Ventilation: Blows thru dash vents only; turning vent control knob to floor, defrost or any other setting does nothing. Is this system air pressure/vacuum or electronic and how do I repair?

Asked by Jul 22, 2007 at 11:47 AM about the 2000 Chevrolet Blazer 2 Door LS 4WD

Question type: Maintenance & Repair

11 Answers


Chances are you have a single blower motor under your dash to handle your ventilation needs. Redirecting the air from defrost to vents to floor can be either mechanical (levers and arms) or electronic (computer controlled). If its mechanical then something is either stuck or broken behind your dash causing the air to flow to certain areas and not to others. If its electonic then you may have a blown fuse or relay or blocked valve. Check your fuses and/or relays. Otherwise, take it into your mechanic and have him troubleshoot the problem under the dash.

19 out of 19 people think this is helpful.

If it is like the 2002 Blazer it is vacum controled. A small hard black hose on the Driver's side under the hood goes thru the fire wall and to the AC switch/ vent control on the dash and then to a control box on the driver's side under the dash. There are two hoses going to it (red and green) Check your vacum and then to get at the switch, take off the lower and upper plastic covers. Good luck.

24 out of 24 people think this is helpful.

i had recently had the same issue. anoother cause is the hvac(heat, ventilation, Air conditioning) module is bad. basically all i did was go to a junk yard and got another control unit and hooked it up. the whole control unit in the dash was easily replaced and in under half an hour. it is a common issue in the 01 and 02 models for it to stop working properly.

16 out of 16 people think this is helpful.

Mine was all working great until I put it in the shop to have the head gaskets changed. It came back with this problem, so it seemed like something was reconnected wrong or something. Thanks for the help!

6 out of 6 people think this is helpful.

my chevy s10 2.2 blows air cold or hot through defrost or the lower bottom.. will not blow through the middle vents. regards, RICHARD

39 out of 39 people think this is helpful.

I had a similar problem. There was a broken door inside the vent system, which would not open and air could not get to the floor vents.

15 out of 15 people think this is helpful.

I changed my spark plugs yesterday now the Ac and Heater is blowing out threw the bottom and top not directly at me can anyone help me

27 out of 27 people think this is helpful.

To Anibel: someonE likely busted the vacuum service line to the controls I bet. Getting to sparkplugs can be contortional, and there are quite a few vacuum lines in the same neighborhood.

1 out of 1 people think this is helpful.

I have a problem with my 02 Oldsmobile alero that don't trow air trow the main vents kan u guys help me out plz thanks

4 out of 4 people think this is helpful.

Vaccum controlled HVAC, once in awhile the doors will break, not that often. What needs to be checked... 1- Remove the HVAC module from the dash. --- listen for.hissing comming front from rubber connector -- if hissing, disassemble connector. -- clean rubber air guide disk -- stretch spring out a bit -- with a fine needle clean out vacuum hose ports at connector -- apply small amount of lubricant. ********Make sure to wipe all excess off******** -- reassemble HVAC unit -- leave connector disconnected from HVAC unit -- disconnect hoses -- Remove actuators -- with all hoses disconnected, blow through with pressurized air until you see the actuator end flopping around. -- spray small amount of lubricant inside Actuator ports, door driver bar at the rubber boot, and work the actuator for a minute or two (you will feel it loosen up) -- spray levers and springs on HVAC box and work for a minute or two -- ready male -- issue unsolved? -- check for actuator stuck open or closed. Ive had a couple that tended to stick after they have been treated. Just work it a bit and problem is solved.

1 out of 1 people think this is helpful.

I have a 96 Chevrolet Blazer and I cannot turn off my heat I replace the switch but the heat is still on so can you tell me the problem with it

6 out of 6 people think this is helpful.

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