure the AC is off when you do this test so as not to confuse engine idle fluctuations for vacuum leaks.) Once you find the leak...replace the hose and you should be okay. Seems like the last two Astro Vans I had this problem with was a vacuum line that was under the hood on the right side (passenger) near the front.
Old 09-05-06, 08:54 PM
Join Date: Sep 2006
Posts: 23
Received 0 Votes on 0 Posts
broke vac supply line to control unit in dash or from contol unit to fresh air vac pod

Thread Tools
Search this Thread
Ask a Question
Question Title: