1997 Chevy Blazer Air ducting problems

CNTRYBYWLKR

MEMBER
1997 CHEVROLET BLAZER
6 CYL
4WD
AUTOMATIC
168,000 MILES

I recently purchased a 1997 Chevy S10 Blazer. When you turn the heater or a/c on it will only blow out the defroster portion of the duct work. All duct work is on the vehicle. I have already replace the climate control unit being the easiest and cheapest. I wanted to find out if you possible know what could be causing this? Thank you for your time and support.

Wednesday, June 10th, 2009 AT 10:27 PM

1 Reply

SWILLIAMS

MECHANIC
597 POSTS

Likely cause is a bad vacuum line leading to the dash controls. The common break point is right at the plastic tree connector that is located between the brake booster and drivers side fender. The plastic cracks and you lose vacuum.
Default position in the event of vacuum loss on most heating systems is to switch to defrost mode.
It could also be a defective vacuum reservoir or line going to it. That is the ball mounted under the hood on the drivers side. If the lines on it are cruddy, flaking replace ALL the vacuum lines. Cheaper and easier than doing them one at a time.

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Tuesday, June 16th, 2009 AT 1:32 PM